Android高级编程（笔记）-第6章数据存储、检索和共享--1--共享Preference

三种技术：preference、本地文件和SQLite

一、Android中的数据保存技术：

共享的preference

文件

SQLite数制库

内容提供器

共享的preference

二、保存简单的应用程序数据

两种轻量级技术：共享的preference和用来保存活动实例细节的一对事件处理程序

用SharedPreference在应用程序中创建命名的键/值映射

活动提供SaveInstanceState处理程序，参数Bundle代表一个基本的键/值映射，其后这一参数传给OnCreate和onRestoreInstanceState方法处理程序，用以记录活动（Activity）需要的值

1、创建和保存preference

上下文调用getSharedPreference

SharedPreference.Editor类：修改一个共享preference。用法：在SharedPreference上调用edit得到一个编辑器对象，保存编辑，只需调用编辑器commit即可。

2、检索共享的Preference

使用getSharedPreference访问已经保存的共享Preference，通过传递给它希望访问的共享Preference的名称，并使用类型安全的get<type>方法来提取已保存的值

3、保存活动状态

Activity.getPrefrence():不指定名字，保存不需要和其它组件进行共享的活动信息(如类实例变量)。

如何使用活动的私有共享Preference：

   1: protected void saveActivityPreference(){

   2:       // 创建或者检索活动的preference

   3:       SharedPreferences activityPreference = getPreferences(Activity.MODE_PRIVATE);

   4:       //找一个编辑器来修改共享的preference

   5:       SharedPreferences.Editor editor = activityPreference.edit();

6:

   7:       //检索View

   8:       TextView myTextView=(TextView)findViewById(R.id.myTextView);

9:

  10:       // 在共享的Preference对象中存储新的原语类型

  11:       editor.putString("currentTextValue", myTextVIew.getText().toString());

  12:       //提交修改

  13:       editor.commit();

  14:   }

⑴ 保存和恢复实例状态

重写onSaveInstanceState事件处理程序，用其参数Bundle参数来保存实例的值。使用相同的get和set方法对共享的preferenct的值进行存储，然后把修改过的Bundle传给超类的处理函数

   1: private static final String TEXTVIEW_STATIC_KEY = "TEXTVIEW_STATIC_KEY";

   2:   @Override

   3:   public void onSaveInstanceState(Bundle outState){

   4:       //检索View

   5:       TextView myTextVIew = (TextView)findViewById(R.id.myTextView);

   6:       //保存它的状态

   7:       outState.putString(TEXTVIEW_STATIC_KEY, myTextView.getText().toString());

   8:       super.onSaveInstanceState(outState);

   9:   }

onRestoreInstanceState在一次会话被强制重启时触发，Bundle会传递到其onCreate方法中。下列展示如何从Bundle中提取值，用它来更新活动的实例状态

   1: @Override

   2:   public void onCreate(Bundle icicle) {

   3:     super.onCreate(icicle);

   4:     setContentView(R.layout.preferences);

5:

   6:     TextView myTextVIew = (TextView)findViewById(R.id.myTextView);

7:

   8:     String text = "";

   9:     if(icicle != null && icicle.containsKey(TEXTVIEW_STATIC_KEY));

  10:     text = icicle.getString(TEXTVIEW_STATIC_KEY);

11:

  12:     myTextVIew.setText(text);

13:

  14:   }

⑵ 保存To-Do List活动状态

To-Do List（待办事项表）状态由三种变量组成：

·是否添加了新的条目

·新条目的输入文本框中存储了哪些文本？

·当前选择的条目是什么？

a.首先：添加静态字符串变量作为preference键

   1: // UI State Key Constants

   2:   static final private String TEXT_ENTRY_KEY = "TEXT_ENTRY_KEY";

   3:   static final private String ADDING_ITEM_KEY = "ADDING_ITEM_KEY";

   4:   static final private String SELECTED_INDEX_KEY = "SELECTED_INDEX_KEY";

b.重写onPause方法,取得私有共享preference的Editor对象

然后用第1步的键存储所列的实例值

   1: @Override

   2:   protected void onPause(){

   3:     super.onPause();

4:

   5:     // Get the activity preferences object.

