Android Seekbar竖直

视频播放器页面音量控制Seekbar实现竖直的效果。竖直只是将Seekbar转了90度或-90度，我们可以把画布转一个角度，然后交给系统去画，
具体的做法就是重写ondraw()调整画布，然后调用super.onDraw()。

• 向上的Seekbar

    protected void onDraw(Canvas c) {
        c.rotate(-90);
        c.translate(-height,0);//height是你的verticalseekbar的高
        super.onDraw(c);
    }

• 向下的seekbar则应该是：

    protected void onDraw(Canvas c) {
        c.rotate(90);
        c.translate(0,-width);//width是你的verticalseekbar的宽
        super.onDraw(c);
    }

• 示例代码

    public class VerticalSeekBar extends SeekBar {
        public VerticalSeekBar(Context context) {
            super(context);
        }
        public VerticalSeekBar(Context context, AttributeSet attrs, int defStyle) {
            super(context, attrs, defStyle);
        }
        public VerticalSeekBar(Context context, AttributeSet attrs) {
            super(context, attrs);
        }
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(h, w, oldh, oldw);
        }

        @Override
        protected synchronized void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            super.onMeasure(heightMeasureSpec, widthMeasureSpec);
            setMeasuredDimension(getMeasuredHeight(), getMeasuredWidth());
        }

        protected void onDraw(Canvas c) {
            c.rotate(-90);
            c.translate(-getHeight(), 0);
            super.onDraw(c);
        }

        @Override
        public synchronized void setProgress(int progress) {
            super.setProgress(progress);
            onSizeChanged(getWidth(), getHeight(), 0, 0);  
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            if (!isEnabled()) {
                return false;
            }
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                case MotionEvent.ACTION_MOVE:
                case MotionEvent.ACTION_UP:
                    setProgress((int) ((int) getMax()- (getMax() * event.getY() / getHeight())));
                    break;
                default:
                    return super.onTouchEvent(event);
            }
            return true;
        }
    }