ScrollView的捏合缩放：当子视图大小改变时更新其滚动行为

Question

我有一个自定义类，它是从ScrollView扩展而来的。我想要做的是在这个类中实现捏合缩放功能，缩放到ScrollView的子级，并根据需要滚动缩放后的内容。基本上，我想要的行为与iOS的UIScrollView类相同（很遗憾Android没有像iOS那样提供内置缩放功能，我们必须从头开始编写所有内容）。我的类中有一个ScaleGestureListener，当我收到onScale事件时，我会更新ScrollView内部子视图的布局尺寸：用我从ScaleGestureListener接收到的比例因子乘以布局的宽度和高度。让我困扰的是，ScrollView不会根据其子级的新尺寸更新滚动条。例如，如果子级的宽度变大超过了ScrollView的宽度，它不会显示水平滚动条。我在滚动视图及其子级上都调用了invalidate和requestLayout，但它们都失败了。

以下是我的代码:

public class PinchZoomScrollView extends ScrollView{

private ScaleGestureDetector mScaleDetector;// = new ScaleGestureDetector(context, new ScaleListener());
private float mScaleFactor = 1.0f;
private float referenceTextSize;
private static final float MIN_ZOOM_AMOUNT = 1.0f;
private static final float MAX_ZOOM_AMOUNT = 2.0f;

private float refChildWidth;
private float refChildHeight;

private boolean shownForTheFirstTime = true;
//private View content;


private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {

    private WeakReference<PinchZoomScrollView> containerRef;

    public ScaleListener(PinchZoomScrollView container)
    {
        super();

        containerRef = new WeakReference<PinchZoomScrollView>(container);
    }

    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        mScaleFactor *= detector.getScaleFactor();

        // Don't let the object get too small or too large.
        mScaleFactor = Math.max(MIN_ZOOM_AMOUNT, Math.min(mScaleFactor, MAX_ZOOM_AMOUNT));

        //Get Child object
        View content = containerRef.get().getChildAt(0);

        if(shownForTheFirstTime)
        {
            shownForTheFirstTime = false;

            refChildWidth  = content.getWidth();
            refChildHeight = content.getHeight();
        }

        LayoutParams params = new LayoutParams(Math.round(mScaleFactor*refChildWidth), Math.round(mScaleFactor*refChildHeight));
        content.setLayoutParams(params);


        System.out.println("this.width="+containerRef.get().getWidth());
        System.out.println("content.width="+Math.round(mScaleFactor*refChildWidth));


        content.invalidate();
        content.requestLayout();

        containerRef.get().updateViewLayout(content, params);

        containerRef.get().invalidate();
        containerRef.get().requestLayout();

        return true;
    }
}


public PinchZoomScrollView(Context context)
{
    super(context);
    mScaleDetector = new ScaleGestureDetector(context, new ScaleListener(this));
}

public PinchZoomScrollView(Context context, AttributeSet attrs)
{
    super(context,attrs);
    mScaleDetector = new ScaleGestureDetector(context, new ScaleListener(this));
}

public PinchZoomScrollView(Context context, AttributeSet attrs, int defStyle)
{
    super(context,attrs,defStyle);
    mScaleDetector = new ScaleGestureDetector(context, new ScaleListener(this));
}

@Override
public boolean onTouchEvent(MotionEvent ev) {

    super.onTouchEvent(ev);

    mScaleDetector.onTouchEvent(ev);

    return true;
}

}

简而言之，每当用户进行缩放操作时，我需要ScrollView根据其子项的更新尺寸来更新滚动条。谢谢。

- Ufuk Can Bicici

Answer 1

这里是一个解决方案：

1. Rather than extending ScrollView, I wrote a TwoDimensionScrollView extending FrameLayout which is a combination of ScrollView and HorizontalScrollView so that it can show both horizontal/vertical scrollbars, even if the child is scaled. Also I did not use gesture detector. Instead, I implement my own pinch-to-zoom.

2. To update scroll bars, rewrite the functions below:

   @Override
   protected int computeVerticalScrollRange() {
       final int count = getChildCount();
       final int contentHeight = getHeight() - getPaddingBottom()
           - getPaddingTop();
       if (count == 0) {
           return contentHeight;
       }
   
   
   @Override
   protected int computeVerticalScrollOffset() {
       int result = Math.max(0, super.computeVerticalScrollOffset());
       return result - getScrollVerticalMin();
   }
   @Override
   protected int computeHorizontalScrollRange() {
       final int count = getChildCount();
       final int contentWidth = getWidth() - getPaddingLeft()
           - getPaddingRight();
       if (count == 0) {
           return contentWidth;
       }
   
       int scrollRange = getChildAt(0).getRight();
       final int scrollX = getScrollX();
       final int overscrollRight = Math.max(0, scrollRange - contentWidth);
       if (scrollX < 0) {
           scrollRange -= scrollX;
       } else if (scrollX > overscrollRight) {
           scrollRange += scrollX - overscrollRight;
       }
       return (int) (scrollRange * mScaleFactor + getScrollHorizontalMin());
   }
   
   @Override
   protected int computeHorizontalScrollOffset() {
       int result = Math.max(0, super.computeHorizontalScrollOffset());
       return result - getScrollHorizontalMin();
   }
   @Override
   protected int computeVerticalScrollExtent() {
       return getHeight() + getScrollVerticalMin();
   }
   
   @Override
   protected int computeHorizontalScrollExtent() {
       return getWidth() + getScrollHorizontalMin();
   }
   private int getScrollHorizontalMin() {
       if (this.getChildCount() < 1)
           return 0;
       View child = this.getChildAt(0);
       return (int) ((1 - mScaleFactor) * child.getPivotX());
   }
   
   private int getScrollVerticalMin() {
       if (this.getChildCount() < 1)
           return 0;
       View child = this.getChildAt(0);
       return (int) ((1 - mScaleFactor) * child.getPivotY());
   }
   private int getScrollVerticalRange() {
       int scrollRange = 0;
       if (getChildCount() > 0) {
           View child = getChildAt(0);
           scrollRange = (int) Math.max(0, child.getHeight() * mScaleFactor
                   - (getHeight() - getPaddingBottom() - getPaddingTop())
                   + getScrollVerticalMin());
       }
   return scrollRange;
   }
   
   private int getScrollHorizontalRange() {
       int scrollRange = 0;
       if (getChildCount() > 0) {
           View child = getChildAt(0);
           scrollRange = (int) Math.max(0, child.getWidth() * mScaleFactor
                   - (getWidth() - getPaddingRight() - getPaddingLeft())
                   + getScrollHorizontalMin());
       }
       return scrollRange;
   }
   

3. You also need to find all code calling SpringBack() and fling(), and then set the min value for x and y using the above functions getScrollHorizontalMin() and getScrollVerticalMin() instead of 0

- user2407188