zoom sur un canvas android

Bonsoir

j ai un probleme pour faire un zoom sur un canvas avec une erreur sur le onTouchEvent.
des que je clique sur l image l application crash et je ne sais comment gerer mon erreur .

Code:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
  private void drawBitmap(Canvas canvas) {
        canvas.save();
        canvas.translate(mPositionX,mPositionY);
        canvas.scale(mScaleFactor,mScaleFactor);
        canvas.drawBitmap(background,null,rect,null);
        canvas.drawBitmap(tank,(dWidht/2-tankWidth/2),dHeight-tankHeight,null);
        canvas.restore();
    }
    @Override
    public boolean onTouchEvent(MotionEvent event){
 
    mScaleDetector.onTouchEvent(event);
 
    switch (event.getAction()){
    case MotionEvent.ACTION_DOWN:
        refX =event.getX();
        refY=event.getY();
 
        paint((int)((refX-mPositionX)/mScaleFactor),(int)((refY-mPositionY)/mScaleFactor));
    break;
 
    case MotionEvent.ACTION_MOVE:
        float nX=event.getX();
        float nY=event.getY();
 
        mPositionX += nX-refX;
        mPositionY +=nY-refY;
        refX=nX;
        refY=nY;
        invalidate();
 
}
        return true;
    }
 
    private void paint(int x, int y) {
        if (x<0||x>=bitmap.getWidth()||y<0||y>=bitmap.getHeight())
   return;
    }
}

et ci joint l erreur

Code:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
2020-11-22 17:58:06.788 21138-21138/? E/InputEventReceiver: Exception dispatching input event.
2020-11-22 17:58:06.788 21138-21138/? E/MessageQueue-JNI: Exception in MessageQueue callback: 
handleReceiveCallback
2020-11-22 17:58:06.789 21138-21138/? E/MessageQueue-JNI: java.lang.NullPointerException: 
Attempt to invoke virtual method 'boolean 
android.view.ScaleGestureDetector.onTouchEvent(android.view.MotionEvent)' on a null object 
reference
    at com.example.myapplication.GameView.onTouchEvent(GameView.java:92)
    at android.view.View.dispatchTouchEvent(View.java:13551)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3088)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2724)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3088)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2724)
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3088)
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2724)
    at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:497)
    at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1853)
    at android.app.Activity.dispatchTouchEvent(Activity.java:4061)
    at com.android.internal.policy.DecorView.dispatchTouchEvent(DecorView.java:455)
    at android.view.View.dispatchPointerEvent(View.java:13812)
    at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:5649)
    at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:5449)
 
android

merci de votre aide