Android:如何检测滚动何时结束 [英] Android: How to detect when a scroll has ended

问题描述

我正在使用 GestureDetector.SimpleOnGestureListener 的 onScroll 方法在画布上滚动大位图.当滚动结束时，我想重新绘制位图，以防用户想要进一步滚动......离开位图的边缘，但我无法看到如何检测滚动何时结束(用户抬起手指从屏幕上).

I am using the onScroll method of GestureDetector.SimpleOnGestureListener to scroll a large bitmap on a canvas. When the scroll has ended I want to redraw the bitmap in case the user wants to scroll further ... off the edge of the bitmap, but I can't see how to detect when the scroll has ended (the user has lifted his finger from the screen).

e2.getAction() 似乎总是返回值 2，因此没有帮助.e2.getPressure 似乎返回相当恒定的值(大约 0.25)，直到最后的 onScroll 调用时压力似乎下降到大约 0.13.我想我可以检测到这种压力的降低，但这远非万无一失.

e2.getAction() always seems to return the value 2 so that is no help. e2.getPressure seems to return fairly constant values (around 0.25) until the final onScroll call when the pressure seems to fall to about 0.13. I suppose I could detect this reduction in pressure, but this will be far from foolproof.

一定有更好的方法:有人可以帮忙吗?

There must be a better way: can anyone help, please?

推荐答案

这是我解决问题的方法.希望这会有所帮助.

Here is how I solved the problem. Hope this helps.

// declare class member variables
private GestureDetector mGestureDetector;
private OnTouchListener mGestureListener;
private boolean mIsScrolling = false;


public void initGestureDetection() {
        // Gesture detection
    mGestureDetector = new GestureDetector(new SimpleOnGestureListener() {
        @Override
        public boolean onDoubleTap(MotionEvent e) {
            handleDoubleTap(e);
            return true;
        }

        @Override
        public boolean onSingleTapConfirmed(MotionEvent e) {
            handleSingleTap(e);
            return true;
        }

        @Override
        public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
            // i'm only scrolling along the X axis
            mIsScrolling = true;                
            handleScroll(Math.round((e2.getX() - e1.getX())));
            return true;
        }

        @Override
        /**
         * Don't know why but we need to intercept this guy and return true so that the other gestures are handled.
         * https://code.google.com/p/android/issues/detail?id=8233
         */
        public boolean onDown(MotionEvent e) {
            Log.d("GestureDetector --> onDown");
            return true;
        }
    });

    mGestureListener = new View.OnTouchListener() {
        public boolean onTouch(View v, MotionEvent event) {

            if (mGestureDetector.onTouchEvent(event)) {
                return true;
            }

            if(event.getAction() == MotionEvent.ACTION_UP) {
                if(mIsScrolling ) {
                    Log.d("OnTouchListener --> onTouch ACTION_UP");
                    mIsScrolling  = false;
                    handleScrollFinished();
                };
            }

            return false;
        }
    };

    // attach the OnTouchListener to the image view
    mImageView.setOnTouchListener(mGestureListener);
}

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