竖着的Seekbar

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;        }    }  

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