Android 异步加载神器Loader全解析

在之前呢,我们经常会有这种需求,比如在某个activity,或者某个fragment里面,我们需要查找某个数据源,并且显示出来,当数据源自己更新的时候,界面也要及时响应。

当然咯,查找数据这个过程可能很短,但是也可能很漫长,为了避免anr,我们都是开启一个子线程去查找,然后通过handler来更新我们的ui界面。但是,考虑到activity和

fragment 复杂的生命周期,上述的方法 使用起来会很不方便,毕竟你要考虑到保存现场 还原现场 等等复杂的工作来保证你的app无懈可击。所以后来呢谷歌就帮我们推出了一个

新的东西---Loader。他可以帮我们完成上述所有功能!实在是很强大。

如果你有阅读英文技术文档的习惯 那么谷歌官方的文档 也许比我所说的更加完美。具体可以参考如下:

http://developer.android.com/intl/zh-cn/reference/android/app/LoaderManager.html

http://developer.android.com/intl/zh-cn/reference/android/content/AsyncTaskLoader.html

http://developer.android.com/intl/zh-cn/guide/components/loaders.html

我所述的内容也是主要基于上述三篇文档。

首先呢,我们来看第一个例子,这个例子也是官方的推荐了,我给简化了一下,主要是监听手机里 联系人这个数据源。当数据源改变的时候 自动update 我们的ui。

  1 package com.example.administrator.modifytestview;
  2 
  3 import android.app.Activity;
  4 import android.app.FragmentManager;
  5 import android.app.ListFragment;
  6 import android.app.LoaderManager;
  7 import android.content.CursorLoader;
  8 import android.content.Loader;
  9 import android.database.Cursor;
 10 import android.net.Uri;
 11 import android.os.Bundle;
 12 import android.provider.ContactsContract.Contacts;
 13 import android.util.Log;
 14 import android.view.View;
 15 import android.widget.ListView;
 16 import android.widget.SimpleCursorAdapter;
 17 
 18 public class MainActivity extends Activity {
 19 
 20 
 21     @Override
 22     protected void onCreate(Bundle savedInstanceState) {
 23         super.onCreate(savedInstanceState);
 24         setContentView(R.layout.activity_main);
 25         FragmentManager fm = getFragmentManager();
 26         CursorLoaderListFragment list = new CursorLoaderListFragment();
 27         fm.beginTransaction().replace(R.id.root, list).commit();
 28 
 29     }
 30 
 31 
 32 
 33     public static class CursorLoaderListFragment extends ListFragment
 34             implements LoaderManager.LoaderCallbacks<Cursor> {
 35 
 36         // This is the Adapter being used to display the list's data.
 37         SimpleCursorAdapter mAdapter;
 38 
 39         // If non-null, this is the current filter the user has provided.
 40         String mCurFilter;
 41 
 42         @Override
 43         public void onActivityCreated(Bundle savedInstanceState) {
 44 
 45 
 46             mAdapter = new SimpleCursorAdapter(getActivity(),
 47                     android.R.layout.simple_list_item_2, null,
 48                     new String[]{Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS},
 49                     new int[]{android.R.id.text1, android.R.id.text2}, 0);
 50             setListAdapter(mAdapter);
 51 
 52             //这个地方初始化了我们的loader
 53             getLoaderManager().initLoader(0, null, this);
 54 
 55             super.onActivityCreated(savedInstanceState);
 56         }
 57 
 58 
 59         @Override
 60         public void onListItemClick(ListView l, View v, int position, long id) {
 61             // Insert desired behavior here.
 62             Log.i("FragmentComplexList", "Item clicked: " + id);
 63         }
 64 
 65         // These are the Contacts rows that we will retrieve.
 66         static final String[] CONTACTS_SUMMARY_PROJECTION = new String[]{
 67                 Contacts._ID,
 68                 Contacts.DISPLAY_NAME,
 69                 Contacts.CONTACT_STATUS,
 70                 Contacts.CONTACT_PRESENCE,
 71                 Contacts.PHOTO_ID,
 72                 Contacts.LOOKUP_KEY,
 73         };
 74 
 75         //只会调用一次
 76         public Loader<Cursor> onCreateLoader(int id, Bundle args) {
 77             // This is called when a new Loader needs to be created.  This
 78             // sample only has one Loader, so we don't care about the ID.
 79             // First, pick the base URI to use depending on whether we are
 80             // currently filtering.
 81             Uri baseUri;
 82             if (mCurFilter != null) {
 83                 baseUri = Uri.withAppendedPath(Contacts.CONTENT_FILTER_URI,
 84                         Uri.encode(mCurFilter));
 85             } else {
 86                 baseUri = Contacts.CONTENT_URI;
 87             }
 88 
 89             // Now create and return a CursorLoader that will take care of
 90             // creating a Cursor for the data being displayed.
 91             String select = "((" + Contacts.DISPLAY_NAME + " NOTNULL) AND ("
 92                     + Contacts.HAS_PHONE_NUMBER + "=1) AND ("
 93                     + Contacts.DISPLAY_NAME + " != '' ))";
 94             //返回的是对这个数据源的监控
 95             return new CursorLoader(getActivity(), baseUri,
 96                     CONTACTS_SUMMARY_PROJECTION, select, null,
 97                     Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC");
 98         }
 99 
100         //每次数据源都有更新的时候,就会回调这个方法,然后update 我们的ui了。
101         public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
103 
104             // Swap the new cursor in.  (The framework will take care of closing the
105             // old cursor once we return.)
106             mAdapter.swapCursor(data);
107 
108             // The list should now be shown.
109             if (isResumed()) {
110                 setListShown(true);
111             } else {
112                 setListShownNoAnimation(true);
113             }
114         }
115 
116         public void onLoaderReset(Loader<Cursor> loader) {
117             // This is called when the last Cursor provided to onLoadFinished()
118             // above is about to be closed.  We need to make sure we are no
119             // longer using it.
120             mAdapter.swapCursor(null);
121         }
122     }
123 
124 }

可以仔细的观察一下这个代码,我们能发现 使用loader所需要的一些步骤:

1.需要一个activity或者是fragment,当然在上述的例子里 我们使用的是fragment。

2.一个LoaderManger的实例,注意看53行,我们get了一个loadermanager。这个地方就是获取实例了。

3.需要一个CursorLoader,并且从contentProvider获取数据源,90-97行 就是这么做的。

4.需要实现一个LoaderCallBack的这个接口,然后在几个回调方法里 写上我们自己业务的逻辑 即可。你看34行就是继承的接口。

还有3个回调方法在那,我们都在里面实现了自己的逻辑。

 

到这,其实一看,思路还是很清晰的。那到这里 有人肯定要说了。你这个没用啊,要实现contentprovider,我们的app不需要做

数据共享的,能否直接操作数据库呢?答案是可以的。在这里我们也可以构造出一个场景。假设有一张学生表。我们点击add

按钮,就自动往这个表里面增加一个数据,然后下面有个listview 会自动捕捉到 这个数据源的变化,然后自动更新列表。

我们可以知道 上面那个demo里面 CursorLoader的定义是这样的

1 public class CursorLoader extends AsyncTaskLoader<Cursor> {

我们现在要实现一个不用contentProvider的Loader 也是基于AsyncTaskLoader来的。

先给出一个抽象类:

