android - 捏缩放自定义 View

Question

我已经创建了我的自定义 View ，我想为我的自定义 View 应用捏缩放。该怎么做？

Answer 1

Android 开发者博客上的这篇文章很好地涵盖了这个主题(向下滚动到 GestureDetectors 部分):

Making Sense of Multitouch

如果您只想实现捏合缩放，只需几行代码:

private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;

public MyCustomView(Context mContext){
    //...
    //Your view code
    //...
    mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    // Let the ScaleGestureDetector inspect all events.
    mScaleDetector.onTouchEvent(ev);
    return true;
}

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    canvas.save();
    canvas.scale(mScaleFactor, mScaleFactor);
    //...
    //Your onDraw() code
    //...
    canvas.restore();
}

private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        mScaleFactor *= detector.getScaleFactor();

        // Don't let the object get too small or too large.
        mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f));

        invalidate();
        return true;
    }
}

本文的其余部分涉及处理其他手势，但您可以使用 GestureDetector 而不是使用它们的实现就像上面代码中使用的ScaleGestureDetector一样。