在旋转的画布上绘制（设置暗区）

Question

我正在尝试创建一个将显示其子项已旋转的静态ViewGroup。它似乎工作得很好，除了整个画布没有重绘 - 似乎只有未旋转的孩子所覆盖的部分正在被重绘。

有没有办法在整个画布上强制绘图（比如将整个边框设置为脏）？

我的ViewGroup：

public class RotationGroup extends ViewGroup 
{
    private int rotation = 90;
    public RotationGroup(Context context, AttributeSet attrs)
    {
        super(context, attrs);
    }

    public RotationGroup(Context context) {
        super(context);
    }

    @Override
    protected void dispatchDraw(Canvas canvas)
    {
        canvas.save(Canvas.MATRIX_SAVE_FLAG);
        canvas.rotate(rotation, getWidth() * 0.5f, getHeight() * 0.5f);
        super.dispatchDraw(canvas);
        canvas.restore();
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {

        final int count = getChildCount();

        int maxHeight = 0;
        int maxWidth = 0;

        for (int i = 0; i < count; i++)
        {
            final View child = getChildAt(i);
            if( child!=null)
            {
                if( rotation==90 || rotation==-90)
                {
                    measureChild(child, heightMeasureSpec,widthMeasureSpec);
                    maxWidth = Math.max(maxWidth, child.getMeasuredHeight());
                    maxHeight = Math.max(maxHeight, child.getMeasuredWidth());
                }
                else
                {
                    measureChild(child, widthMeasureSpec, heightMeasureSpec);
                    maxWidth = Math.max(maxWidth, child.getMeasuredWidth());
                    maxHeight = Math.max(maxHeight, child.getMeasuredHeight());
                }
            }
        }
    }
    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom)
    {
        final int width = getWidth();
        final int height = getHeight();
        final int count = getChildCount();
        for (int i = 0; i < count; i++)
        {
            final View view = getChildAt(i);
            final int childWidth = view.getMeasuredWidth();
            final int childHeight = view.getMeasuredHeight();
            final int childLeft = (width - childWidth) / 2;
            final int childTop = (height - childHeight) / 2;
            view.layout(childLeft, childTop, childLeft + childWidth, childTop + childHeight);

        }
    }
}

示例布局：

<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
        <my.RotationGroup
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
        >
                <TextView 
                    android:text="Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem. Ut enim ad minima veniam, quis nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut aliquid ex ea commodi consequatur? Quis autem vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil molestiae consequatur, vel illum qui dolorem eum fugiat quo voluptas nulla pariatur?Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem. Ut enim ad minima veniam, quis nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut aliquid ex ea commodi consequatur? Quis autem vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil molestiae consequatur, vel illum qui dolorem eum fugiat quo voluptas nulla pariatur?"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                />

        </my.RotationGroup>
</LinearLayout>