 1 package com.example.administrator.activeandroidtest3;
 2 
 3 
 4 import android.content.AsyncTaskLoader;
 5 import android.content.Context;
 6 import android.database.Cursor;
 7 
 8 
 9 public abstract class SimpleCursorLoader extends AsyncTaskLoader<Cursor> {
10     private Cursor mCursor;
11 
12     public SimpleCursorLoader(Context context) {
13         super(context);
14     }
15 
16     /* 在子线程里运作 */
17     @Override
18     public abstract Cursor loadInBackground();
19 
20     /* 在ui 线程里运作 */
21     @Override
22     public void deliverResult(Cursor cursor) {
23         if (isReset()) {
24             // An async query came in while the loader is stopped
25             if (cursor != null) {
26                 cursor.close();
27             }
28             return;
29         }
30         Cursor oldCursor = mCursor;
31         mCursor = cursor;
32 
33         if (isStarted()) {
34             super.deliverResult(cursor);
35         }
36 
37         if (oldCursor != null && oldCursor != cursor && !oldCursor.isClosed()) {
38             oldCursor.close();
39         }
40     }
41 
42     @Override
43     protected void onStartLoading() {
44         if (mCursor != null) {
45             deliverResult(mCursor);
46         }
47         if (takeContentChanged() || mCursor == null) {
48             forceLoad();
49         }
50     }
51 
52     @Override
53     protected void onStopLoading() {
54         cancelLoad();
55     }
56 
57     @Override
58     public void onCanceled(Cursor cursor) {
59         if (cursor != null && !cursor.isClosed()) {
60             cursor.close();
61         }
62     }
63 
64     @Override
65     protected void onReset() {
66         super.onReset();
67 
68         onStopLoading();
69 
70         if (mCursor != null && !mCursor.isClosed()) {
71             mCursor.close();
72         }
73         mCursor = null;
74     }
75 }

然后我们再接着定义我们最终的 不需要provider的loader实现类(注意你如果想写的比较完美的话 cursor记得用抽象类的,抽象类的那个就不要写成private的了,我这里为了图简单 直接用自己构造的)。

 1 package com.example.administrator.activeandroidtest3;
 2 
 3 import android.content.Context;
 4 import android.database.Cursor;
 5 import android.database.sqlite.SQLiteDatabase;
 6 
 7 /**
 8  * Created by Administrator on 2015/10/7.
 9  */
10 public class SpecialLoader extends SimpleCursorLoader {
11 
12     ForceLoadContentObserver mObserver = new ForceLoadContentObserver();
13     private Context context;
14 
15     public SpecialLoader(Context context) {
16         super(context);
17         this.context = context;
18 
19     }
20 
21     @Override
22     public Cursor loadInBackground() {
23         DatabaseHelper dh = new DatabaseHelper(context, "Test.db");
24         SQLiteDatabase database = dh.getReadableDatabase();
25         String table = "Student";
26         String[] columns = new String[]{"Name", "No"};
27         //这个地方因为我用的是activeandroid 的orm 框架,所以默认的自增长主键是Id,但是SimpleCursorAdapter
28         //需要的是_id 否则会报错,所以这里要重命名一下
29         Cursor cursor = database.rawQuery("SELECT Id AS _id,Name,No FROM Student", null);
30         if (database != null) {
31             if (cursor != null) {
32                 //注册一下这个观察者
33                 cursor.registerContentObserver(mObserver);
34                 //这边也要注意 一定要监听这个uri的变化。但是如果你这个uri没有对应的provider的话
35                 //记得在你操作数据库的时候 通知一下这个uri
36                 cursor.setNotificationUri(context.getContentResolver(), MainActivity.uri);
37             }
38 
39         }
40         return cursor;
41     }
42 }

然后我们在简单看下activity 主类里的代码:

  1 package com.example.administrator.activeandroidtest3;
  2 
  3 import android.app.Activity;
  4 import android.app.LoaderManager;
  5 import android.content.Loader;
  6 import android.database.Cursor;
  7 import android.net.Uri;
  8 import android.os.Bundle;
  9 import android.util.Log;
 10 import android.view.Menu;
 11 import android.view.MenuItem;
 12 import android.view.View;
 13 import android.widget.ListView;
 14 import android.widget.SimpleCursorAdapter;
 15 import android.widget.TextView;
 16 
 17 import com.activeandroid.query.Select;
 18 
 19 import java.util.List;
 20 import java.util.Random;
 21 
 22 public class MainActivity extends Activity implements LoaderManager.LoaderCallbacks {
 23 
 24     public static final Uri uri = Uri.parse("content://com.example.student");
 25     private TextView addTv;
 26     private ListView lv;
 27     private SimpleCursorAdapter adapter;
 28 
 29     @Override
 30     protected void onCreate(Bundle savedInstanceState) {
 31         super.onCreate(savedInstanceState);
 32         setContentView(R.layout.activity_main);
 33         addTv = (TextView) this.findViewById(R.id.add);
 34         addTv.setOnClickListener(new View.OnClickListener() {
 35             @Override
 36             public void onClick(View v) {
 37                 Student student = new Student();
 38                 student.name = getRandomString(5);
 39                 student.no = (int) (Math.random() * 1000) + "";
 40                 student.sex = (int) (Math.random() * 1);
 41                 student.save();
 42                 //操作完数据库要notify 不然loader那边收不到哦
 43                 getContentResolver().notifyChange(uri, null);
 44 
 45             }
 46         });
 47         lv = (ListView) this.findViewById(R.id.lv);
 48         adapter = new SimpleCursorAdapter(MainActivity.this,
 49                 android.R.layout.simple_list_item_2, null,
 50                 new String[]{"Name", "No"},
 51                 new int[]{android.R.id.text1, android.R.id.text2}, 0);
 52         lv.setAdapter(adapter);
 53         getLoaderManager().initLoader(0, null, this);
 54     }
 55 
 56     @Override
 57     public boolean onCreateOptionsMenu(Menu menu) {
 58         // Inflate the menu; this adds items to the action bar if it is present.
 59         getMenuInflater().inflate(R.menu.menu_main, menu);
 60         return true;
 61     }
 62 
 63     @Override
 64     public boolean onOptionsItemSelected(MenuItem item) {
 65         // Handle action bar item clicks here. The action bar will
 66         // automatically handle clicks on the Home/Up button, so long
 67         // as you specify a parent activity in AndroidManifest.xml.
 68         int id = item.getItemId();
 69 
 70         //noinspection SimplifiableIfStatement
 71         if (id == R.id.action_settings) {
 72             return true;
 73         }
 74 
 75         return super.onOptionsItemSelected(item);
 76     }
 77 
 78 
 79     public static String getRandomString(int length) { //length表示生成字符串的长度
 80         String base = "abcdefghijklmnopqrstuvwxyz0123456789";
 81         Random random = new Random();
 82         StringBuffer sb = new StringBuffer();
 83         for (int i = 0; i < length; i++) {
 84             int number = random.nextInt(base.length());
 85             sb.append(base.charAt(number));
 86         }
 87         return sb.toString();
 88     }
 89 
 90 
 91     @Override
 92     public Loader onCreateLoader(int id, Bundle args) {
 93         SpecialLoader loader = new SpecialLoader(MainActivity.this);
 94         return loader;
 95     }
 96 
 97     @Override
 98     public void onLoadFinished(Loader loader, Object data) {
 99         adapter.swapCursor((Cursor) data);
100     }
101 
102     @Override
103     public void onLoaderReset(Loader loader) {
104 
105     }
106 }

