Android技术分享| 自定义View实现使用更方便的SeekBar

Posted 2022-02-07 anyRTC

前言

android中自带的SeekBar个人感觉用起来很麻烦，调整一些颜色之类的需要单独写一个XML文件，内容感觉也很啰嗦。刚好我们的白板Demo开发中需要用到SeekBar，所以干脆实现了一个满足基本功能的SeekBar，支持在xml布局中指定各种颜色属性，也支持代码动态设置颜色。用起来更顺心一些。

SeekBar的代码请查看Github地址：白板Demo，Demo地址请：点击这里
即拿即用，非常方便;p（记得将res/values/styles.xml中的属性一并复制走）

效果

实现

由于不涉及到动画，这种自定义View做起来还是相当简单的。首先在res/values/styles.xml文件中定义好自己需要的属性，我这里贴上我定义的属性：

<declare-styleable name="SeekBarWidget">
    <attr name="seek_maxProgress" format="integer" /><!-- 最大progress -->
    <attr name="seek_minProgress" format="integer" /><!-- 最小progress -->
    <attr name="seek_progress" format="integer" /><!-- 当前progress(默认值) -->
    <attr name="seek_circleRadius" format="dimension" /><!-- seekBar中间圆形的半径 -->
    <attr name="seek_circleStrokeWidth" format="dimension" /><!-- seekBar中间圆形外的border -->
    <attr name="seek_lineHeight" format="dimension" /><!-- lineHeight有点词不达意，其实是进度条的高度 -->
    <attr name="seek_backgroundColor" format="color" /><!-- 进度条的背景色 -->
    <attr name="seek_circleStrokeColor" format="color" /><!-- border的颜色 -->
    <attr name="seek_maxColor" format="color" /><!-- 进度条的前景色 -->
    <attr name="seek_startColor" format="color" /><!-- 如果需要渐变色则设置此属性，否则这条属性置空即可 -->
</declare-styleable>

属性定义好以后，在View的构造中解析一下：

public SeekBarWidget(Context context) 
    this(context, null);

                                                                                                                           
public SeekBarWidget(Context context, @Nullable AttributeSet attrs) 
    this(context, attrs, 0);

                                                                                                                           
public SeekBarWidget(Context context, @Nullable AttributeSet attrs, int defStyleAttr) 
    super(context, attrs, defStyleAttr);
                                                                                                                          
    if (null != attrs) 
        TypedArray typedArray = getResources().obtainAttributes(attrs, R.styleable.SeekBarWidget);
        minProgress = typedArray.getInt(R.styleable.SeekBarWidget_seek_minProgress, 0);
        maxProgress = typedArray.getInt(R.styleable.SeekBarWidget_seek_maxProgress, 100) - minProgress;
        progress = typedArray.getInt(R.styleable.SeekBarWidget_seek_progress, 0) - minProgress;
        if (progress < 0) progress = minProgress;
        circleRadius = typedArray.getDimension(R.styleable.SeekBarWidget_seek_circleRadius, 20f);
        circleStrokeWidth = typedArray.getDimension(R.styleable.SeekBarWidget_seek_circleStrokeWidth, 5f);
        lineHeight = typedArray.getDimension(R.styleable.SeekBarWidget_seek_lineHeight, 5f);
        backgroundColor = typedArray.getColor(R.styleable.SeekBarWidget_seek_backgroundColor, Color.parseColor("#F0F0F0"));
        circleStrokeColor = typedArray.getColor(R.styleable.SeekBarWidget_seek_circleStrokeColor, Color.WHITE);
        int maxColor = typedArray.getColor(R.styleable.SeekBarWidget_seek_maxColor, Color.RED);
        int startColor = typedArray.getColor(R.styleable.SeekBarWidget_seek_startColor, maxColor);
        colorTransition = new ColorTransition(startColor, maxColor);
        typedArray.recycle();
        percentage = progress * 1.0f / maxProgress;
        horizontalPadding = circleRadius * 2 + circleStrokeWidth * 2 + getPaddingStart() + getPaddingEnd();
        mPaddingLeft = horizontalPadding - getPaddingEnd() - circleRadius - circleStrokeWidth;
        return;
    
    maxProgress = 100;
    minProgress = 0;
    circleRadius = 20;
    circleStrokeWidth = 5;
    lineHeight = 5;
    backgroundColor = Color.parseColor("#F0F0F0");
    colorTransition = new ColorTransition(Color.WHITE, Color.RED);
    circleStrokeColor = Color.WHITE;

    horizontalPadding = circleRadius * 2 + circleStrokeWidth * 2 + getPaddingStart() + getPaddingEnd();
    mPaddingLeft = horizontalPadding - getPaddingEnd() - circleRadius - circleStrokeWidth;

