Android 拖放自动滚动

Question

我正在尝试弄清楚当用户将项目拖动到屏幕边缘时如何自动滚动滚动视图。我真的没有从这段代码中得到我期望的行为。有没有人有有效的例子或技术？

我有这个：

onDrag(View v, DragEvent e)
{
   case DragAction.Location:

    var currentPosition = (int)e.GetX();

    var point = GetTouchPositionFromDragEvent(v, e);

    System.Diagnostics.Debug.WriteLine($"DragAction.Location from {v.GetType()} => {currentPosition}");
    System.Diagnostics.Debug.WriteLine($"DragAction.GLOBAL   from {v.GetType()} => {point.X}");

    if (point.X > App.AppScreenWidth - 50)
    {
        _hostScrollView.ScrollToAsync(_hostScrollView.ScrollX + 30, 0, true);
    }

    if (point.X < 50)
    {
        _hostScrollView.ScrollToAsync(_hostScrollView.ScrollX - 30, 0, true);
    }    
}

public static Point GetTouchPositionFromDragEvent(View item, DragEvent e) 
{
    Rect rItem = new Rect();
    item.GetGlobalVisibleRect(rItem);
    return new Point(rItem.Left + (int)Math.Round(e.GetX()), rItem.Top + (int)Math.Round(e.GetY()));
}

这也有一个连锁反应，奇怪的是只在一个方向滚动，还需要用户不断移动项目才能触发事件，这让我认为这是完全错误的地方，甚至尝试做这个滚动。

任何正确方向的指示或推动将不胜感激。

Answer 1

在你的Activity

public class MainActivity : AppCompatActivity, View.IOnDragListener,View.IOnScrollChangeListener

private int mScrollDistance;

 ScrollView _hostScrollView= FindViewById<ScrollView>(Resource.Id.xxx);
_hostScrollView.SetOnScrollChangeListener(this);

public bool OnDrag(View v, DragEvent e)
        {
            var action = e.Action;

            var scrollView = v as ScrollView;

            switch (action)
            {
                case DragAction.Started:

                    break;
                case DragAction.Location:
                    
                        int y = Java.Lang.Math.Round(e.GetY());
                        int translatedY = y - mScrollDistance;
                        int threshold = 50;
                        // make a scrolling up due the y has passed the threshold
                        if (translatedY < threshold)
                        {
                            // make a scroll up by 30 px
                            scrollView.ScrollBy(0, -30);
                        }
                        // make a autoscrolling down due y has passed the 500 px border
                        if (translatedY + threshold > 500)
                        {
                            // make a scroll down by 30 px
                            scrollView.ScrollBy(0, 30);
                        }
                   
                    break;
                    
            }
            return true;
        }

        public void OnScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY)
        {
            var scrollView = v as ScrollView;
            mScrollDistance = scrollView.ScrollY;
        }

如果我误解了你的要求，你可以根据需要修改逻辑。

Android 拖放自动滚动

Android Drag and DRop Auto Scroll

c#

drag-and-drop

xamarin

在你的Activity