Android overrided methods never calls

• Z时代
• 2024-01-10
• 分类：问答

这是Activity类的示例代码，我尝试通过调用实现OnListGestureDetectorTest接口的setOnListGestureDetectorTest方法（下面的第二个示例代码）覆盖ListGestureDetector类的方法。进行彻底的调试，我意识到覆盖函数onRTLFling，onLTRFling和customOnItemClick从来没有调用过。只有从ListGestureDetector类中调用原始的空函数。我做错了什么，以及为什么overriden函数永远不会调用？Android overrided methods never calls

ListGestureDetector listGestureDetectorListener = new ListGestureDetector(
      this, mEarningsListView); 
    listGestureDetectorListener 
      .setOnListGestureDetectorTest(new ListGestureDetector.OnListGestureDetectorTest() { 
       @Override 
       public void onRTLFling(int pos) { 
        Log.d(TAG,"onRTLFling"); 
       } 
       @Override 
       public void onLTRFling(int pos) { 
        Log.d(TAG,"onLTRFling"); 
       } 
       @Override 
       public void customOnItemClick(int position) { 
        Log.d(TAG,"onLTRFling"); 
       } 
      }); 
    final GestureDetector gestureDetector = new GestureDetector(
      listGestureDetectorListener); 
    View.OnTouchListener gestureListener = new View.OnTouchListener() { 
     public boolean onTouch(View v, MotionEvent event) { 
      return gestureDetector.onTouchEvent(event); 
     } 
    }; 
    mEarningsListView.setOnTouchListener(gestureListener); 

这是ListGestureDetector类

public class ListGestureDetector extends SimpleOnGestureListener { 
private int REL_SWIPE_MIN_DISTANCE; 
private int REL_SWIPE_MAX_OFF_PATH; 
private int REL_SWIPE_THRESHOLD_VELOCITY; 
private ListView mList; 
// Detect a single-click and call my own handler. 
@Override 
public boolean onSingleTapUp(MotionEvent e) { 
    int pos = mList.pointToPosition((int) e.getX(), (int) e.getY()); 
    customOnItemClick(pos); 
    return false; 
} 
@Override 
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, 
     float velocityY) { 
    if (Math.abs(e1.getY() - e2.getY()) > REL_SWIPE_MAX_OFF_PATH) 
     return false; 
    if (e1.getX() - e2.getX() > REL_SWIPE_MIN_DISTANCE 
      && Math.abs(velocityX) > REL_SWIPE_THRESHOLD_VELOCITY) { 
     int pos = mList.pointToPosition((int) e1.getX(), 
       (int) e1.getY()); 
     onRTLFling(pos); 
    } else if (e2.getX() - e1.getX() > REL_SWIPE_MIN_DISTANCE 
      && Math.abs(velocityX) > REL_SWIPE_THRESHOLD_VELOCITY) { 
     int pos = mList.pointToPosition((int) e1.getX(), 
       (int) e1.getY()); 
     onLTRFling(pos); 
    } 
    return false; 
} 
public ListGestureDetector(Context c, ListView list) { 
    super(); 
    mList = list; 
    // Density-aware measurements 
    DisplayMetrics dm = c.getResources().getDisplayMetrics(); 
    REL_SWIPE_MIN_DISTANCE = (int) (120.0f * dm.densityDpi/160.0f + 0.5); 
    REL_SWIPE_MAX_OFF_PATH = (int) (250.0f * dm.densityDpi/160.0f + 0.5); 
    REL_SWIPE_THRESHOLD_VELOCITY = (int) (200.0f * dm.densityDpi/160.0f + 0.5); 
} 
interface OnListGestureDetectorTest { 
    void customOnItemClick(int position); 
    void onRTLFling(int pos); 
    void onLTRFling(int pos); 
} 
public void customOnItemClick(int position) { 
} 
public void onRTLFling(int pos) {  
} 
public void onLTRFling(int pos) {  
} 
public void setOnListGestureDetectorTest(OnListGestureDetectorTest ogd) {  
} 
} 

回答：

public class ListGestureDetector extends SimpleOnGestureListener { 
private int REL_SWIPE_MIN_DISTANCE; 
private int REL_SWIPE_MAX_OFF_PATH; 
private int REL_SWIPE_THRESHOLD_VELOCITY; 
private ListView mList; 
OnListGestureDetector onListGestureDetector = null; 
// Detect a single-click and call my own handler. 
@Override 
public boolean onSingleTapUp(MotionEvent e) { 
    int pos = mList.pointToPosition((int) e.getX(), (int) e.getY()); 
    onListGestureDetector.customOnItemClick(pos); 
    return false; 
} 
@Override 
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, 
     float velocityY) { 
    if (Math.abs(e1.getY() - e2.getY()) > REL_SWIPE_MAX_OFF_PATH) 
     return false; 
    if (e1.getX() - e2.getX() > REL_SWIPE_MIN_DISTANCE 
      && Math.abs(velocityX) > REL_SWIPE_THRESHOLD_VELOCITY) { 
     int pos = mList.pointToPosition((int) e1.getX(), 
       (int) e1.getY()); 
     onListGestureDetector.onRTLFling(pos); 
    } else if (e2.getX() - e1.getX() > REL_SWIPE_MIN_DISTANCE 
      && Math.abs(velocityX) > REL_SWIPE_THRESHOLD_VELOCITY) { 
     int pos = mList.pointToPosition((int) e1.getX(), 
       (int) e1.getY()); 
     onListGestureDetector.onLTRFling(pos); 
    } 
    return false; 
} 
public ListGestureDetector(Context c, ListView list) { 
    super(); 
    mList = list; 
    // Density-aware measurements 
    DisplayMetrics dm = c.getResources().getDisplayMetrics(); 
    REL_SWIPE_MIN_DISTANCE = (int) (120.0f * dm.densityDpi/160.0f + 0.5); 
    REL_SWIPE_MAX_OFF_PATH = (int) (250.0f * dm.densityDpi/160.0f + 0.5); 
    REL_SWIPE_THRESHOLD_VELOCITY = (int) (200.0f * dm.densityDpi/160.0f + 0.5); 
} 
interface OnListGestureDetector { 
    public abstract void customOnItemClick(int position); 
    public abstract void onRTLFling(int pos); 
    public abstract void onLTRFling(int pos); 
} 
public void setOnListGestureDetector(OnListGestureDetector ogd) { 
    onListGestureDetector = ogd; 
} 
} 

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