最后我们看下运行的效果:

 

 

 

 好,那到这里 又有人要说了,你这个说来说去 还不是只能支持provider或者db类型的数据源吗?好 接着往下,

我们给出另外一个例子,不过这个例子是谷歌官方的例子,我就取其中重要的部分给予注释讲解。

http://developer.android.com/intl/zh-cn/reference/android/content/AsyncTaskLoader.html

首先说一下 这个例子是干嘛的,他主要是监听手机里app list的变化,比如你删除了一个应用

安装了一个应用,马上就能捕捉到你的手机里app list的变化 并显示在界面,大家都知道 监听app list

是通过监听系统广播来完成的。 我就主要讲一下 这个官方demo里 是如何在监听到系统广播以后和loader结合起来

然后自动回调方法的。

 1 /**
 2  * Helper class to look for interesting changes to the installed apps
 3  * so that the loader can be updated.
 4  */
 5 public static class PackageIntentReceiver extends BroadcastReceiver {
 6     final AppListLoader mLoader;
 7 
 8     //这个构造函数是很重要的 他接收的 就是自定义的loader
 9     public PackageIntentReceiver(AppListLoader loader) {
10         mLoader = loader;
11         IntentFilter filter = new IntentFilter(Intent.ACTION_PACKAGE_ADDED);
12         filter.addAction(Intent.ACTION_PACKAGE_REMOVED);
13         filter.addAction(Intent.ACTION_PACKAGE_CHANGED);
14         filter.addDataScheme("package");
15         mLoader.getContext().registerReceiver(this, filter);
16         // Register for events related to sdcard installation.
17         IntentFilter sdFilter = new IntentFilter();
18         sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE);
19         sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);
20         //在这个地方 直接用loader来注册这个广播接收器
21         mLoader.getContext().registerReceiver(this, sdFilter);
22     }
23 
24     //在收到广播以后 什么事情都没有做,而是调用了loader的onContentChanged方法
25     @Override public void onReceive(Context context, Intent intent) {
26         // Tell the loader about the change.
27         mLoader.onContentChanged();
28     }
29 }

你看这里的25-26行 调用了 loader的onContentChanged方法。继续看下面的loader

  1 /**
  2  * A custom Loader that loads all of the installed applications.
  3  */
  4 public static class AppListLoader extends AsyncTaskLoader<List<AppEntry>> {
  5     final InterestingConfigChanges mLastConfig = new InterestingConfigChanges();
  6     final PackageManager mPm;
  7 
  8     List<AppEntry> mApps;
  9     PackageIntentReceiver mPackageObserver;
 10 
 11     public AppListLoader(Context context) {
 12         super(context);
 13 
 14         // Retrieve the package manager for later use; note we don't
 15         // use 'context' directly but instead the save global application
 16         // context returned by getContext().
 17         mPm = getContext().getPackageManager();
 18     }
 19 
 20     //实际上最重要的就是这个方法了,每当这个回调方法被调用的时候 就去取applist 然后将结果返回到
 21     //onLoadFinished 这个回调方法里面!
 22     @Override public List<AppEntry> loadInBackground() {
 23         // Retrieve all known applications.
 24         List<ApplicationInfo> apps = mPm.getInstalledApplications(
 25                 PackageManager.GET_UNINSTALLED_PACKAGES |
 26                 PackageManager.GET_DISABLED_COMPONENTS);
 27         if (apps == null) {
 28             apps = new ArrayList<ApplicationInfo>();
 29         }
 30 
 31         final Context context = getContext();
 32 
 33         // Create corresponding array of entries and load their labels.
 34         List<AppEntry> entries = new ArrayList<AppEntry>(apps.size());
 35         for (int i=0; i<apps.size(); i++) {
 36             AppEntry entry = new AppEntry(this, apps.get(i));
 37             entry.loadLabel(context);
 38             entries.add(entry);
 39         }
 40 
 41         // Sort the list.
 42         Collections.sort(entries, ALPHA_COMPARATOR);
 43 
 44         // Done!
 45         return entries;
 46     }
 47 
 48     /**
 49      * Called when there is new data to deliver to the client.  The
 50      * super class will take care of delivering it; the implementation
 51      * here just adds a little more logic.
 52      */
 53     @Override public void deliverResult(List<AppEntry> apps) {
 54         if (isReset()) {
 55             // An async query came in while the loader is stopped.  We
 56             // don't need the result.
 57             if (apps != null) {
 58                 onReleaseResources(apps);
 59             }
 60         }
 61         List<AppEntry> oldApps = mApps;
 62         mApps = apps;
 63 
 64         if (isStarted()) {
 65             // If the Loader is currently started, we can immediately
 66             // deliver its results.
 67             super.deliverResult(apps);
 68         }
 69 
 70         // At this point we can release the resources associated with
 71         // 'oldApps' if needed; now that the new result is delivered we
 72         // know that it is no longer in use.
 73         if (oldApps != null) {
 74             onReleaseResources(oldApps);
 75         }
 76     }
 77 
 78     /**
 79      * Handles a request to start the Loader.
 80      */
 81     @Override protected void onStartLoading() {
 82         if (mApps != null) {
 83             // If we currently have a result available, deliver it
 84             // immediately.
 85             deliverResult(mApps);
 86         }
 87 
 88         // Start watching for changes in the app data.
 89         if (mPackageObserver == null) {
 90             mPackageObserver = new PackageIntentReceiver(this);
 91         }
 92 
 93         // Has something interesting in the configuration changed since we
 94         // last built the app list?
 95         boolean configChange = mLastConfig.applyNewConfig(getContext().getResources());
 96 
 97         if (takeContentChanged() || mApps == null || configChange) {
 98             // If the data has changed since the last time it was loaded
 99             // or is not currently available, start a load.
100             forceLoad();
101         }
102     }
103 
104     /**
105      * Handles a request to stop the Loader.
106      */
107     @Override protected void onStopLoading() {
108         // Attempt to cancel the current load task if possible.
109         cancelLoad();
110     }
111 
112     /**
113      * Handles a request to cancel a load.
114      */
115     @Override public void onCanceled(List<AppEntry> apps) {
116         super.onCanceled(apps);
117 
118         // At this point we can release the resources associated with 'apps'
119         // if needed.
120         onReleaseResources(apps);
121     }
122 
123     /**
124      * Handles a request to completely reset the Loader.
125      */
126     @Override protected void onReset() {
127         super.onReset();
128 
129         // Ensure the loader is stopped
130         onStopLoading();
131 
132         // At this point we can release the resources associated with 'apps'
133         // if needed.
134         if (mApps != null) {
135             onReleaseResources(mApps);
136             mApps = null;
137         }
138 
139         // Stop monitoring for changes.
140         if (mPackageObserver != null) {
141             getContext().unregisterReceiver(mPackageObserver);
142             mPackageObserver = null;
143         }
144     }
145 
146     /**
147      * Helper function to take care of releasing resources associated
148      * with an actively loaded data set.
149      */
150     protected void onReleaseResources(List<AppEntry> apps) {
151         // For a simple List<> there is nothing to do.  For something
152         // like a Cursor, we would close it here.
153     }
154 }