   6:     SharedPreferences uiState = getPreferences(0);

   7:     // Get the preferences editor.

   8:     SharedPreferences.Editor editor = uiState.edit();

9:

  10:     // Add the UI state preference values.

  11:     editor.putString(TEXT_ENTRY_KEY, myEditText.getText().toString());

  12:     editor.putBoolean(ADDING_ITEM_KEY, addingNew);

13:

  14:     // Commit the preferences.

  15:     editor.commit();

  16:   }

⑶ 编写retoreUIState方法

   1: @Override

   2:   public void onCreate(Bundle icicle) {

   3:     super.onCreate(icicle);

   4:     ...

   5:     restoreUIState();

   6: }

7:

   8: /** Apply the saved UI state */

   9:   private void restoreUIState() {

  10:     // Get the activity preferences object.

  11:     SharedPreferences settings = getPreferences(0);

12:

  13:     // Read the UI state values, specifying default values.

  14:     String text = settings.getString(TEXT_ENTRY_KEY, "");

  15:     Boolean adding = settings.getBoolean(ADDING_ITEM_KEY, false);

16:

  17:     // Restore the UI to the previous state.

  18:     if (adding) {

  19:       addNewItem();

  20:       myEditText.setText(text);

  21:     }

  22:   }

⑷ 使用OnSaveInstanceState/onRestoreInstanceState记录选中条目的索引

   1: @Override

   2:   public void onSaveInstanceState(Bundle savedInstanceState) {

   3:     savedInstanceState.putInt(SELECTED_INDEX_KEY, myListView.getSelectedItemPosition());

4:

   5:     super.onSaveInstanceState(savedInstanceState);

   6:   }

7:

   8:   @Override

   9:   public void onRestoreInstanceState(Bundle savedInstanceState) {

  10:     int pos = -1;

11:

  12:     if (savedInstanceState != null)

  13:       if (savedInstanceState.containsKey(SELECTED_INDEX_KEY))

  14:         pos = savedInstanceState.getInt(SELECTED_INDEX_KEY, -1);

15:

  16:     myListView.setSelection(pos);

  17:   }

18:

4、为地震查看器创建一个preference页

(1)添加字符串资源，为显示的标签添加新的字符串资源

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="app_name">Earthquake</string>
  <string name="quake_feed">http://earthquake.usgs.gov/eqcenter/catalogs/1day-M2.5.xml</string>
  <string name="menu_update">Refresh Earthquakes</string>
  <string name="auto_update_prompt">Auto Update?</string>
  <string name="update_freq_prompt">Update Frequency</string>
  <string name="min_quake_mag_prompt">Minimum Quake Magnitude</string>
  <string name="menu_preferences">Preferences</string>
</resources>

(2)创建新的preferences.xml,布局preferences活动的UI

preferences.xml<LinearLayout 
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
  <TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/auto_update_prompt"
  />
  <CheckBox android:id="@+id/checkbox_auto_update"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"     
  />
  <TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/update_freq_prompt"
  />
  <Spinner android:id="@+id/spinner_update_freq"        
    android:layout_width="fill_parent"        
    android:layout_height="wrap_content"       
    android:drawSelectorOnTop="true"   
  />
  <TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/min_quake_mag_prompt"
  />
  <Spinner android:id="@+id/spinner_quake_mag"        
    android:layout_width="fill_parent"        
    android:layout_height="wrap_content"       
    android:drawSelectorOnTop="true"   
  />
  <LinearLayout
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content">
    <Button android:id="@+id/okButton"
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="@android:string/ok"
    />
    <Button android:id="@+id/cancelButton"
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="@android:string/cancel"
    />  
  </LinearLayout>
</LinearLayout>

(3)在res/values/arrays.xml文件中创建4个数组

arrays.xml<?xml version="1.0" encoding="utf-8"?>
<resources>
  <array name="update_freq_options">
    <item>Every Minute</item>
    <item>5 minutes</item>
    <item>10 minutes</item>
    <item>15 minutes</item>
    <item>Every Hour</item>
  </array>

