Android：檢測觸摸事件崩潰

Question

我正在爲我的應用程序實現觸摸事件時崩潰。我想爲我的應用程序實施滑動功能。請看看的代碼之後，

GueturesImplementation：

package com.example.EventsView; 

import android.app.Activity; 
import android.view.GestureDetector; 
import android.view.GestureDetector.SimpleOnGestureListener; 
import android.view.MotionEvent; 

public class GuesterFilter extends SimpleOnGestureListener{ 

public final static int SWIPE_UP = 1; 
public final static int SWIPE_DOWN = 2; 
public final static int SWIPE_LEFT = 3; 
public final static int SWIPE_RIGHT = 4; 

public final static int MODE_TRANSPARENT = 0; 
public final static int MODE_SOLID  = 1; 
public final static int MODE_DYNAMIC  = 2; 

private final static int ACTION_FAKE = -13; //just an unlikely number 
private int swipe_Min_Distance = 100; 
private int swipe_Max_Distance = 350; 
private int swipe_Min_Velocity = 100; 

private int mode  = MODE_DYNAMIC; 
private boolean running = true; 
private boolean tapIndicator = false; 

private Activity context; 
private GestureDetector detector; 
private SimpleGestureListener listener; 


public GuesterFilter(Activity context,SimpleGestureListener sgl) { 

this.context = context; 
this.detector = new GestureDetector(context, this); 
this.listener = sgl; 
} 

public void onTouchEvent(MotionEvent event){ 

    if(!this.running) 
return; 

    boolean result = this.detector.onTouchEvent(event); 

    if(this.mode == MODE_SOLID) 
event.setAction(MotionEvent.ACTION_CANCEL); 
    else if (this.mode == MODE_DYNAMIC) { 

if(event.getAction() == ACTION_FAKE) 
    event.setAction(MotionEvent.ACTION_UP); 
    else if (result) 
    event.setAction(MotionEvent.ACTION_CANCEL); 
else if(this.tapIndicator){ 
    event.setAction(MotionEvent.ACTION_DOWN); 
    this.tapIndicator = false; 
} 

    } 
      //else just do nothing, it's Transparent 
    } 

    public void setMode(int m){ 
     this.mode = m; 
    } 

    public int getMode(){ 
     return this.mode; 
    } 

    public void setEnabled(boolean status){ 
     this.running = status; 
    } 

    public void setSwipeMaxDistance(int distance){ 
    this.swipe_Max_Distance = distance; 
    } 

    public void setSwipeMinDistance(int distance){ 
    this.swipe_Min_Distance = distance; 
    } 

    public void setSwipeMinVelocity(int distance){ 
    this.swipe_Min_Velocity = distance; 
    } 

    public int getSwipeMaxDistance(){ 
    return this.swipe_Max_Distance; 
    } 

    public int getSwipeMinDistance(){ 
    return this.swipe_Min_Distance; 
    } 

    public int getSwipeMinVelocity(){ 
     return this.swipe_Min_Velocity; 
    } 


    @Override 
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, 
    float velocityY) { 

    final float xDistance = Math.abs(e1.getX() - e2.getX()); 
    final float yDistance = Math.abs(e1.getY() - e2.getY()); 

    if(xDistance > this.swipe_Max_Distance || yDistance > this.swipe_Max_Distance) 
    return false; 

    velocityX = Math.abs(velocityX); 
     velocityY = Math.abs(velocityY); 
     boolean result = false; 

    if(velocityX > this.swipe_Min_Velocity && xDistance > this.swipe_Min_Distance){ 
    if(e1.getX() > e2.getX()) // right to left 
    this.listener.onSwipe(SWIPE_LEFT); 
    else 
    this.listener.onSwipe(SWIPE_RIGHT); 

    result = true; 
    } 
    else if(velocityY > this.swipe_Min_Velocity && yDistance > this.swipe_Min_Distance){ 
    if(e1.getY() > e2.getY()) // bottom to up 
    this.listener.onSwipe(SWIPE_UP); 
    else 
    this.listener.onSwipe(SWIPE_DOWN); 

    result = true; 
    } 

    return result; 
    } 

     @Override 
     public boolean onSingleTapUp(MotionEvent e) { 
     this.tapIndicator = true; 
     return false; 
     } 