好,到这里流程就很明显了,在loader里 注册广播接收器,当广播接收器 收到广播以后 就调用loader的onContentChanged方法,

这个方法一调用 AppListLoader里的loadInBackGround就会被调用,然后当loadInBackGround执行完毕以后 就会把结果

传递给onLoadFinished方法了。 搞清楚这个流程 你就真正学会了使用loader这个大杀器了。当然了,我们并不满足于此,loader

还有一个特性就是可以自动管理他自己的生命周期 等等。我们现在就去看看他的源码,是如何完成这一点的。 并且上述几个方法

之间是如何相互调用的,顺序如何。

 

首先 我们要搞清楚几个类之间的关系:

1 public class CursorLoader extends AsyncTaskLoader<Cursor> {
2 
3 
4 public abstract class AsyncTaskLoader<D> extends Loader<D> {
5 
6 public class Loader<D> {

这样就很清晰。首先由一个实体类作为最基础的基类,Loader 注意他可以接受一个泛型为参数,然后有一个抽象类:AsyncTaskLoader 也是泛型作为参数。

最后实际调用运作的类就是CursorLoader类了,这里就可以看出来 传进去的泛型是一个Cursor。你在自定义Loader的时候,这个泛型参数 当然是可以自己决定的,

比如官方demo里 传的就是一个List。

搞清楚 他们三者之间的关系,剩下的就简单多了。可以逐步分析了。

在前面的3个demo里,我们分别演示了在fragment和activity里 调用loader的方法。 那我们就看看 这两者之间有什么异同点。先来看fragment。

fragment里 我们是这样调用的:

1  //这个地方初始化了我们的loader
2             getLoaderManager().initLoader(0, null, this);

直接get了一个manager 然后init他。我们进去看fragment的源码:

 1 //这边就能看出来一个fragment只能有一个loadermanager了。
 2 public LoaderManager getLoaderManager() {
 3 
 4         if (mLoaderManager != null) {
 5             return mLoaderManager;
 6         }
 7         //mHost很好理解 就是fragment的宿主,也就是跟fragment 相关联的activity。
 8         if (mHost == null) {
 9             throw new IllegalStateException("Fragment " + this + " not attached to Activity");
10         }
11         mCheckedForLoaderManager = true;
12         mLoaderManager = mHost.getLoaderManager(mWho, mLoadersStarted, true);
13         return mLoaderManager;
14     }

既然 我们知道 fragment的getLoaderManager也是通过activity的getLoader去调用的,那我们就去activity里的源码看看 :

 1   //在activty中最终实际上调用的就是他了 是这个方法
 2   LoaderManagerImpl getLoaderManagerImpl() {
 3         if (mLoaderManager != null) {
 4             return mLoaderManager;
 5         }
 6         mCheckedForLoaderManager = true;
 7         mLoaderManager = getLoaderManager("(root)", mLoadersStarted, true /*create*/);
 8         return mLoaderManager;
 9     }
10 
11 //这个地方就能看到 主要的第一个参数 who,你到这就能发现 如果是activity自己调用的话,传进去的who的值就是root
12 //也就是说一个actvity 只能有一个loadermanger 但是我们可以发现在fragment里 传进去的值是下面这个:
13 // Internal unique name for this fragment;
14 //String mWho;
15 //也就是说每一个fragment的mWho的值都是唯一的,而在activty中,是维护了一个map,一个key 对应一个loadermanager
16 //key就是fragment的那个唯一的标示,或者是activity自己,activity自己的标示就是(root)了
17     LoaderManagerImpl getLoaderManager(String who, boolean started, boolean create) {
18         if (mAllLoaderManagers == null) {
19             mAllLoaderManagers = new ArrayMap<String, LoaderManager>();
20         }
21         LoaderManagerImpl lm = (LoaderManagerImpl) mAllLoaderManagers.get(who);
22         if (lm == null) {
23             if (create) {
24                 lm = new LoaderManagerImpl(who, this, started);
25                 mAllLoaderManagers.put(who, lm);
26             }
27         } else {
28             lm.updateHostController(this);
29         }
30         return lm;
31     }

好 一直到这里 ,我们就可以下一个结论了,真正的loadermanager都是存储在activity中的,包括fragment的loadermanager也是,通过一个map来保证 get的时候

取的manager是自己对应的,并且全局唯一。继续往下看:

 1 public abstract class LoaderManager {
 2     /**
 3      * Callback interface for a client to interact with the manager.
 4      */
 5     public interface LoaderCallbacks<D> {
 6         /**
 7          * Instantiate and return a new Loader for the given ID.
 8          *
 9          * @param id The ID whose loader is to be created.
10          * @param args Any arguments supplied by the caller.
11          * @return Return a new Loader instance that is ready to start loading.
12          */
13         public Loader<D> onCreateLoader(int id, Bundle args);
14 
15         /**
16          * Called when a previously created loader has finished its load.  Note
17          * that normally an application is <em>not</em> allowed to commit fragment
18          * transactions while in this call, since it can happen after an
19          * activity's state is saved.  See {@link FragmentManager#beginTransaction()
20          * FragmentManager.openTransaction()} for further discussion on this.
21          * 
22          * <p>This function is guaranteed to be called prior to the release of
23          * the last data that was supplied for this Loader.  At this point
24          * you should remove all use of the old data (since it will be released
25          * soon), but should not do your own release of the data since its Loader
26          * owns it and will take care of that.  The Loader will take care of
27          * management of its data so you don't have to.  In particular:
28          *
29          * <ul>
30          * <li> <p>The Loader will monitor for changes to the data, and report
31          * them to you through new calls here.  You should not monitor the
32          * data yourself.  For example, if the data is a {@link android.database.Cursor}
33          * and you place it in a {@link android.widget.CursorAdapter}, use
34          * the {@link android.widget.CursorAdapter#CursorAdapter(android.content.Context,
35          * android.database.Cursor, int)} constructor <em>without</em> passing
36          * in either {@link android.widget.CursorAdapter#FLAG_AUTO_REQUERY}
37          * or {@link android.widget.CursorAdapter#FLAG_REGISTER_CONTENT_OBSERVER}
38          * (that is, use 0 for the flags argument).  This prevents the CursorAdapter
39          * from doing its own observing of the Cursor, which is not needed since
40          * when a change happens you will get a new Cursor throw another call
41          * here.
42          * <li> The Loader will release the data once it knows the application
43          * is no longer using it.  For example, if the data is
44          * a {@link android.database.Cursor} from a {@link android.content.CursorLoader},
45          * you should not call close() on it yourself.  If the Cursor is being placed in a
46          * {@link android.widget.CursorAdapter}, you should use the
47          * {@link android.widget.CursorAdapter#swapCursor(android.database.Cursor)}
48          * method so that the old Cursor is not closed.
49          * </ul>
50          *
51          * @param loader The Loader that has finished.
52          * @param data The data generated by the Loader.
53          */
54         public void onLoadFinished(Loader<D> loader, D data);
55 
56         /**
57          * Called when a previously created loader is being reset, and thus
58          * making its data unavailable.  The application should at this point
59          * remove any references it has to the Loader's data.
60          *
61          * @param loader The Loader that is being reset.
62          */
63         public void onLoaderReset(Loader<D> loader);
64     }