  <array name="magnitude">
    <item>3</item>
    <item>5</item>
    <item>6</item>
    <item>7</item>
    <item>8</item>
  </array>
  
  <string-array name="magnitude_options">
    <item>3</item>
    <item>5</item>
    <item>6</item>
    <item>7</item>
    <item>8</item>
  </string-array>

  <array name="update_freq_values">
    <item>1</item>
    <item>5</item>
    <item>10</item>
    <item>15</item>
    <item>60</item>
  </array>
</resources>

(4) 创建preferenceit活动

重写onCreate,重写第2步的布局，获得复选框和spinner控件的引用，然后调用

populateSpinners存根

   1: public class Preferences extends Activity {

2:

   3:   CheckBox autoUpdate;

   4:   Spinner updateFreqSpinner;

   5:   Spinner magnitudeSpinner;

6:

   7: @Override

   8:   public void onCreate(Bundle icicle) {

   9:     super.onCreate(icicle);

  10:     setContentView(R.layout.preferences);

11:

  12:     updateFreqSpinner = (Spinner)findViewById(R.id.spinner_update_freq);

  13:     magnitudeSpinner = (Spinner)findViewById(R.id.spinner_quake_mag);

  14:     autoUpdate = (CheckBox)findViewById(R.id.checkbox_auto_update);

15:

  16:     populateSpinners();

  17:    }

18:

  19:     private void populateSpinners() {  }

  20: }

(5)用Array Adaper绑定spinner,完成populateSpinners():

   1: private void populateSpinners() {

   2:       // 填充更新频率

   3:       ArrayAdapter<CharSequence> fAdapter;

   4:       fAdapter = ArrayAdapter.createFromResource(this, R.array.update_freq_options,

   5:                                                  android.R.layout.simple_spinner_item);

   6:       fAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

   7:       updateFreqSpinner.setAdapter(fAdapter);

8:

   9:       // 填充最小震级

  10:          ArrayAdapter<CharSequence> mAdapter;

  11:          mAdapter = ArrayAdapter.createFromResource(this, R.array.magnitude_options,

  12:                                                     android.R.layout.simple_spinner_item);

  13:       mAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

  14:       magnitudeSpinner.setAdapter(mAdapter);

  15:     }

（6）创建命名的共享preference，更新onCreate进行检索preference，调用updateUIFromPreferences方法通过对共享的preference使用get<type>检索第一个preference值

   1: SharedPreferences prefs;

2:

   3:   public static final String USER_PREFERENCE = "USER_PREFERENCES";

4:

   5:   public static final String PREF_AUTO_UPDATE = "PREF_AUTO_UPDATE";

   6:   public static final String PREF_MIN_MAG = "PREF_MIN_MAG";

   7:   public static final String PREF_UPDATE_FREQ = "PREF_UPDATE_FREQ";

8:

   9:   @Override

  10:   public void onCreate(Bundle icicle) {

  11:     super.onCreate(icicle);

  12:     setContentView(R.layout.preferences);

13:

  14:     updateFreqSpinner = (Spinner)findViewById(R.id.spinner_update_freq);

  15:     magnitudeSpinner = (Spinner)findViewById(R.id.spinner_quake_mag);

  16:     autoUpdate = (CheckBox)findViewById(R.id.checkbox_auto_update);

17:

  18:     populateSpinners();

19:

  20:     prefs = getSharedPreferences(USER_PREFERENCE, Activity.MODE_PRIVATE);

  21:     updateUIFromPreferences();

  22:    }

   1: private void updateUIFromPreferences() {

   2:       boolean autoUpChecked = prefs.getBoolean(PREF_AUTO_UPDATE, false);

   3:       int updateFreqIndex = prefs.getInt(PREF_UPDATE_FREQ, 2);

   4:       int minMagIndex = prefs.getInt(PREF_MIN_MAG, 0);

5:

   6:       updateFreqSpinner.setSelection(updateFreqIndex);

