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：

protected void saveActivityPreference(){
      // 创建或者检索活动的preference
      SharedPreferences activityPreference = getPreferences(Activity.MODE_PRIVATE);
      //找一个编辑器来修改共享的preference
      SharedPreferences.Editor editor = activityPreference.edit();

      //检索View
      TextView myTextView=(TextView)findViewById(R.id.myTextView);

      // 在共享的Preference对象中存储新的原语类型
      editor.putString("currentTextValue", myTextVIew.getText().toString());
      //提交修改
      editor.commit();
  }

    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

private static final String TEXTVIEW_STATIC_KEY = "TEXTVIEW_STATIC_KEY";
  @Override
  public void onSaveInstanceState(Bundle outState){
      //检索View
      TextView myTextVIew = (TextView)findViewById(R.id.myTextView);
      //保存它的状态
      outState.putString(TEXTVIEW_STATIC_KEY, myTextView.getText().toString());
      super.onSaveInstanceState(outState);
  }

        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

@Override
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.preferences);

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

    String text = "";
    if(icicle != null && icicle.containsKey(TEXTVIEW_STATIC_KEY));
    text = icicle.getString(TEXTVIEW_STATIC_KEY);

    myTextVIew.setText(text);

  }

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

// UI State Key Constants
  static final private String TEXT_ENTRY_KEY = "TEXT_ENTRY_KEY";
  static final private String ADDING_ITEM_KEY = "ADDING_ITEM_KEY";
  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

@Override
  protected void onPause(){
    super.onPause();

    // Get the activity preferences object.
    SharedPreferences uiState = getPreferences(0);
    // Get the preferences editor.
    SharedPreferences.Editor editor = uiState.edit();

    // Add the UI state preference values.
    editor.putString(TEXT_ENTRY_KEY, myEditText.getText().toString());
    editor.putBoolean(ADDING_ITEM_KEY, addingNew);

    // Commit the preferences.
    editor.commit();
  }

⑶ 编写retoreUIState方法

@Override
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    ...
    restoreUIState();
}

/** Apply the saved UI state */
  private void restoreUIState() {
    // Get the activity preferences object.
    SharedPreferences settings = getPreferences(0);

    // Read the UI state values, specifying default values.
    String text = settings.getString(TEXT_ENTRY_KEY, "");
    Boolean adding = settings.getBoolean(ADDING_ITEM_KEY, false);

    // Restore the UI to the previous state.
    if (adding) {
      addNewItem();
      myEditText.setText(text);
    }
  }

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

@Override
  public void onSaveInstanceState(Bundle savedInstanceState) {
    savedInstanceState.putInt(SELECTED_INDEX_KEY, myListView.getSelectedItemPosition());

    super.onSaveInstanceState(savedInstanceState);
  }

  @Override
  public void onRestoreInstanceState(Bundle savedInstanceState) {
    int pos = -1;

    if (savedInstanceState != null)
      if (savedInstanceState.containsKey(SELECTED_INDEX_KEY))
        pos = savedInstanceState.getInt(SELECTED_INDEX_KEY, -1);

    myListView.setSelection(pos);
  }

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

<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

<?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

public class Preferences extends Activity {

  CheckBox autoUpdate;
  Spinner updateFreqSpinner;
  Spinner magnitudeSpinner;

@Override
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.preferences);

    updateFreqSpinner = (Spinner)findViewById(R.id.spinner_update_freq);
    magnitudeSpinner = (Spinner)findViewById(R.id.spinner_quake_mag);
    autoUpdate = (CheckBox)findViewById(R.id.checkbox_auto_update);

    populateSpinners();
   }

    private void populateSpinners() {  }
}

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

 

private void populateSpinners() {
      // 填充更新频率
      ArrayAdapter<CharSequence> fAdapter;
      fAdapter = ArrayAdapter.createFromResource(this, R.array.update_freq_options,
                                                 android.R.layout.simple_spinner_item);
      fAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
      updateFreqSpinner.setAdapter(fAdapter);

      // 填充最小震级
         ArrayAdapter<CharSequence> mAdapter;
         mAdapter = ArrayAdapter.createFromResource(this, R.array.magnitude_options,
                                                    android.R.layout.simple_spinner_item);
      mAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
      magnitudeSpinner.setAdapter(mAdapter);
    }

（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

SharedPreferences prefs;

  public static final String USER_PREFERENCE = "USER_PREFERENCES";

  public static final String PREF_AUTO_UPDATE = "PREF_AUTO_UPDATE";
  public static final String PREF_MIN_MAG = "PREF_MIN_MAG";
  public static final String PREF_UPDATE_FREQ = "PREF_UPDATE_FREQ";