一看就知道 loadermanger 其实是一个抽象类。就是定义了一些 我们需要的接口而已,这些接口方法的含义和用法 在那3个demo里 相信大家都有了解,不多说。

我们去看看这个抽象类的实现类,为什么要看他,因为你在get到这个maganger以后 马上就去调用了他的init方法 我们就看看这部分的逻辑是怎么样的:

 1 public <D> Loader<D> initLoader(int id, Bundle args, LoaderManager.LoaderCallbacks<D> callback) {
 2         if (mCreatingLoader) {
 3             throw new IllegalStateException("Called while creating a loader");
 4         }
 5 
 6         //这个就是先看看是否有活动的loader 有的话就取出来 没有的话 就创建一个
 7         LoaderInfo info = mLoaders.get(id);
 8         
 9         if (DEBUG) Log.v(TAG, "initLoader in " + this + ": args=" + args);
10 
11         if (info == null) {
12             // Loader doesn't already exist; create.
13             info = createAndInstallLoader(id, args,  (LoaderManager.LoaderCallbacks<Object>)callback);
14             if (DEBUG) Log.v(TAG, "  Created new loader " + info);
15         } else {
16             if (DEBUG) Log.v(TAG, "  Re-using existing loader " + info);
17             info.mCallbacks = (LoaderManager.LoaderCallbacks<Object>)callback;
18         }
19         
20         if (info.mHaveData && mStarted) {
21             // If the loader has already generated its data, report it now.
22             info.callOnLoadFinished(info.mLoader, info.mData);
23         }
24         
25         return (Loader<D>)info.mLoader;
26     }
27 
28     //这个就是现在存活的loader
29     final SparseArray<LoaderInfo> mLoaders = new SparseArray<LoaderInfo>(0);
30 
31     //这个是已经运行结束的loader
32     final SparseArray<LoaderInfo> mInactiveLoaders = new SparseArray<LoaderInfo>(0);
33 
34     //其实这个创建loader的过程特别简单,我们主要看第三个参数,callback 这个参数
35     //一想就明白,在前面3个demo里我们是直接在fragemet和activity里实现的callback
36     //所以传进去的就是this,也就是说 回调就是在这个函数里 真正的和loader 发生了关联了
37     private LoaderInfo createAndInstallLoader(int id, Bundle args,
38             LoaderManager.LoaderCallbacks<Object> callback) {
39         try {
40             mCreatingLoader = true;
41             LoaderInfo info = createLoader(id, args, callback);
42             installLoader(info);
43             return info;
44         } finally {
45             mCreatingLoader = false;
46         }
47     }

你看 一直到这里,我们就明白了 callback是怎么和loadermageer本身发生关联的。 我们继续往下看。这次我们要搞明白

当数据源发生变化的时候 是怎么一步步回调我们子类loader的方法的。

我们先看Loader这个基类的主要方法:

 1  
 2 
 3 //这个是一个观察者 当发生变化的时候 他调用了onContentChanged方法
 4  public final class ForceLoadContentObserver extends ContentObserver {
 5         public ForceLoadContentObserver() {
 6             super(new Handler());
 7         }
 8 
 9         @Override
10         public boolean deliverSelfNotifications() {
11             return true;
12         }
13 
14         @Override
15         public void onChange(boolean selfChange) {
16             onContentChanged();
17         }
18     }
19 
20 //下面这2个方法一看就明白 最终当数据源发生变化的时候 会通知这个观察者,然后这个观察者会最终调用
21 //onForceLoad这个方法 而onForceLoad是交给子类去实现的 也就是AsyncTaskLoader的onForceLoad方法了
22 public void onContentChanged() {
23         if (mStarted) {
24             forceLoad();
25         } else {
26             // This loader has been stopped, so we don't want to load
27             // new data right now...  but keep track of it changing to
28             // refresh later if we start again.
29             mContentChanged = true;
30         }
31     }
32 
33  public void forceLoad() {
34         onForceLoad();
35     }
36 
37     /**
38      * Subclasses must implement this to take care of requests to {@link #forceLoad()}.
39      * This will always be called from the process's main thread.
40      */
41     protected void onForceLoad() {
42     }

然后看看AsyncTaskLoader的几个主要方法:

 1 //这边一目了然 asynacTaskLoader 里面 正好是有一个AsyncTask对象的!实现了runnabele接口
 2 //注意着参数d 这个d是干嘛的,这个d就是用来传递参数的一个泛型,可以是系统实现的loader里的cursor
 3 //也可以是我们自己实现的loader里的list类型
 4 final class LoadTask extends AsyncTask<Void, Void, D> implements Runnable {
 5         private final CountDownLatch mDone = new CountDownLatch(1);
 6 
 7         // Set to true to indicate that the task has been posted to a handler for
 8         // execution at a later time.  Used to throttle updates.
 9         boolean waiting;
10 
11         /* Runs on a worker thread */
12         @Override
13         protected D doInBackground(Void... params) {
14             if (DEBUG) Log.v(TAG, this + " >>> doInBackground");
15             try {
16                 //这个地方就很明显了,他调用了自己的onLoadInBackGround方法
17                 D data = AsyncTaskLoader.this.onLoadInBackground();
18                 if (DEBUG) Log.v(TAG, this + "  <<< doInBackground");
19                 return data;
20             } catch (OperationCanceledException ex) {
21                 if (!isCancelled()) {
22                     // onLoadInBackground threw a canceled exception spuriously.
23                     // This is problematic because it means that the LoaderManager did not
24                     // cancel the Loader itself and still expects to receive a result.
25                     // Additionally, the Loader's own state will not have been updated to
26                     // reflect the fact that the task was being canceled.
27                     // So we treat this case as an unhandled exception.
28                     throw ex;
29                 }
30                 if (DEBUG) Log.v(TAG, this + "  <<< doInBackground (was canceled)", ex);
31                 return null;
32             }
33         }
34         //后面还有很多代码 略过
35 }
36 
37 //你看这里下面的2个函数 一看就明白了 最终task里调用的是这个抽象方法,那这个抽象方法
38 //就是留给我们子类自己去实现的,我们在自定义loader的时候最重要的就是重写这个方法。
39  protected D onLoadInBackground() {
40         return loadInBackground();
41     }
42 
43  public abstract D loadInBackground();
44 
45 //你看这个地方 就是当数据源发生变化的时候 就会调用这个方法了,启动了我们的laodtask 
46 //也是最终调用子类 也就是CursorLoader这样的子类的loadInBackground方法了
47 @Override
48     protected void onForceLoad() {
49         super.onForceLoad();
50         cancelLoad();
51         mTask = new LoadTask();
52         if (DEBUG) Log.v(TAG, "Preparing load: mTask=" + mTask);
53         executePendingTask();
54     }

