如何通過Android中的反射來實例化偵聽器

Question

我必須爲Android 1.6（API 4）開發一個應用程序，該應用程序應該能夠在Android 2.2或更高版本的Android 2.2手機中使用OnAudioFocusChangeListener（可用於Android 2.2 - API 8）後來。

任何人都可以告訴我如何通過反射實例化偵聽器？ 我已經設法通過反射運行靜態和非靜態方法，但我不知道如何處理偵聽器。

這是聽衆反映：

AudioManager audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE); 

OnAudioFocusChangeListener audioListener = new OnAudioFocusChangeListener() { 
    @Override 
    public void onAudioFocusChange(int focusChange) { 
    // code to execute 
    } 
}; 

public void getAudioFocus() { 
    audioManager.requestAudioFocus(audioListener, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN); 
} 

public void releaseAudioFocus() { 
    audioManager.abandonAudioFocus(audioListener); 
} 

這是一個有方法的代碼示例，我設法通過反射來運行：

Class BluetoothAdapter = Class.forName("android.bluetooth.BluetoothAdapter"); 
Method methodGetDefaultAdapter = BluetoothAdapter.getMethod("getDefaultAdapter"); // static method from the BluetoothAdapter class returning a BluetoothAdapter object 
Object bluetooth = methodGetDefaultAdapter.invoke(null); 
Method methodGetState = bluetooth.getClass().getMethod("getState"); // non-static method executed from the BluetoothAdapter object (which I called "bluetooth") returning an int 
int bluetoothState = (Integer) methodGetState.invoke(bluetooth); 

Answer 1

最後我通過使用Proxy類來解決它。這是代碼！

private AudioManager theAudioManager; 
private Object myOnAudioFocusChangeListener = null; 

private static final int AUDIOMANAGER_AUDIOFOCUS_GAIN = 1; 
private static final int AUDIOMANAGER_AUDIOFOCUS_LOSS = -1; 

theAudioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE); 

// instantiating the OnAudioFocusChangeListener by reflection (as it only exists from Android 2.2 onwards) 
// we use a Proxy class for implementing the listener 
public void setOnAudioFocusChangeListener() { 
    Log.i(this, "setOnAudioFocusChangeListener()"); 
    Class<?>[] innerClasses = theAudioManager.getClass().getDeclaredClasses(); 
    for (Class<?> interfaze : innerClasses) { 
     if (interfaze.getSimpleName().equalsIgnoreCase("OnAudioFocusChangeListener")) { 
      Class<?>[] classArray = new Class<?>[1]; 
      classArray[0] = interfaze; 
      myOnAudioFocusChangeListener = Proxy.newProxyInstance(interfaze.getClassLoader(), classArray, new ProxyOnAudioFocusChangeListener()); 
     } 
    } 
} 

// called by onResume 
public void getAudioFocus() { 
    if (myOnAudioFocusChangeListener != null) { 
     Log.i(this, "getAudioFocus()"); 
     try { 
      Method[] methods = theAudioManager.getClass().getDeclaredMethods(); 
      for (Method method : methods) { 
       if (method.getName().equalsIgnoreCase("requestAudioFocus")) { 
        method.invoke(theAudioManager, myOnAudioFocusChangeListener, AudioManager.STREAM_MUSIC, AUDIOMANAGER_AUDIOFOCUS_GAIN); 
        Log.i(this, "requestAudioFocus"); 
       } 
      } 
     } catch (Exception e) { 
      Log.e(this, e.getMessage()); 
     } 
    } 
} 

// called by onPause 
public void releaseAudioFocus() { 
    if (myOnAudioFocusChangeListener != null) { 
     Log.i(this, "releaseAudioFocus()"); 
     try { 
      Method[] methods = theAudioManager.getClass().getDeclaredMethods(); 
      for (Method method : methods) { 
       if (method.getName().equalsIgnoreCase("abandonAudioFocus")) 
        method.invoke(theAudioManager, myOnAudioFocusChangeListener); 
      } 
     } catch (Exception e) { 
      Log.e(this, e.getMessage()); 
     } 
    } 
} 

PROXY OnAudioFocusChangeListener類

private class ProxyOnAudioFocusChangeListener implements InvocationHandler { 

    // implements the method onAudioFocusChange from the OnAudioFocusChangeListener 
    public void onAudioFocusChange(int focusChange) { 
     Log.e(this, "onAudioFocusChange() focusChange = " + focusChange); 
     if (focusChange == AUDIOMANAGER_AUDIOFOCUS_LOSS) { 
      Log.i(this, "AUDIOMANAGER_AUDIOFOCUS_LOSS"); 
      Message msg = mHandler.obtainMessage(ControllerHandler.SET_ON_PAUSE); 
      mHandler.sendMessage(msg); 
     } else if (focusChange == AUDIOMANAGER_AUDIOFOCUS_GAIN) { 
      Log.i(this, "AUDIOMANAGER_AUDIOFOCUS_GAIN"); 
      // no action is taken 
     } 
    } 

    // implements the method invoke from the InvocationHandler interface 
    // it intercepts the calls to the listener methods 
    // in this case it redirects the onAudioFocusChange listener method to the OnAudioFocusChange proxy method 
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { 
     Object result = null; 
     try { 
      if (args != null) { 
       if (method.getName().equals("onAudioFocusChange") && args[0] instanceof Integer) { 
        onAudioFocusChange((Integer) args[0]); 
       } 
      } 
     } catch (Exception e) { 
      throw new RuntimeException("unexpected invocation exception: " + e.getMessage()); 
     } 
     return result; 
    } 
} 

Answer 2

恕我直言反射會使你的類的可讀性。反射速度也比正常的場地或課程訪問慢很多。

作爲替代看到這裏所描述的包裝類方法：http://android-developers.blogspot.com/2009/04/backward-compatibility-for-android.html

創建界面和它的兩個實現，一個用於API 8+和其他的早期版本。在您的API8類中，您可以使用API​​ 8類，包括OnAudioFocusChangeListener。然後基於OS版本實例化版本，您可以通過Build.VERSION.SDK_INT進行檢查。