拖动时移动图像

Question

我想要移动一张图片。我这样做是为了在onTouch事件中移动图像

        float downx = 0;
float downy = 0;
float upx = 0;
float upy = 0;

public boolean onTouch(View v, MotionEvent event) { 
    int action = event.getAction();
    switch (action) {
    case MotionEvent.ACTION_DOWN:
        downx = event.getX();
        downy = event.getY();
        break;
    case MotionEvent.ACTION_MOVE:
        upx = event.getX();
        upy = event.getY();


        CompositeImageViewText.invalidate();
                canvas.drawBitmap(bmw, upx,upy, paint);
         CompositeImageViewText.setImageBitmap(bmw);
        downx = upx;
        downy = upy;
        break;
    case MotionEvent.ACTION_UP:
        upx = event.getX();
        upy = event.getY(); 
        break;
    case MotionEvent.ACTION_CANCEL:
        break; 
    default:
        break; 
    }

    return true;
}

但是我经历了这样做的力量。可能是什么问题？我的代码是否正确？

logcat粘贴在

下面

01-05 02:08:30.995: E/AndroidRuntime(1240):     at com.apress.proandroidmedia.ch3.choosepicturecomposite.ChoosePictureComposite.onTouch(ChoosePictureComposite.java:335)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.view.View.dispatchTouchEvent(View.java:3881)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1691)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1125)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.app.Activity.dispatchTouchEvent(Activity.java:2096)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1675)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.view.ViewRoot.deliverPointerEvent(ViewRoot.java:2194)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1878)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.os.Looper.loop(Looper.java:130)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at android.app.ActivityThread.main(ActivityThread.java:3683)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at java.lang.reflect.Method.invokeNative(Native Method)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at java.lang.reflect.Method.invoke(Method.java:507)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-05 02:08:30.995: E/AndroidRuntime(1240):     at dalvik.system.NativeStart.main(Native Method)