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我正在尝试向 imageview 添加投掷手势。我正在使用此代码

public class MyActivity extends Activity {
private void onCreate() {
    final GestureDetector gdt = new GestureDetector(new GestureListener());
    final ImageView imageView  = (ImageView) findViewById(R.id.image_view);
    imageView.setOnTouchListener(new OnTouchListener() {
        @Override
        public boolean onTouch(final View view, final MotionEvent event) {
            gdt.onTouchEvent(event);
            return true;
        }
    });
}               

private static final int SWIPE_MIN_DISTANCE = 120;
private static final int SWIPE_THRESHOLD_VELOCITY = 200;

private class GestureListener extends SimpleOnGestureListener {
    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        if(e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
            return false; // Right to left
        }  else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
            return false; // Left to right
        }

        if(e1.getY() - e2.getY() > SWIPE_MIN_DISTANCE && Math.abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) {
            return false; // Bottom to top
        }  else if (e2.getY() - e1.getY() > SWIPE_MIN_DISTANCE && Math.abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) {
            return false; // Top to bottom
        }
        return false;
    }
}
}

但它只是行不通。日志说 nullpointerexception 它指的是这一行 imageView.setOnTouchListener(new OnTouchListener() {

我的错误在哪里？我错过了什么吗？

4

1 回答 1

1

你的 imageView 返回 null 因为你在实际获取 imageview 之前还没有 setContentView()

setContentView(R.layout.yourlayout)在你的 onCreate 获取 imageview 之前

于 2013-02-16T14:30:32.377 回答