相信到这里 大家一定能搞明白数据源变化的时候 是怎么一步步调用我们的loader里的回调方法的,那有人肯定要继续问

当你这个方法调用完毕的时候 是怎么通知最后updateUI呢,也就是当你background方法结束以后是怎么调用的

onLoadFinished方法的呢?

我们继续看AsyncTaskLoader这个类

 1  
 2  //在那个asynctask里面 走完是肯定要走这个方法的 相信大家都能理解。
 3         @Override
 4         protected void onPostExecute(D data) {
 5             if (DEBUG) Log.v(TAG, this + " onPostExecute");
 6             try {
 7                 AsyncTaskLoader.this.dispatchOnLoadComplete(this, data);
 8             } finally {
 9                 mDone.countDown();
10             }
11         }
12 //实际上走的就是这个方法。看26行-
13         void dispatchOnLoadComplete(LoadTask task, D data) {
14         if (mTask != task) {
15             if (DEBUG) Log.v(TAG, "Load complete of old task, trying to cancel");
16             dispatchOnCancelled(task, data);
17         } else {
18             if (isAbandoned()) {
19                 // This cursor has been abandoned; just cancel the new data.
20                 onCanceled(data);
21             } else {
22                 commitContentChanged();
23                 mLastLoadCompleteTime = SystemClock.uptimeMillis();
24                 mTask = null;
25                 if (DEBUG) Log.v(TAG, "Delivering result");
26                 deliverResult(data);
27             }
28         }
29     }
30 
31 //这边一下就看出来是调用的mListtenr的回调方法
32      public void deliverResult(D data) {
33         if (mListener != null) {
34             mListener.onLoadComplete(this, data);
35         }
36     }

实际上这个Listener就是在Loader这个基类里:

 1     OnLoadCompleteListener<D> mListener;
 2 
 3 public interface OnLoadCompleteListener<D> {
 4         /**
 5          * Called on the thread that created the Loader when the load is complete.
 6          *
 7          * @param loader the loader that completed the load
 8          * @param data the result of the load
 9          */
10         public void onLoadComplete(Loader<D> loader, D data);
11     }
12 
13 //并且通过这个注册
14  public void registerListener(int id, OnLoadCompleteListener<D> listener) {
15         if (mListener != null) {
16             throw new IllegalStateException("There is already a listener registered");
17         }
18         mListener = listener;
19         mId = id;
20     }

那就好了 我们就是要看一下 是在哪个地方调用的registerlistener这个方法 注册他的

  1   
  2 //回到initLoader的这个方法 注意这个方法是在LoaderManger里面
  3   public <D> Loader<D> initLoader(int id, Bundle args, LoaderManager.LoaderCallbacks<D> callback) {
  4         if (mCreatingLoader) {
  5             throw new IllegalStateException("Called while creating a loader");
  6         }
  7         
  8         LoaderInfo info = mLoaders.get(id);
  9         
 10         if (DEBUG) Log.v(TAG, "initLoader in " + this + ": args=" + args);
 11 
 12         if (info == null) {
 13 //下面的代码跳转到30行
 14             info = createAndInstallLoader(id, args,  (LoaderManager.LoaderCallbacks<Object>)callback);
 15             if (DEBUG) Log.v(TAG, "  Created new loader " + info);
 16         } else {
 17             if (DEBUG) Log.v(TAG, "  Re-using existing loader " + info);
 18             info.mCallbacks = (LoaderManager.LoaderCallbacks<Object>)callback;
 19         }
 20         
 21         if (info.mHaveData && mStarted) {
 22             // If the loader has already generated its data, report it now.
 23             info.callOnLoadFinished(info.mLoader, info.mData);
 24         }
 25         
 26         return (Loader<D>)info.mLoader;
 27     }
 28     
 29 
 30     private LoaderInfo createAndInstallLoader(int id, Bundle args,
 31             LoaderManager.LoaderCallbacks<Object> callback) {
 32         try {
 33             mCreatingLoader = true;
 34             LoaderInfo info = createLoader(id, args, callback);
 35             //这里跳转到43行
 36             installLoader(info);
 37             return info;
 38         } finally {
 39             mCreatingLoader = false;
 40         }
 41     }
 42 
 43     void installLoader(LoaderInfo info) {
 44         mLoaders.put(info.mId, info);
 45         if (mStarted) {
 46             //跳转到51行
 47             info.start();
 48         }
 49     }
 50 
 51    void start() {
 52             if (mRetaining && mRetainingStarted) {
 53                 // Our owner is started, but we were being retained from a
 54                 // previous instance in the started state...  so there is really
 55                 // nothing to do here, since the loaders are still started.
 56                 mStarted = true;
 57                 return;
 58             }
 59 
 60             if (mStarted) {
 61                 // If loader already started, don't restart.
 62                 return;
 63             }
 64 
 65             mStarted = true;
 66             
 67             if (DEBUG) Log.v(TAG, "  Starting: " + this);
 68             if (mLoader == null && mCallbacks != null) {
 69                mLoader = mCallbacks.onCreateLoader(mId, mArgs);
 70             }
 71             if (mLoader != null) {
 72                 if (mLoader.getClass().isMemberClass()
 73                         && !Modifier.isStatic(mLoader.getClass().getModifiers())) {
 74                     throw new IllegalArgumentException(
 75                             "Object returned from onCreateLoader must not be a non-static inner member class: "
 76                             + mLoader);
 77                 }
 78                 if (!mListenerRegistered) {
 79                     //就是在这里注册的mloader里的回调了,注意这里的参数是this 也就是loaderInfo这个类 注意这个类就是loadermanger里的内部类了 再继续往下看
 80                     //我们前面说到 在asynctask里面最终调用的是mLoader里的onLoadComplete方法 所以我们就看看loaderInfo这个类里的这个方法做了什么看91行
 81                     mLoader.registerListener(mId, this);
 82                     mLoader.registerOnLoadCanceledListener(this);
 83                     mListenerRegistered = true;
 84                 }
 85                 mLoader.startLoading();
 86             }
 87         }
 88 
 89 
 90 
 91          @Override
 92         public void onLoadComplete(Loader<Object> loader, Object data) {
 93             if (DEBUG) Log.v(TAG, "onLoadComplete: " + this);
 94             
 95             if (mDestroyed) {
 96                 if (DEBUG) Log.v(TAG, "  Ignoring load complete -- destroyed");
 97                 return;
 98             }
 99 
100             if (mLoaders.get(mId) != this) {
101                 // This data is not coming from the current active loader.
102                 // We don't care about it.
103                 if (DEBUG) Log.v(TAG, "  Ignoring load complete -- not active");
104                 return;
105             }
106             
107             LoaderInfo pending = mPendingLoader;
108             if (pending != null) {
109                 // There is a new request pending and we were just
110                 // waiting for the old one to complete before starting
111                 // it.  So now it is time, switch over to the new loader.
112                 if (DEBUG) Log.v(TAG, "  Switching to pending loader: " + pending);
113                 mPendingLoader = null;
114                 mLoaders.put(mId, null);
115                 destroy();
116                 installLoader(pending);
117                 return;
118             }
119             
120             // Notify of the new data so the app can switch out the old data before
121             // we try to destroy it.
122             if (mData != data || !mHaveData) {
123                 mData = data;
124                 mHaveData = true;
125                 if (mStarted) {
126                     //继续往下 看第149行 
127                     callOnLoadFinished(loader, data);
128                 }
129             }
130 
131             //if (DEBUG) Log.v(TAG, "  onLoadFinished returned: " + this);
132 
133             // We have now given the application the new loader with its
134             // loaded data, so it should have stopped using the previous
135             // loader.  If there is a previous loader on the inactive list,
136             // clean it up.
137             LoaderInfo info = mInactiveLoaders.get(mId);
138             if (info != null && info != this) {
139                 info.mDeliveredData = false;
140                 info.destroy();
141                 mInactiveLoaders.remove(mId);
142             }
143 
144             if (mHost != null && !hasRunningLoaders()) {
145                 mHost.mFragmentManager.startPendingDeferredFragments();
146             }
147         }
148 
149          void callOnLoadFinished(Loader<Object> loader, Object data) {
150             if (mCallbacks != null) {
151                 String lastBecause = null;
152                 if (mHost != null) {
153                     lastBecause = mHost.mFragmentManager.mNoTransactionsBecause;
154                     mHost.mFragmentManager.mNoTransactionsBecause = "onLoadFinished";
155                 }
156                 try {
157                     if (DEBUG) Log.v(TAG, "  onLoadFinished in " + loader + ": "
158                             + loader.dataToString(data));
159                     //到这里就真相大白了,最终callback是在这里调用的onLoadFinished方法也就是我们经常重写的方法
160                     mCallbacks.onLoadFinished(loader, data);
161                 } finally {
162                     if (mHost != null) {
163                         mHost.mFragmentManager.mNoTransactionsBecause = lastBecause;
164                     }
165                 }
166                 mDeliveredData = true;
167             }
168         }