  @Override
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.preferences);

    updateFreqSpinner = (Spinner)findViewById(R.id.spinner_update_freq);
    magnitudeSpinner = (Spinner)findViewById(R.id.spinner_quake_mag);
    autoUpdate = (CheckBox)findViewById(R.id.checkbox_auto_update);

    populateSpinners();

    prefs = getSharedPreferences(USER_PREFERENCE, Activity.MODE_PRIVATE);
    updateUIFromPreferences();
   }

private void updateUIFromPreferences() {
      boolean autoUpChecked = prefs.getBoolean(PREF_AUTO_UPDATE, false);
      int updateFreqIndex = prefs.getInt(PREF_UPDATE_FREQ, 2);
      int minMagIndex = prefs.getInt(PREF_MIN_MAG, 0);

      updateFreqSpinner.setSelection(updateFreqIndex);
      magnitudeSpinner.setSelection(minMagIndex);
      autoUpdate.setChecked(autoUpChecked);
  }

(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

@Override
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.preferences);

    updateFreqSpinner = (Spinner)findViewById(R.id.spinner_update_freq);
    magnitudeSpinner = (Spinner)findViewById(R.id.spinner_quake_mag);
    autoUpdate = (CheckBox)findViewById(R.id.checkbox_auto_update);

        ....................

    Button okButton = (Button) findViewById(R.id.okButton);
    okButton.setOnClickListener(new View.OnClickListener() {
      public void onClick(View view) {
        savePreferences();
        Preferences.this.setResult(RESULT_OK);
        finish();
      }
    });

    Button cancelButton = (Button) findViewById(R.id.cancelButton);
    cancelButton.setOnClickListener(new View.OnClickListener() {
      public void onClick(View view) {
        Preferences.this.setResult(RESULT_CANCELED);
        finish();
      }
    });
  }

 

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

 

private void savePreferences() {
      int updateIndex = updateFreqSpinner.getSelectedItemPosition();
      int minMagIndex = magnitudeSpinner.getSelectedItemPosition();
      boolean autoUpdateChecked = autoUpdate.isChecked();

      Editor editor = prefs.edit();
      editor.putBoolean(PREF_AUTO_UPDATE, autoUpdateChecked);
      editor.putInt(PREF_UPDATE_FREQ, updateIndex);
      editor.putInt(PREF_MIN_MAG, minMagIndex);
      editor.commit();
  }

(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

@Override
  public boolean onCreateOptionsMenu(Menu menu) {
    super.onCreateOptionsMenu(menu);

    menu.add(0, MENU_UPDATE, Menu.NONE, R.string.menu_update);
    menu.add(0, MENU_PREFERENCES, Menu.NONE, R.string.menu_preferences);

    return true;
  }

（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

@Override
  public boolean onOptionsItemSelected(MenuItem item) {
    super.onOptionsItemSelected(item);

    switch (item.getItemId()) {
      case (MENU_UPDATE): {
        refreshEarthquakes();
        return true;
      }
      case (MENU_PREFERENCES): {
        Intent i = new Intent(this, Preferences.class);
        startActivityForResult(i, SHOW_PREFERENCES);
        return true;
      }
    }
    return false;
  }

 

（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

private void updateFromPreferences() {
    SharedPreferences prefs = getSharedPreferences(Preferences.USER_PREFERENCE, Activity.MODE_PRIVATE);

    int minMagIndex = prefs.getInt(Preferences.PREF_MIN_MAG, 0);
    if (minMagIndex < 0)
      minMagIndex = 0;

    int freqIndex = prefs.getInt(Preferences.PREF_UPDATE_FREQ, 0);
    if (freqIndex < 0)
      freqIndex = 0;

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

    Resources r = getResources();
    // Get the option values from the arrays.
    int[] minMagValues = r.getIntArray(R.array.magnitude);
    int[] freqValues = r.getIntArray(R.array.update_freq_values);

    // Convert the values to ints.
    minimumMagnitude = minMagValues[minMagIndex];
    updateFreq = freqValues[freqIndex];
  }

（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

private void addNewQuake(Quake _quake) {
      if(_quake.getMagnitude()>minimumMagnitude)
      //向我们的地震列表添加新的地震
      earthquakes.add(_quake);

      // 把这个改变通知ArrayAdapter
      aa.notifyDataSetChanged();
    }

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

@Override
  public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == SHOW_PREFERENCES)
      if (resultCode == Activity.RESULT_OK) {
        updateFromPreferences();
        refreshEarthquakes();
      }
  }

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

@Override
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.main);

    earthquakeListView = (ListView)this.findViewById(R.id.earthquakeListView);
    earthquakeListView.setOnItemClickListener(new OnItemClickListener() {
      public void onItemClick(AdapterView<?> _av, View _v, int _index, long _id) {
        selectedQuake = earthquakes.get(_index);
        showDialog(QUAKE_DIALOG);
      }
    });

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

    loadQuakesFromProvider();

    updateFromPreferences();
    refreshEarthquakes();
  }

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

@Override
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.main);

    earthquakeListView = (ListView)this.findViewById(R.id.earthquakeListView);
    earthquakeListView.setOnItemClickListener(new OnItemClickListener() {
      public void onItemClick(AdapterView<?> _av, View _v, int _index, long _id) {
        selectedQuake = earthquakes.get(_index);
        showDialog(QUAKE_DIALOG);
      }
    });

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

    loadQuakesFromProvider();

    updateFromPreferences();
    refreshEarthquakes();
  }