public class VerticalSeekBar extends AbsSeekBar {

    private Drawable mThumb;

    public interface OnSeekBarChangeListener {
        void onProgressChanged(VerticalSeekBar VerticalSeekBar, int progress, boolean fromUser);

        void onStartTrackingTouch(VerticalSeekBar VerticalSeekBar);

        void onStopTrackingTouch(VerticalSeekBar VerticalSeekBar);
    }

    private OnSeekBarChangeListener mOnSeekBarChangeListener;

    public VerticalSeekBar(Context context) {
        this(context, null);
    }

    public VerticalSeekBar(Context context, AttributeSet attrs) {
        this(context, attrs, android.R.attr.seekBarStyle);
    }

    public VerticalSeekBar(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public void setOnSeekBarChangeListener(OnSeekBarChangeListener l) {
        mOnSeekBarChangeListener = l;
    }

    void onStartTrackingTouch() {
        if (mOnSeekBarChangeListener != null) {
            mOnSeekBarChangeListener.onStartTrackingTouch(this);
        }
    }

    void onStopTrackingTouch() {
        if (mOnSeekBarChangeListener != null) {
            mOnSeekBarChangeListener.onStopTrackingTouch(this);
        }
    }

    void onProgressRefresh(float scale, boolean fromUser) {
        Drawable thumb = mThumb;
        if (thumb != null) {
            setThumbPos(getHeight(), thumb, scale, Integer.MIN_VALUE);
            invalidate();
        }
        if (mOnSeekBarChangeListener != null) {
            mOnSeekBarChangeListener.onProgressChanged(this, getProgress(), isPressed());
        }
    }

    private void setThumbPos(int w, Drawable thumb, float scale, int gap) {
        int available = w - getPaddingLeft() - getPaddingRight();
        int thumbWidth = thumb.getIntrinsicWidth();
        int thumbHeight = thumb.getIntrinsicHeight();
        available -= thumbWidth;

        // The extra space for the thumb to move on the track
        available += getThumbOffset() * 2;

        int thumbPos = (int) (scale * available);

        int topBound, bottomBound;
        if (gap == Integer.MIN_VALUE) {
            Rect oldBounds = thumb.getBounds();
            topBound = oldBounds.top;
            bottomBound = oldBounds.bottom;
        } else {
            topBound = gap;
            bottomBound = gap + thumbHeight;
        }
        thumb.setBounds(thumbPos, topBound, thumbPos + thumbWidth, bottomBound);
    }

    @Override
    protected void onDraw(Canvas c) {
        c.rotate(-90);// 反转90度，将水平SeekBar竖起来
        c.translate(-getHeight(), 0);// 将经过旋转后得到的VerticalSeekBar移到正确的位置,注意经旋转后宽高值互换
        super.onDraw(c);
    }

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

    @Override
    public void setThumb(Drawable thumb) {
        mThumb = thumb;
        super.setThumb(thumb);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(h, w, oldw, oldh);// 宽高值互换
    }

    // 与源码完全相同，仅为调用宽高值互换处理的onStartTrackingTouch()方法
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (!isEnabled()) {
            return false;
        }
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN: {
            setPressed(true);
            onStartTrackingTouch();
            trackTouchEvent(event);
            break;
        }

        case MotionEvent.ACTION_MOVE: {
            trackTouchEvent(event);
            attemptClaimDrag();
            break;
        }

        case MotionEvent.ACTION_UP: {
            trackTouchEvent(event);
            onStopTrackingTouch();
            setPressed(false);
            // ProgressBar doesn't know to repaint the thumb drawable
            // in its inactive state when the touch stops (because the
            // value has not apparently changed)
            invalidate();
            break;
        }

        case MotionEvent.ACTION_CANCEL: {
            onStopTrackingTouch();
            setPressed(false);
            invalidate(); // see above explanation
            break;
        }

        default:
            break;
        }
        return true;
    }

    // 宽高值互换处理
    private void trackTouchEvent(MotionEvent event) {
        final int height = getHeight();
        final int available = height - getPaddingBottom() - getPaddingTop();
        int Y = (int) event.getY();
        float scale;
        float progress = 0;
        if (Y > height - getPaddingBottom()) {
            scale = 0.0f;
        } else if (Y < getPaddingTop()) {
            scale = 1.0f;
        } else {
            scale = (float) (height - getPaddingBottom() - Y) / (float) available;
        }
        final int max = getMax();
        progress = scale * max;
        setProgress((int) progress);
    }

    private void attemptClaimDrag() {
        if (getParent() != null) {
            getParent().requestDisallowInterceptTouchEvent(true);
        }
    }
}