好,到这里 我们就把Loader框架中的 数据传递 整个流程给摸清楚了。最后我们再来看看 他的生命周期是如何管理的吧。

我们可以先看看activity的:

  1 //看activity的onStart方法
  2 protected void onStart() {
  3         if (DEBUG_LIFECYCLE) Slog.v(TAG, "onStart " + this);
  4         mCalled = true;
  5         //继续看12行 这个地方mFragements 你就理解成activity本身即可,不多做解释 这个地方要搞清楚 又是另外一块了 有兴趣的可以自行谷歌activity和fragment如何建立关系
  6         mFragments.doLoaderStart();
  7 
  8         getApplication().dispatchActivityStarted(this);
  9     }
 10 
 11     //这个函数就很明显了 调用了manager的dostart函数
 12      void doLoaderStart() {
 13         if (mLoadersStarted) {
 14             return;
 15         }
 16         mLoadersStarted = true;
 17 
 18         if (mLoaderManager != null) {
 19             //跳转到30行
 20             mLoaderManager.doStart();
 21         } else if (!mCheckedForLoaderManager) {
 22             mLoaderManager = getLoaderManager("(root)", mLoadersStarted, false);
 23         }
 24         mCheckedForLoaderManager = true;
 25     }
 26 
 27 //------------------注意上面的代码都在activity里,下面的开始 都在LoaderManger类里了
 28 
 29      void doStart() {
 30         if (DEBUG) Log.v(TAG, "Starting in " + this);
 31         if (mStarted) {
 32             RuntimeException e = new RuntimeException("here");
 33             e.fillInStackTrace();
 34             Log.w(TAG, "Called doStart when already started: " + this, e);
 35             return;
 36         }
 37         
 38         mStarted = true;
 39 
 40         // Call out to sub classes so they can start their loaders
 41         // Let the existing loaders know that we want to be notified when a load is complete
 42         for (int i = mLoaders.size()-1; i >= 0; i--) {
 43             //跳转到50行
 44             mLoaders.valueAt(i).start();
 45         }
 46     }
 47 
 48 
 49      void start() {
 50             if (mRetaining && mRetainingStarted) {
 51                 // Our owner is started, but we were being retained from a
 52                 // previous instance in the started state...  so there is really
 53                 // nothing to do here, since the loaders are still started.
 54                 mStarted = true;
 55                 return;
 56             }
 57 
 58             if (mStarted) {
 59                 // If loader already started, don't restart.
 60                 return;
 61             }
 62 
 63             mStarted = true;
 64             
 65             if (DEBUG) Log.v(TAG, "  Starting: " + this);
 66             if (mLoader == null && mCallbacks != null) {
 67                 //原来onCreateLoader这个回调方法 是在这里调用的 怪不得谷歌说这个方法是必定会被执行并且只会被执行一次的方法!
 68                mLoader = mCallbacks.onCreateLoader(mId, mArgs);
 69             }
 70             if (mLoader != null) {
 71                 if (mLoader.getClass().isMemberClass()
 72                         && !Modifier.isStatic(mLoader.getClass().getModifiers())) {
 73                     throw new IllegalArgumentException(
 74                             "Object returned from onCreateLoader must not be a non-static inner member class: "
 75                             + mLoader);
 76                 }
 77                 if (!mListenerRegistered) {
 78                     mLoader.registerListener(mId, this);
 79                     mLoader.registerOnLoadCanceledListener(this);
 80                     mListenerRegistered = true;
 81                 }
 82                 //你看这里调用了startLoading方法 这个方法是属于mLoader的 跳转到88行
 83                 mLoader.startLoading();
 84             }
 85         }
 86 
 87 //88- 98行是loader这个类里的
 88     public final void startLoading() {
 89         mStarted = true;
 90         mReset = false;
 91         mAbandoned = false;
 92         onStartLoading();
 93     }
 94 
 95     //你看最终是调用的这个方法,注意他是空方法 是交给子类去实现的,我们去看看cursorloader这个子类是怎么实现的吧。
 96     protected void onStartLoading() {
 97     }
 98 //99-  112行 是cursorLoader这个类的代码
 99      
100 //你看这个地方 直接调用了forceload方法 这个方法大家前面肯定有印象  他最终会启动那个asynctask 去执行background方法
101 //这也就解释了 第一次我们的数据是怎么来的,比如说 假设我们的数据源还没有被更新的时候,为什么会自动去查找数据源 并返回数据
102 //到这里就明白了,原来是activity的onStart函数为开端 一步步走到Loader的子类的onStartLoading方法里的,当然你如果觉得
103 //Loader不需要初始加载 只要在有变化的时候再加载 那这个方法你就可以保持为空了。
104      protected void onStartLoading() {
105         if (mCursor != null) {
106             deliverResult(mCursor);
107         }
108         if (takeContentChanged() || mCursor == null) {
109             forceLoad();
110         }
111     }
112 
113 //114-139行 为 http://developer.android.com/intl/zh-cn/reference/android/content/AsyncTaskLoader.html 这个里面 AppListLoader  的一段源码
114 //你看138行 也是直接调用的forceLoad 这样当我们的applist没有变化的时候 第一次也能显示出列表 
115  /**
116      * Handles a request to start the Loader.
117      */
118     @Override protected void onStartLoading() {
119         if (mApps != null) {
120             // If we currently have a result available, deliver it
121             // immediately.
122             deliverResult(mApps);
123         }
124 
125         // Start watching for changes in the app data.
126         if (mPackageObserver == null) {
127             mPackageObserver = new PackageIntentReceiver(this);
128         }
129 
130         // Has something interesting in the configuration changed since we
131         // last built the app list?
132         boolean configChange = mLastConfig.applyNewConfig(getContext().getResources());
133 
134         if (takeContentChanged() || mApps == null || configChange) {
135             // If the data has changed since the last time it was loaded
136             // or is not currently available, start a load.
137             forceLoad();
138         }
139     }

