android-数据持久化

浏览数：21 / 时间：2015年06月11日

动态文件

String FILE_NAME = "tempfile.tmp";
                try {
                    
                    //读
                    FileInputStream fis = openFileInput(FILE_NAME);
                    InputStreamReader isr = new InputStreamReader(fis, "UTF-8");
                    BufferedReader br = new BufferedReader(isr);
                    StringBuffer sb = new StringBuffer();
                    while (br.readLine() != null) {
                        sb.append(br.readLine()+"\n");
                    }
                    System.out.println(sb.toString());
                    
                    //写
                    FileOutputStream fos = openFileOutput(FILE_NAME, Context.MODE_PRIVATE);//要让其它应用组件也能访问则用MODE_WORLD_WRITEABLE
                    File file = new File(FILE_NAME);
                    if (!file.exists()) {
                        byte[] os = "write file".getBytes("UTF-8");//"这个例子测试文件写".getBytes("GB2312");
                        fos.write(os);
                    }
                    
                } catch (FileNotFoundException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (UnsupportedEncodingException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

静态文件资源

//这个id是在gen的R.java中生成id. 项目层次结构为res/raw里
                    InputStream is = getResources().openRawResource(R.raw.info);
                    InputStreamReader isr;
                    isr = new InputStreamReader(is, "UTF-8");
                    BufferedReader bfr = new BufferedReader(isr);
                    String inString = "";
                    while ((inString = bfr.readLine()) != null) {
                        Log.i(TAG, inString);
                    }

首选项

int minimumMagnitude = 0;
boolean autoUpdate = false;
int updateFreq = 0;

//读
Context context = getApplicationContext();
      SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);

      minimumMagnitude = Integer.parseInt(prefs.getString(Preferences.PREF_MIN_MAG, "0"));
      updateFreq = Integer.parseInt(prefs.getString(Preferences.PREF_UPDATE_FREQ, "0"));
      autoUpdate = prefs.getBoolean(Preferences.PREF_AUTO_UPDATE, false);


//写
Context context = getApplicationContext();
    prefs = PreferenceManager.getDefaultSharedPreferences(context);
Editor editor = prefs.edit();
    editor.putBoolean(PREF_AUTO_UPDATE, autoUpdateChecked);
    editor.putInt(PREF_UPDATE_FREQ, updateIndex);
    editor.putInt(PREF_MIN_MAG, minMagIndex);
    editor.commit();

Preferences界面是继承PreferencesActivity，则只需要：

@res/xml/userpreferences.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen
  xmlns:android="http://schemas.android.com/apk/res/android">
  <CheckBoxPreference
    android:key="PREF_AUTO_UPDATE"
    android:title="Auto refresh"
    android:summary="Select to turn on automatic updating" 
    android:defaultValue="true"
  />                        
  <ListPreference
   android:key="PREF_UPDATE_FREQ"
   android:title="Refresh frequency"
   android:summary="Frequency at which to refresh earthquake list"
   android:entries="@array/update_freq_options"
   android:entryValues="@array/update_freq_values"
   android:dialogTitle="Refresh frequency"
   android:defaultValue="60"
  />
  <ListPreference
    android:key="PREF_MIN_MAG"
    android:title="Minimum magnitude"
    android:summary="Select the minimum magnitude earthquake to report"
    android:entries="@array/magnitude_options"
    android:entryValues="@array/magnitude"
    android:dialogTitle="Magnitude"
    android:defaultValue="3"
  />
</PreferenceScreen>


@PreferencesActivity

public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    addPreferencesFromResource(R.xml.userpreferences);    
  }

否则，需要在Preferences中手动设置控件的状态值，包括ok和cancel键所执行的动作回调。

监听preference的改变

@Activity

public void onCreate(Bundle icicle) {
    Context context = getApplicationContext();
    SharedPreferences prefs =  PreferenceManager.getDefaultSharedPreferences(context);
    prefs.registerOnSharedPreferenceChangeListener(this);   
  } 

public void onSharedPreferenceChanged(SharedPreferences prefs, String key) {
}

从activity的preference中读写

private ListView myListView;
private EditText myEditText;
private static final String TEXT_ENTRY_KEY = "TEXT_ENTRY_KEY";
private static final String ADDING_ITEM_KEY = "ADDING_ITEM_KEY";

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Inflate your view
    setContentView(R.layout.main);
      
    // Get references to UI widgets
    myListView = (ListView)findViewById(R.id.myListView);
    myEditText = (EditText)findViewById(R.id.myEditText);

    restoreUIState();
  }

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);
    }
  }

@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();
  }

状态

private static final String SELECTED_INDEX_KEY = "SELECTED_INDEX_KEY";

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

    super.onSaveInstanceState(outState);
  }

  @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);
  }