android - 在 Android 中通过拖放创建一个 scrollView 自动滚动

Question

我到处搜索，但找不到解决方案。

我在滚动视图中有一个视图（我们称之为 myView）。myView 比屏幕大。由于我能够在 myView 中获得手指的相对x、y 位置，因此当我的手指进入某个顶部/底部阈值时，我想让 scrollView 自动滚动到顶部/底部。我有一些想法，即将拖动位置转换为屏幕位置，但这并没有解决这个问题。

提前致谢

干杯

Answer 1

好吧，我自己想通了。

首先我必须扩展 ScrollView 类并添加一个接口 OnScrollViewListener。

public class MyScrollView extends ScrollView {
    private OnScrollViewListener mListener;

    public MyScrollView(Context c, AttributeSet attrs) {
       super(c, attrs);
    }

    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
       super.onScrollChanged(l, t, oldl, oldt);
       if (mListener != null) {
           mListener.onScrollChanged((OnScrollViewListener) this);
       }
    }


    public void setOnScrollViewListener(OnScrollViewListener listener) {
       mListener = listener;
    }


    public static interface OnScrollViewListener {
       public void onScrollChanged(OnScrollViewListener listener);
    }
}

接下来在我的 Activity 中，我插入了一个成员 mScrollDistance，它指示用户滚动的像素数量。

public class ScrollActivity extends Activity {
   private int mScrollDistance;

   @Override
   protected void OnCreate(...) {
     ...

     final MyScrollView myScrollView = (MyScrollView) findViewById(R.id.scroll_view);
     myScrollView.setOnScrollViewListener(new MyScrollView.OnScrollViewListener() {

          public void onScrollChanged(OnScrollViewListener listener) {
             mScrollDistance = listener.getScrollY();
          }
     }

     // making an drag and drop in an view that is inside the MyScrollView
     final LinearLayout myLayout = (LinearLayout)findViewById(R.id.linear_layout);
     myLayout.setOnDragListener(new View.OnDragListener() {
       public boolean onDrag (View v, DragEvent event) {
         int action = event.getAction();
         switch(action) {
            case DragEvent.ACTION_DRAG_STARTED: {
            }
            case DragEvent.ACTION_DRAG_LOCATION: {

              int y = Math.round(event.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
                 myScrollView.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
                 myScrollView.scrollBy(0, 30);
              }
              // listen for more actions here
              // ...
            }
         }
       }
     }

现在，mScrollDistance 总是获得一个新值，并且拖动位置将被转换为视图位置。我对此进行了测试，它适用于大于屏幕尺寸的布局/视图。

希望有帮助。

Answer 2

我想出了一个不同的解决方案，我对此很满意。

我希望能够在 ScrollView 中拖放视图。当阴影到达滚动视图的边缘时，滚动视图需要自动上下滚动。

我最终得到了一个解决方案，该解决方案检测放置区域是否在滚动视图内完全可见（具有 100 像素的边距），否则调整滚动视图。

@Override
public boolean onDrag(View view, DragEvent event) {

    MainWidget dropZoneView = (MainWidget) view;

    int action = event.getAction();
    switch (action) {
        case DragEvent.ACTION_DRAG_STARTED:
        //(... other stuff happens here)
        case DragEvent.ACTION_DRAG_LOCATION:

            ScrollView mainScrollView = (ScrollView) findViewById(R.id.main_scroll);

            int topOfDropZone = dropZoneView.getTop();
            int bottomOfDropZone = dropZoneView.getBottom();

            int scrollY = mainScrollView.getScrollY();
            int scrollViewHeight = mainScrollView.getMeasuredHeight();

            Log.d(LOG_TAG,"location: Scroll Y: "+ scrollY + " Scroll Y+Height: "+(scrollY + scrollViewHeight));
            Log.d(LOG_TAG," top: "+ topOfDropZone +" bottom: "+bottomOfDropZone);

            if (bottomOfDropZone > (scrollY + scrollViewHeight - 100))
                mainScrollView.smoothScrollBy(0, 30);

            if (topOfDropZone < (scrollY + 100))
                mainScrollView.smoothScrollBy(0, -30);

            break;
        default:
            break;
    }
    return true;
}

希望这可以帮助！

Answer 3

我在 C# 中使用了一个计时器

ScrollCalendar ScrollCalendar = new ScrollCalendar (yourScrollView);

在拖动事件内部

    public bool OnDrag (View v, DragEvent e)
    {
        var dragshadow = new EventDateDragShadow (v);
        switch (e.Action) {
        case DragAction.Started:
            return true;
        case DragAction.Entered:
            break;
        case Android.Views.DragAction.Location:

            if (e.GetY () < 90) {
                ScrollCalendar.StartScroll (-15);
            } else if (e.GetY () > yourScrollView.Height - 90) {
                ScrollCalendar.StartScroll (15);
            } else
                ScrollCalendar.StopScroll ();

            return (true);
        case DragAction.Exited:
            return true;
        case DragAction.Drop:
            return true;
        case DragAction.Ended:
            ScrollCalendar.StopScroll ();
            v.SetOnDragListener (null);
            return true;
        }

        return true;
    }

ScrollCalendar 类

public class ScrollCalendar
{
    private ScrollView Calendar;
    private System.Timers.Timer Timer;
    private int ScrollDistance;

    public ScrollCalendar(ScrollView calendar)
    {
        Calendar = calendar;
        Timer = new System.Timers.Timer();
        Timer.Elapsed+=new ElapsedEventHandler(Scroll);
        Timer.Interval = 50;
    }

    public void StartScroll(int scrollDistance)
    {
        if (Timer.Enabled) {
            return;
        }
        ScrollDistance = scrollDistance;
        Timer.Enabled = true;
    }

    public void StopScroll()
    {
        Timer.Enabled = false;
    }

    private void Scroll(object source, ElapsedEventArgs e)
    {
        Calendar.SmoothScrollBy (0, ScrollDistance);
    }

}

更改 StartScroll 值和 Timer.Interval 以调整滚动速度。

Answer 4

我已经修改了 Tiago A 的答案。我遇到了同样的问题，Tiago A 的解决方案既小又简单，但有一些限制，所以如果其他人需要，这可能会有所帮助。感谢蒂亚戈 A。

case DragEvent.ACTION_DRAG_LOCATION:
                    ScrollView myScrollView =findViewById(R.id.myScrollView);
                    int topOfDropZone = myScrollView.getChildAt(0).getTop();
                    int bottomOfDropZone = myScrollView.getChildAt(0).getBottom();

                    int scrollY = myScrollView.getScrollY();
                    int scrollViewHeight = myScrollView.getMeasuredHeight();

                    if (Math.round(event.getY()) > scrollViewHeight - (scrollViewHeight / 45))
                        if (bottomOfDropZone > (scrollY + scrollViewHeight - 100))
                            myScrollView.smoothScrollBy(0, 30);

                    if (Math.round(event.getY()) < (scrollViewHeight / 45))
                        if (topOfDropZone < (scrollY + 100))
                            myScrollView.smoothScrollBy(0, -30);

                    return true;