start流程 我们分析完毕了 最后我们再看看stop流程吧 看完这个 其他生命周期 我们就不分析了留给读者自己感兴趣的话自己分析试试看。

  1 //我们来看看fragment的onDestroy方法 都做了什么
  2 public void onDestroy() {
  3         mCalled = true;
  4         //Log.v("foo", "onDestroy: mCheckedForLoaderManager=" + mCheckedForLoaderManager
  5         //        + " mLoaderManager=" + mLoaderManager);
  6         if (!mCheckedForLoaderManager) {
  7             mCheckedForLoaderManager = true;
  8             mLoaderManager = mHost.getLoaderManager(mWho, mLoadersStarted, false);
  9         }
 10         if (mLoaderManager != null) {
 11             //跳转到16行
 12             mLoaderManager.doDestroy();
 13         }
 14     }
 15 //上面的代码 是在fragment里 下面的代码在loadermanger里
 16      void doDestroy() {
 17         if (!mRetaining) {
 18             if (DEBUG) Log.v(TAG, "Destroying Active in " + this);
 19             for (int i = mLoaders.size()-1; i >= 0; i--) {
 20                 mLoaders.valueAt(i).destroy();
 21             }
 22             mLoaders.clear();
 23         }
 24         
 25         if (DEBUG) Log.v(TAG, "Destroying Inactive in " + this);
 26         for (int i = mInactiveLoaders.size()-1; i >= 0; i--) {
 27             mInactiveLoaders.valueAt(i).destroy();
 28         }
 29         mInactiveLoaders.clear();
 30     }
 31 //下面这个destroy流程 可以清晰的看到很多东西 包括clear所有回调等
 32  void destroy() {
 33             if (DEBUG) Log.v(TAG, "  Destroying: " + this);
 34             mDestroyed = true;
 35             boolean needReset = mDeliveredData;
 36             mDeliveredData = false;
 37             if (mCallbacks != null && mLoader != null && mHaveData && needReset) {
 38                 if (DEBUG) Log.v(TAG, "  Reseting: " + this);
 39                 String lastBecause = null;
 40                 if (mHost != null) {
 41                     lastBecause = mHost.mFragmentManager.mNoTransactionsBecause;
 42                     mHost.mFragmentManager.mNoTransactionsBecause = "onLoaderReset";
 43                 }
 44                 try {
 45                     mCallbacks.onLoaderReset(mLoader);
 46                 } finally {
 47                     if (mHost != null) {
 48                         mHost.mFragmentManager.mNoTransactionsBecause = lastBecause;
 49                     }
 50                 }
 51             }
 52             mCallbacks = null;
 53             mData = null;
 54             mHaveData = false;
 55             if (mLoader != null) {
 56                 if (mListenerRegistered) {
 57                     mListenerRegistered = false;
 58                     mLoader.unregisterListener(this);
 59                     mLoader.unregisterOnLoadCanceledListener(this);
 60                 }
 61                 //在这调用了rest
 62                 mLoader.reset();
 63             }
 64             if (mPendingLoader != null) {
 65                 mPendingLoader.destroy();
 66             }
 67         }
 68 //最后我们来看看loader里的代码 就能明白了 当fragement destroy的时候最终的调用来到了子类的onReset方法
 69          public void reset() {
 70         onReset();
 71         mReset = true;
 72         mStarted = false;
 73         mAbandoned = false;
 74         mContentChanged = false;
 75         mProcessingChange = false;
 76     }
 77 
 78     /**
 79      * Subclasses must implement this to take care of resetting their loader,
 80      * as per {@link #reset()}.  This is not called by clients directly,
 81      * but as a result of a call to {@link #reset()}.
 82      * This will always be called from the process's main thread.
 83      */
 84     protected void onReset() {
 85     }
 86 
 87 //这里是cURSORLOADER的代码了 你看这里关闭了cursor
 88     @Override
 89     protected void onReset() {
 90         super.onReset();
 91         
 92         // Ensure the loader is stopped
 93         onStopLoading();
 94 
 95         if (mCursor != null && !mCursor.isClosed()) {
 96             mCursor.close();
 97         }
 98         mCursor = null;
 99     }
100 
101 //同样的 我们也能看到applistloader源码里面 也是在这个函数里清除了广播接收器。
102 //所以读到这里 我们就知道 loader的强大了。你只需要搞清楚这些生命周期的函数的意义
103 //就可以重写他们,至于什么时候调用 loader都帮你做好了 你只需要在里面实现你自己的逻辑即可!非常强大 非常好用
104     @Override protected void onReset() {
105         super.onReset();
106 
107         // Ensure the loader is stopped
108         onStopLoading();
109 
110         // At this point we can release the resources associated with 'apps'
111         // if needed.
112         if (mApps != null) {
113             onReleaseResources(mApps);
114             mApps = null;
115         }
116 
117         // Stop monitoring for changes.
118         if (mPackageObserver != null) {
119             getContext().unregisterReceiver(mPackageObserver);
120             mPackageObserver = null;
121         }
122     }

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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posted @ 2015-10-08 16:16  希尔瓦娜斯女神  阅读(12057)  评论(3编辑  收藏  举报