如何检测用户何时滚动到ListView顶部并通过ListView传递触摸？

Question

在Android中，您如何检测用户何时已滚动到listView的顶部并在屏幕上向下拖动，即使他已到达ListView的顶部，然后将此触摸通过ListView进入父ViewGroup？

Answer 1

以下代码段将帮助您检测顶部过度滚动以及低于ListView的过度滚动，

listView.setOnTouchListener(new OnTouchListener() {

            private static final float OVERSCROLL_THRESHOLD_IN_PIXELS = 100;

            private float downY;

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                int firstVisibleItem = listView.getFirstVisiblePosition();
                int totalItemCount = listView.getCount();
                int visibleItemCount = listView.getChildCount();
                boolean onTop = firstVisibleItem == 0 && listView.getChildAt(0) != null && listView.getChildAt(0).getTop() == 0;
                boolean onBottom = firstVisibleItem + visibleItemCount == totalItemCount && listView.getChildAt(visibleItemCount-1).getBottom() == listView.getHeight();

                if(onTop || onBottom) {
                    switch(event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        downY = event.getY();
                        break;
                    case MotionEvent.ACTION_MOVE:
                        float deltaY = event.getY() - downY;
                        if(onTop && deltaY > OVERSCROLL_THRESHOLD_IN_PIXELS) 
                        {

                            // Top overscroll
                        }
                        if(onBottom && -deltaY > OVERSCROLL_THRESHOLD_IN_PIXELS) {
                            // Bottom overscroll
                        }
                        break;
                    }
                }

                return false;
            }
        });

Answer 2

重写方法onOverScrolled,以响应过度滚动操作的结果。在这种情况下，当用户到达顶部并滚动列表时，您需要事件。