使用Android中的拖放进行scrollView自动滚动

Question

我搜遍了所有,但找不到解决方案.

我在scrollview中有一个视图(让我们称之为myView).myView比屏幕大.由于我能够在myView中获取手指的相对 x,y位置,因此当我的手指进入某个上/下阈值时,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

好吧我自己弄清楚了.

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,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.

希望有所帮助.

Answer 2

我想出了一个不同的解决方案，对此我感到满意。

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

最后，我找到了一个解决方案，该解决方案可以检测到拖放区是否在滚动视图内部完全可见（边距为100像素），否则可以调整滚动视图。

@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！