     @Override 
     public boolean onDoubleTap(MotionEvent arg0) { 
     this.listener.onDoubleTap();; 
     return true; 
     } 

     @Override 
     public boolean onDoubleTapEvent(MotionEvent arg0) { 
     return true; 
     } 

     @Override 
    public boolean onSingleTapConfirmed(MotionEvent arg0) { 

    if(this.mode == MODE_DYNAMIC){  // we owe an ACTION_UP, so we fake an  
     arg0.setAction(ACTION_FAKE);  //action which will be converted to an ACTION_UP  later.          
     this.context.dispatchTouchEvent(arg0); 
    } 

    return false; 
    } 


    static interface SimpleGestureListener{ 
     void onSwipe(int direction); 
     void onDoubleTap(); 
    } 

} 

觀活動實施：

package com.example.EventsView; 

import android.app.Activity; 
import android.os.Bundle; 
import android.view.MotionEvent; 
import android.view.Window; 
import android.view.WindowManager; 
import android.widget.Toast; 

import com.example.mobilefit.GuesterFilter.SimpleGestureListener; 

public class BeginYourWorkout extends Activity implements SimpleGestureListener 
{ 
    private GuesterFilter detector; 
    protected void onCreate(Bundle savedInstanceState) 
    { 
     requestWindowFeature(Window.FEATURE_NO_TITLE); 
      getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
           WindowManager.LayoutParams.FLAG_FULLSCREEN); 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.eventsView); 
    } 

    public boolean dispatchTouchEvent(MotionEvent me) 

    { 
     this.detector.onTouchEvent(me); 
     return super.dispatchTouchEvent(me); 


    } 

    @Override 
public void onSwipe(int direction) 
{ 
     String str = ""; 

     switch (direction) { 

     case GuesterFilter.SWIPE_RIGHT : str = "Swipe Right"; 
               break; 
     case GuesterFilter.SWIPE_LEFT : str = "Swipe Left"; 
                break; 
     case GuesterFilter.SWIPE_DOWN : str = "Swipe Down"; 
                break; 
     case GuesterFilter.SWIPE_UP : str = "Swipe Up"; 
                break; 

     } 
     Toast.makeText(this, str, Toast.LENGTH_SHORT).show(); 
    } 
@Override 
public void onDoubleTap() 
{ 
    Toast.makeText(this, "Double Tap", Toast.LENGTH_SHORT).show(); 
} 
public boolean onSingleTapUp(MotionEvent e) 
{ 
    Toast.makeText(this, "Double Tap", Toast.LENGTH_SHORT).show(); 
     return false; 
} 

}

錯誤登錄：

FATAL EXCEPTION: main 
java.lang.NullPointerException 
at com.example.myPackage.EventsView.dispatchTouchEvent(EventsView.java:27) 
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1901) 
at android.view.View.dispatchPointerEvent(View.java:7419) 
at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3220) 
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3165) 
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4292) 
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4271) 
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4363) 
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:179) 
at android.os.MessageQueue.nativePollOnce(Native Method) 
at android.os.MessageQueue.next(MessageQueue.java:125) 
at android.os.Looper.loop(Looper.java:124) 
at android.app.ActivityThread.main(ActivityThread.java:5039) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
at dalvik.system.NativeStart.main(Native Method) 

Answer 1

public GuesterFilter(Activity context,SimpleGestureListener sgl)可能永遠不會被調用。

必須至少調用它才能初始化this.context。

試試這個代碼：

public class BeginYourWorkout extends Activity implements SimpleGestureListener 
{ 
    private GuesterFilter detector; 
    protected void onCreate(Bundle savedInstanceState) 
    { 
     requestWindowFeature(Window.FEATURE_NO_TITLE); 
      getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
           WindowManager.LayoutParams.FLAG_FULLSCREEN); 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.eventsView); 

     this.detector = new GuesterFilter(this, this); 
    } 

    //... 
} 

Answer 2

你永遠不會用新的實例化探測器。