GestorDetector在片段不能正常工作

Question

我對Android開發非常陌生我試圖將一個活動轉換爲一個片段，除了作爲我經歷的老教程之外，它在活動中運行良好。我已經找出了一些錯誤，並且我確信有更多的東西需要整理，因此歡迎任何額外的提示。

這裏是代碼，我的日誌也在下面。我只是在我的MainActivity中使用navigationView來啓動這個片段。

categorySelectFragment.java

public class categorySelectorFragment extends Fragment { 

private ViewFlipper mViewFlipper; 
private int mSpeed; 
private int mCount; 
private int mFactor; 
private boolean mAnimating; 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 

    View view = inflater.inflate(R.layout.category_selector, container, false); 

    mViewFlipper = (ViewFlipper)getActivity().findViewById(R.id.view_flipper); 
    //mDetector = new GestureDetector(getActivity(), this); 
    mAnimating = false; 
    mCount = 0; 
    mSpeed = 0; 

    final GestureDetector gesture = new GestureDetector(getActivity(), new GestureDetector.SimpleOnGestureListener() { 

     @Override 
     public boolean onDown(MotionEvent e) { 
      // TODO Auto-generated method stub 
      return true; 
     } 

     private Runnable r1 = new Runnable() { 

      @Override 
      public void run() { 
       up(); 
       if (mCount<1) { 
        mAnimating = false; 
       } else { 
        Handler h = new Handler(); 
        h.postDelayed(r1, mSpeed); 
       } 
      } 

     }; 

     private Runnable r2 = new Runnable() { 

      @Override 
      public void run() { 
       down(); 
       if (mCount<1) { 
        mAnimating = false; 
       } else { 
        Handler h = new Handler(); 
        h.postDelayed(r2, mSpeed); 
       } 
      } 

     }; 

     @Override 
     public boolean onFling(MotionEvent start, MotionEvent finish, float xVelocity, float yVelocity) { 
      try { 
       if (mAnimating) return true; 
       mAnimating = true; 
       mCount = (int) Math.abs(yVelocity)/300; 
       mFactor = (int) 300/mCount; 
       mSpeed = mFactor; 
       if (yVelocity>0) { 
        //down 
        Handler h = new Handler(); 
        h.postDelayed(r2, mSpeed); 
       } else { 
        //up 
        Handler h = new Handler(); 
        h.postDelayed(r1, mSpeed); 
       } 
       ((TextView)getActivity().findViewById(R.id.velocity)).setText("VELOCITY => "+Float.toString(yVelocity)); 
      } catch (ArithmeticException e) { 
       //swiped too slow doesn't register 
       mAnimating = false; 
      } 
      return true; 
     } 

     private void up() { 
      mCount--; 
      mSpeed+=mFactor; 
      Animation inFromBottom = new TranslateAnimation(
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, 1.0f, 
        Animation.RELATIVE_TO_PARENT, 0.0f); 
      inFromBottom.setInterpolator(new AccelerateInterpolator()); 
      inFromBottom.setDuration(mSpeed); 
      Animation outToTop = new TranslateAnimation(
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, -1.0f); 
      outToTop.setInterpolator(new AccelerateInterpolator()); 
      outToTop.setDuration(mSpeed); 
      mViewFlipper.clearAnimation(); 
      mViewFlipper.setInAnimation(inFromBottom); 
      mViewFlipper.setOutAnimation(outToTop); 
      if (mViewFlipper.getDisplayedChild()==0) { 
       mViewFlipper.setDisplayedChild(2); 
      } else { 
       mViewFlipper.showPrevious(); 
      } 
      ((TextView)getActivity().findViewById(R.id.counter)).setText("COUNTER => "+Integer.toString(mCount)); 
      ((TextView)getActivity().findViewById(R.id.speed)).setText("SPEED => "+Integer.toString(mSpeed)); 
     } 

     private void down() { 
      mCount--; 
      mSpeed+=mFactor; 
      Animation outToBottom = new TranslateAnimation(
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, 1.0f); 
      outToBottom.setInterpolator(new AccelerateInterpolator()); 
      outToBottom.setDuration(mSpeed); 
      Animation inFromTop = new TranslateAnimation(
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, 0.0f, 
        Animation.RELATIVE_TO_PARENT, -1.0f, 
        Animation.RELATIVE_TO_PARENT, 0.0f); 
      inFromTop.setInterpolator(new AccelerateInterpolator()); 
      inFromTop.setDuration(mSpeed); 
      mViewFlipper.clearAnimation(); 
      mViewFlipper.setInAnimation(inFromTop); 
      mViewFlipper.setOutAnimation(outToBottom); 
      if (mViewFlipper.getDisplayedChild()==0) { 
       mViewFlipper.setDisplayedChild(2); 
      } else { 
       mViewFlipper.showPrevious(); 
      } 
      ((TextView)getActivity().findViewById(R.id.counter)).setText("COUNTER => "+Integer.toString(mCount)); 
      ((TextView)getActivity().findViewById(R.id.speed)).setText("SPEED => "+Integer.toString(mSpeed)); 
     } 

     @Override 
     public void onLongPress(MotionEvent e) { 
      // TODO Auto-generated method stub 

     } 

     @Override 
     public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) { 
      // TODO Auto-generated method stub 
      return false; 
     } 

     @Override 
     public void onShowPress(MotionEvent e) { 
      // TODO Auto-generated method stub 

     } 

     @Override 
     public boolean onSingleTapUp(MotionEvent e) { 
      // TODO Auto-generated method stub 
      return false; 
     } 

     public void onSwipeRight() { 
      Toast.makeText(getActivity(), " RIGHT ", Toast.LENGTH_LONG).show(); 
     } 

     public void onSwipeLeft() { 
      Toast.makeText(getActivity(), " LEFT ", Toast.LENGTH_LONG).show(); 


     } 

     public void onSwipeTop() { 
      Toast.makeText(getActivity(), " TOP ", Toast.LENGTH_LONG).show(); 

     } 

     public void onSwipeBottom() { 
      Toast.makeText(getActivity(), " BOTTOM ", Toast.LENGTH_LONG).show(); 

     } 


    }); 


    view.setOnTouchListener(new View.OnTouchListener() { 
     @Override 
     public boolean onTouch(View v, MotionEvent event) { 
      return gesture.onTouchEvent(event); 
     } 
    }); 

    return view; 


} 

}

logcat的

FATAL EXCEPTION: main 
Process: com.example.game, PID: 9403 

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ViewFlipper.clearAnimation()' on a null object reference 

at com.example.game.categorySelectorFragment$1.up(categorySelectorFragment.java:122) 
at com.example.game.categorySelectorFragment$1.access$000(categorySelectorFragment.java:42) 
at com.example.game.categorySelectorFragment$1$1.run(categorySelectorFragment.java:54) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:158) 
at android.app.ActivityThread.main(ActivityThread.java:7229) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 

感謝您的幫助！

Answer 1

1）嘗試替換 mViewFlipper =（ViewFlipper）getActivity（）。findViewById（R.id.view_flipper）; 與 mViewFlipper =（ViewFlipper）view.findViewById（R.id.view_flipper）;

2）我建議你在onActivityCreated（）方法中初始化視圖。