   7:       magnitudeSpinner.setSelection(minMagIndex);

   8:       autoUpdate.setChecked(autoUpChecked);

   9:   }

(7)在onCreate方法中，添加OK和Cancel按钮的事件处理程序：OK按钮先调用savePreference,然后关闭活动

   1: @Override

   2:   public void onCreate(Bundle icicle) {

   3:     super.onCreate(icicle);

   4:     setContentView(R.layout.preferences);

5:

   6:     updateFreqSpinner = (Spinner)findViewById(R.id.spinner_update_freq);

   7:     magnitudeSpinner = (Spinner)findViewById(R.id.spinner_quake_mag);

   8:     autoUpdate = (CheckBox)findViewById(R.id.checkbox_auto_update);

9:

  10:         ....................

11:

  12:     Button okButton = (Button) findViewById(R.id.okButton);

  13:     okButton.setOnClickListener(new View.OnClickListener() {

  14:       public void onClick(View view) {

  15:         savePreferences();

  16:         Preferences.this.setResult(RESULT_OK);

  17:         finish();

  18:       }

  19:     });

20:

  21:     Button cancelButton = (Button) findViewById(R.id.cancelButton);

  22:     cancelButton.setOnClickListener(new View.OnClickListener() {

  23:       public void onClick(View view) {

  24:         Preferences.this.setResult(RESULT_CANCELED);

  25:         finish();

  26:       }

  27:     });

  28:   }

(8)根据UI选项记录当前的preference,存储到共享Preference

   1: private void savePreferences() {

   2:       int updateIndex = updateFreqSpinner.getSelectedItemPosition();

   3:       int minMagIndex = magnitudeSpinner.getSelectedItemPosition();

   4:       boolean autoUpdateChecked = autoUpdate.isChecked();

5:

   6:       Editor editor = prefs.edit();

   7:       editor.putBoolean(PREF_AUTO_UPDATE, autoUpdateChecked);

   8:       editor.putInt(PREF_UPDATE_FREQ, updateIndex);

   9:       editor.putInt(PREF_MIN_MAG, minMagIndex);

  10:       editor.commit();

  11:   }

(9) 将完成的preference活动添加到程序清单：

<activity android:name=".Preferences" android:label="Earthquake Preferences"></activity>

（10）在Earthquake活动中增加菜单项支持：重写onCreateOptionsMenu

   1: @Override

   2:   public boolean onCreateOptionsMenu(Menu menu) {

   3:     super.onCreateOptionsMenu(menu);

4:

   5:     menu.add(0, MENU_UPDATE, Menu.NONE, R.string.menu_update);

   6:     menu.add(0, MENU_PREFERENCES, Menu.NONE, R.string.menu_preferences);

7:

   8:     return true;

   9:   }

（11）修改onOptionsItemSelected，选择菜单项时，显示preference活动

创建一个Intert,传递给startActivityForResult,这将启动Preference屏幕，并通过onActivityResult处理程序保存Preference时通知Earthquake类

   1: @Override

   2:   public boolean onOptionsItemSelected(MenuItem item) {

   3:     super.onOptionsItemSelected(item);

4:

   5:     switch (item.getItemId()) {

   6:       case (MENU_UPDATE): {

   7:         refreshEarthquakes();

   8:         return true;

   9:       }

  10:       case (MENU_PREFERENCES): {

  11:         Intent i = new Intent(this, Preferences.class);

  12:         startActivityForResult(i, SHOW_PREFERENCES);

  13:         return true;

  14:       }

  15:     }

  16:     return false;

  17:   }

（12）启动程序，从菜单中选择Preference

（13）把Preference应用到Earthquake功能中,以上的应用框架已经搭好。

（14）创建updateFromPreferences读取共享Preference,为第一个值创建实例变量

   1: private void updateFromPreferences() {

   2:     SharedPreferences prefs = getSharedPreferences(Preferences.USER_PREFERENCE, Activity.MODE_PRIVATE);

3:

   4:     int minMagIndex = prefs.getInt(Preferences.PREF_MIN_MAG, 0);

   5:     if (minMagIndex < 0)

   6:       minMagIndex = 0;

7:

   8:     int freqIndex = prefs.getInt(Preferences.PREF_UPDATE_FREQ, 0);

   9:     if (freqIndex < 0)

  10:       freqIndex = 0;

11:

  12:     autoUpdate = prefs.getBoolean(Preferences.PREF_AUTO_UPDATE, false);

13:

  14:     Resources r = getResources();

  15:     // Get the option values from the arrays.