接下来是onMeasure和onDraw，由于我的应用场景宽高已经固定好了，所以没有写onMeasure，有需求的朋友可以自己实现一下～
而绘制的思路很简单：

1. 先绘制一条背景色的线，线的高度由外部指定。（设置StrokeCap为ROUND）
2. 再绘制一条前景色的线，线高度同样由外部指定，这里我读取的是同一个属性lineHeight，也可以根据需求不同设置不一样的高度;p
3. 接下来绘制seekBar的圆，这里border也直接使用drawCircle来实现，先绘制border。(circleRadius + circleStrokeWidth / 2f)
4. 最后绘制中间的圆

onDraw:

@Override
protected void onDraw(Canvas canvas) 
    final int width = (int) (getMeasuredWidth() - horizontalPadding);
    final int height = getMeasuredHeight();

    paint.setColor(backgroundColor);
    paint.setStrokeWidth(lineHeight);
    paint.setStyle(Paint.Style.FILL_AND_STROKE);
    paint.setStrokeCap(Paint.Cap.ROUND);
    canvas.drawLine(mPaddingLeft, height >> 1, mPaddingLeft + width, height >> 1, paint);

    //float percentage = progress / maxProgress;
    int currColor = colorTransition.getValue(percentage);
    paint.setColor(currColor);
    canvas.drawLine(mPaddingLeft, height >> 1, mPaddingLeft + width * percentage, height >> 1, paint);

    // draw circle border
    paint.setColor(circleStrokeColor);
    canvas.drawCircle(mPaddingLeft + width * percentage, height >> 1, circleRadius + (circleStrokeWidth / 2f), paint);
    // draw circle inside color
    paint.setColor(currColor);
    canvas.drawCircle(mPaddingLeft + width * percentage, height >> 1, circleRadius, paint);

最后，处理一下onTouch事件。思路也很简单，从down、move、up事件中判断一下是否为横向滚动，是的话计算一下距离，更改progress进度并通知View重新绘制即可：

private float downX;
private float downY;
@Override
public boolean onTouchEvent(MotionEvent event) 
    boolean intercept = false;
    switch (event.getAction()) 
        case MotionEvent.ACTION_DOWN:
            downX = event.getX();
            downY = event.getY();
            intercept = true;
            break;
        case MotionEvent.ACTION_MOVE:
            float moveX = event.getX();
            float moveY = event.getY();
            float xMove = Math.abs(moveX - downX) - Math.abs(moveY - downY);
            if (xMove > 0f) 
                float hX = moveX - downX;
                boolean toLeft = hX < 0.0f;
                float movePercent = Math.abs(hX) / getMeasuredWidth();
                if (percentage < 1.0f && !toLeft) 
                    percentage += movePercent;
                 else if (percentage > 0f && toLeft) 
                    percentage -= movePercent;
                

                if (percentage < 0f) percentage = 0f;
                if (percentage > 1f) percentage = 1f;

                progress = (int) Math.floor(percentage * maxProgress);
            
            intercept = true;
            downX = moveX;
            downY = moveY;
            postInvalidate();

            if (null != mListener && beforeProgress != getProgress()) 
                beforeProgress = getProgress();
                mListener.onProgress(getProgress());
            
            break;
        case MotionEvent.ACTION_UP:
            break;
    
    return intercept || super.onTouchEvent(event);
    //return true;


@Override
public boolean dispatchTouchEvent(MotionEvent event) 
    getParent().requestDisallowInterceptTouchEvent(true);
    return super.dispatchTouchEvent(event);

OK，一个复制即用的自定义SeekBar便完成了。比官方原版的SeekBar使用起来顺眼多了(｢・ω・)｢

(欢迎下载Demo玩一玩！Demo地址)