android實現垂直seekbar

android系統自帶的拖動條（seekbar）只有橫向，這裡分享一個垂直的seekbar。

原理很簡單：

（1）在測量控件大小（包括發現控件大小改變時）時，把寬度和高度互換

（2）在繪制時將畫布順時針旋轉90度，即將拖動條逆時針旋轉90度，為了保證從畫布的原點開始繪制需要將畫布上移視圖高度

（3）自定義觸摸事件，根據觸摸的相對位置來修改progress變量的值。

代碼分享如下（這個代碼是很久以前網上找的，老外寫的）：

import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.ViewConfiguration;
import android.view.ViewParent;
import android.widget.SeekBar;

/**
 * 豎向拖動條
 */
public class VerticalSeekBar extends SeekBar {
    private boolean mIsDragging;
    private float mTouchDownY;
    private int mScaledTouchSlop;
    private boolean isInScrollingContainer = false;

    public boolean isInScrollingContainer() {
        return isInScrollingContainer;
    }

    public void setInScrollingContainer(boolean isInScrollingContainer) {
        this.isInScrollingContainer = isInScrollingContainer;
    }

    /**
     * On touch, this offset plus the scaled value from the position of the
	 *URL：http://www.bianceng.cn/OS/extra/201609/50429.htm
     * touch will form the progress value. Usually 0.
     */
    float mTouchProgressOffset;

    public VerticalSeekBar(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mScaledTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
    }

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

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

    @Override
    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());
    }

    @Override
    protected synchronized void onDraw(Canvas canvas) {
        canvas.rotate(90);
        canvas.translate(0, -getWidth());
        super.onDraw(canvas);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (!isEnabled()) {
            return false;
        }
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            if (isInScrollingContainer()) {
                mTouchDownY = event.getY();
            } else {
                setPressed(true);
                invalidate();
                onStartTrackingTouch();
                trackTouchEvent(event);
                attemptClaimDrag();
                onSizeChanged(getWidth(), getHeight(), 0, 0);
            }
            break;
        case MotionEvent.ACTION_MOVE:
            if (mIsDragging) {
                trackTouchEvent(event);
            } else {
                final float y = event.getY();
                if (Math.abs(y - mTouchDownY) > mScaledTouchSlop) {
                    setPressed(true);
                    invalidate();
                    onStartTrackingTouch();
                    trackTouchEvent(event);
                    attemptClaimDrag();
                }
            }
            onSizeChanged(getWidth(), getHeight(), 0, 0);
            break;
        case MotionEvent.ACTION_UP:
            if (mIsDragging) {
                trackTouchEvent(event);
                onStopTrackingTouch();
                setPressed(false);
            } else {
                // Touch up when we never crossed the touch slop threshold
                // should
                // be interpreted as a tap-seek to that location.
                onStartTrackingTouch();
                trackTouchEvent(event);
                onStopTrackingTouch();
            }
            onSizeChanged(getWidth(), getHeight(), 0, 0);
            // 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;
        }
        return true;
    }


    private void trackTouchEvent(MotionEvent event) {
        final int height = getHeight();
        final int top = getPaddingTop();
        final int bottom = getPaddingBottom();
        final int available = height - top - bottom;
        int y = (int) event.getY();
        float scale;
        float progress = 0;
        if (y > height - bottom) {
            scale = 0.0f;
        } else if (y < top) {
            scale = 1.0f;
        } else {
            scale = (float) (available - y + top) / (float) available;
            progress = mTouchProgressOffset;
        }
        final int max = getMax();
        // progress += scale * max;
        progress = Math.round(max * (1 - scale) - progress);
        setProgress((int) progress);
    }

    /**
     * This is called when the user has started touching this widget.
     */
    void onStartTrackingTouch() {
        mIsDragging = true;
    }

    /**
     * This is called when the user either releases his touch or the touch is
     * canceled.
     */
    void onStopTrackingTouch() {
        mIsDragging = false;
    }

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

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