  16:     int[] minMagValues = r.getIntArray(R.array.magnitude);

  17:     int[] freqValues = r.getIntArray(R.array.update_freq_values);

18:

  19:     // Convert the values to ints.

  20:     minimumMagnitude = minMagValues[minMagIndex];

  21:     updateFreq = freqValues[freqIndex];

  22:   }

（15）更新addNewQuake方法，用地震过滤器来检查一个新的地震震级，然后将其添加到列表中

   1: private void addNewQuake(Quake _quake) {

   2:       if(_quake.getMagnitude()>minimumMagnitude)

   3:       //向我们的地震列表添加新的地震

   4:       earthquakes.add(_quake);

5:

   6:       // 把这个改变通知ArrayAdapter

   7:       aa.notifyDataSetChanged();

   8:     }

(16) 重写onActivityResult调用updateFormPreference,在保存了修改后刷新地震

   1: @Override

   2:   public void onActivityResult(int requestCode, int resultCode, Intent data) {

   3:     super.onActivityResult(requestCode, resultCode, data);

4:

   5:     if (requestCode == SHOW_PREFERENCES)

   6:       if (resultCode == Activity.RESULT_OK) {

   7:         updateFromPreferences();

   8:         refreshEarthquakes();

   9:       }

  10:   }

   1: @Override

   2:   public void onCreate(Bundle icicle) {

   3:     super.onCreate(icicle);

   4:     setContentView(R.layout.main);

5:

   6:     earthquakeListView = (ListView)this.findViewById(R.id.earthquakeListView);

   7:     earthquakeListView.setOnItemClickListener(new OnItemClickListener() {

   8:       public void onItemClick(AdapterView<?> _av, View _v, int _index, long _id) {

   9:         selectedQuake = earthquakes.get(_index);

  10:         showDialog(QUAKE_DIALOG);

  11:       }

  12:     });

13:

  14:     aa = new ArrayAdapter<Quake>(getApplicationContext(), android.R.layout.simple_list_item_1, earthquakes);

  15:     earthquakeListView.setAdapter(aa);

16:

  17:     loadQuakesFromProvider();

18:

  19:     updateFromPreferences();

  20:     refreshEarthquakes();

  21:   }

（17）在onCreate中调用updateFormPreference，在活动第一次启动时preference被应用

   1: @Override

   2:   public void onCreate(Bundle icicle) {

   3:     super.onCreate(icicle);

   4:     setContentView(R.layout.main);

5:

   6:     earthquakeListView = (ListView)this.findViewById(R.id.earthquakeListView);

   7:     earthquakeListView.setOnItemClickListener(new OnItemClickListener() {

   8:       public void onItemClick(AdapterView<?> _av, View _v, int _index, long _id) {

   9:         selectedQuake = earthquakes.get(_index);

  10:         showDialog(QUAKE_DIALOG);

  11:       }

  12:     });

13:

  14:     aa = new ArrayAdapter<Quake>(getApplicationContext(), android.R.layout.simple_list_item_1, earthquakes);

  15:     earthquakeListView.setAdapter(aa);

16:

  17:     loadQuakesFromProvider();

18:

  19:     updateFromPreferences();

  20:     refreshEarthquakes();

  21:   }

posted @ 2012-07-18 16:58 庙子阅读(395) 评论(0) 编辑收藏举报

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Android高级编程（笔记）-第6章数据存储、检索和共享--1--共享Preference

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Android高级编程（笔记）-第6章 数据存储、检索和共享--1--共享Preference

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Android高级编程（笔记）-第6章数据存储、检索和共享--1--共享Preference