Loader之二:CursorLoader基本实例 分类: H1_ANDROID 2013-11-16 10:50 5447人阅读 评论(0) 收藏
参考APIDEMO:sdk\samples\android-19\content\LoaderCursor
1、创建主布局文件,里面只包含一个Fragment。
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/FrameLayout1" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context=".MainActivity" > <fragment android:id="@+id/fragment_list" android:name="com.example.android.content.loadercursor.CursorLoaderListFragment" android:layout_width="match_parent" android:layout_height="match_parent" /> </FrameLayout>
2、创建主Activity文件中的android:name加载相应的Fragment
package com.example.android.content.loadercursor; import android.app.Activity; import android.app.ListFragment; import android.app.LoaderManager; import android.database.Cursor; import android.os.Bundle; import android.widget.SearchView; /** * The entry point to the CursorLoader sample. This sample demonstrates the use * of the {@link LoaderManager} to retrieve data from a {@link Cursor}. Here, a * list of contacts is displayed in a {@link ListFragment} and filtered using a * {@link SearchView} ActionBar item. */ public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } }
3、创建相应的Fragment
package com.example.android.content.loadercursor; import android.app.ListFragment; import android.app.LoaderManager; import android.content.CursorLoader; import android.content.Loader; import android.database.Cursor; import android.net.Uri; import android.os.Bundle; import android.provider.ContactsContract.Contacts; import android.view.View; import android.widget.ListView; import android.widget.SearchView; import android.widget.SimpleCursorAdapter; import android.widget.Toast; /** * A {@link ListFragment} that shows the use of a {@link LoaderManager} to * display a list of contacts accessed through a {@link Cursor}. */ /* * (1)继承Fragment或者其子类,用于创建一个Fragment。实现LoaderManager.LoaderCallbacks接口,用于与Loader的交互 * 。 官方文档: A callback interface for a client to interact with the LoaderManager. * For example, you use the onCreateLoader() callback method to create a new * loader. */ public class CursorLoaderListFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor> { // This is the Adapter being used to display the list's data. SimpleCursorAdapter mAdapter; // The SearchView for doing filtering. SearchView mSearchView; /* * (2)在Activity被创建时调用此方法。Called when the fragment's activity has been * created and this fragment's view hierarchy instantiated. You typically * initialize a Loader within the activity's onCreate() method, or within * the fragment's onActivityCreated() method. */@Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); // Give some text to display if there is no data. In a real // application this would come from a resource. setEmptyText("No phone numbers"); /* * Create an empty adapter we will use to display the loaded data. The * simple_list_item_2 layout contains two rows on top of each other * (text1 and text2) that will show the contact's name and status. */ // (3)设置Fragment的顯示內容 mAdapter = new SimpleCursorAdapter(getActivity(), android.R.layout.simple_list_item_2, null, new String[] { Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS }, new int[] { android.R.id.text1, android.R.id.text2 }, 0); setListAdapter(mAdapter); // Start out with a progress indicator. setListShown(false); // Prepare the loader. Either re-connect with an existing one, // or start a new one. /* * (4)創建一個Loader,此Loader用于為Fragment載入內容。You typically initialize a * Loader within the activity's onCreate() method, or within the * fragment's onActivityCreated() method. * 此方法將自動調用LoaderManager.LoaderCallbacks接口的onCreateLoader方法。 */ getLoaderManager().initLoader(0, null, this); } /** * An item has been clicked in the {@link ListView}. Display a toast with * the tapped item's id. */ @Override public void onListItemClick(ListView l, View v, int position, long id) { Toast.makeText(getActivity(), "Item clicked: " + id, Toast.LENGTH_LONG) .show(); } // These are the Contacts rows that we will retrieve. static final String[] CONTACTS_SUMMARY_PROJECTION = new String[] { Contacts._ID, Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS, Contacts.LOOKUP_KEY, }; /* * (5)Loader被創建時的操作,一般用于加載內容。In this example, the onCreateLoader() callback * method creates a CursorLoader. You must build the CursorLoader using its * constructor method, which requires the complete set of information needed * to perform a query to the ContentProvider. */public Loader<Cursor> onCreateLoader(int id, Bundle args) { // This is called when a new Loader needs to be created. This // sample only has one Loader, so we don't care about the ID. // First, pick the base URI to use depending on whether we are // currently filtering. Uri baseUri; baseUri = Contacts.CONTENT_URI; // Now create and return a CursorLoader that will take care of // creating a Cursor for the data being displayed. String select = "((" + Contacts.DISPLAY_NAME + " NOTNULL) AND (" + Contacts.HAS_PHONE_NUMBER + "=1) AND (" + Contacts.DISPLAY_NAME + " != '' ))"; String order = Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC"; return new CursorLoader(getActivity(), baseUri, CONTACTS_SUMMARY_PROJECTION, select, null, order); } /* * (6)内容被加载完成后的操作。The loader will release the data once it knows the * application is no longer using it. For example, if the data is a cursor * from a CursorLoader, you should not call close() on it yourself. If the * cursor is being placed in a CursorAdapter, you should use the * swapCursor() method so that the old Cursor is not closed. */public void onLoadFinished(Loader<Cursor> loader, Cursor data) { // Swap the new cursor in. (The framework will take care of closing the // old cursor once we return.) // Swap in a new Cursor, returning the old Cursor. Unlike // changeCursor(Cursor), the returned old Cursor is not closed. mAdapter.swapCursor(data); // The list should now be shown. if (isResumed()) { setListShown(true); } else { setListShownNoAnimation(true); } } // (7)Loader被重新加载时的操作。 public void onLoaderReset(Loader<Cursor> loader) { // This is called when the last Cursor provided to onLoadFinished() // above is about to be closed. We need to make sure we are no // longer using it. mAdapter.swapCursor(null); } }
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