Android实现圆弧形渐变色进度条

效果图：

我写的这篇博客个人感觉非常的不详细，这也是根据UI设计的，不过大家掌握下文所点出来的重点方法也可以将其绘制出来，这里就不详细介绍绘制流程了

UI分析：

这个UI细分为表盘刻度、进度条底色、进度条渐变色、最外层那个实心圆球和文字描述。接下来就逐个实现

一、绘制表盘刻度

1、绘制表盘的刻度主要是用了画布的旋转来进行绘制
利用canvas.rotate()方法来旋转画布。利用canva.drawText()方法绘制文字，最后canvas.restore()释放画布让其回到原来的位置

/**
     * 旋转画布画刻度
     * @param canvas 画布
     */
    private void paintPercentText(Canvas canvas){
        paint.setTextSize(percentTextSize);
        paint.setColor(pinkColor);
        paint.setStrokeWidth(1);
        paint.setTextAlign(Paint.Align.CENTER);
        for (int i=0;i<=10;i++){
            //保存画布
            canvas.save();
            //旋转角度，第一个参数是旋转的角度、第二个参数和第三个参数是旋转中心点x和y
            canvas.rotate((float) (spaceAngle * i + -135 + spaceAngle), width / 2, radius);
            //画文字
            canvas.drawText(i * 10 + "", width / 2,  outerArcWidth + insideArcWidth + spaceWidth * 2, paint);
            canvas.restore();
        }
    }

二、绘制进度条底色

绘制进度条的底色主要用paint.setStrokeCap(Paint.Cap.ROUND)将画笔设置为圆角和canvas.drawArc()方法，这里就需要计算好矩形框以及起始的角度和结束的角度

 /**画两条线的底色*/
    private void paintPercentBack(Canvas canvas){
        paint.setColor(grayColor);
        paint.setStrokeWidth(outerArcWidth);//outerArcWidth
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeCap(Paint.Cap.ROUND);//设置为圆角
        paint.setAntiAlias(true);
        //绘制最外层圆条底色
        outerArcRadius=radius-outerArcWidth;
        outerArea= new RectF(width/2 - outerArcRadius, radius - outerArcRadius, width/2  + outerArcRadius, radius + outerArcRadius);
        canvas.drawArc(outerArea,
                (float) (180 - floatAngel),
                (float) (180 + 2 * floatAngel), false, paint);
        //绘制里层大宽度弧形
        paint.setColor(pinkColor);
        paint.setStrokeWidth(insideArcWidth);
        paint.setStyle(Paint.Style.STROKE);
        canvas.drawArc(new RectF(width / 2 - insideArcRadius, radius - insideArcRadius, width / 2 + insideArcRadius, radius + insideArcRadius),
                (float) (180 - floatAngel),
                (float) (180 + 2 * floatAngel), false, paint);

    }

三、绘制进度条的渐变色

绘制渐变色的进度条主要是用到了setXfermode()方法setShader()方法和来进行绘制，setXfermode方法选择PorterDuff.Mode.SRC_ATOP是用于将绘制的内容显示在第一次绘制内容之上，（不过这个绘制应该在Bitmap上，最后的整体代码上有），setShader方法用于渐变色控制

四、绘制最外层的的原点

最外层的原点需要不断的计算坐标，在这里用到的方法主要是PathMeasure类，将要绘制的圆弧，加入一个路径，
private float[] pos; // 当前点的实际位置
private float[] tan; // 当前点的tangent值,
PathMeasure measure = new PathMeasure(orbit, false);
measure.getPosTan(measure.getLength() * 1, pos, tan);
获取路径的终点的正切值和坐标，然后根据坐标点绘制实心小园球

 private void paintPercent(double percent,double aimPercent,Canvas canvas){
        double roateAngel=percent*0.01*225;
        shaderPaint.setColor(yellowColor);
        shaderPaint.setStrokeCap(Paint.Cap.ROUND);
        shaderPaint.setAntiAlias(true);
        shaderPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_ATOP));//shaderPaint.setColor(yellowColor);
        if (aimPercent>=0&&aimPercent<=20){
        }else if (aimPercent>20&&aimPercent<=60){
            int colorSweep[] = { yellowColor,pinkRedColor };
            float position[]={
  0.5f,0.7f};
            SweepGradient sweepGradient=new SweepGradient(width / 2, radius, colorSweep, position);
            shaderPaint.setShader(sweepGradient);
        }else if (aimPercent>60&&aimPercent<=90){
            int colorSweep[] = { yellowColor,pinkRedColor,redColor };
            float position[]={
  0.5f,0.7f,0.8f};
            SweepGradient sweepGradient=new SweepGradient(width / 2, radius, colorSweep, position);
            shaderPaint.setShader(sweepGradient);
        }else if (aimPercent>90){
            int colorSweep[] = {deepRedColor, yellowColor,yellowColor,pinkRedColor,redColor, deepRedColor};
            float position[]={
  0.2f,0.4f,0.5f,0.7f,0.9f,1.0f};
            SweepGradient sweepGradient=new SweepGradient(width / 2, radius, colorSweep, position);
            shaderPaint.setShader(sweepGradient);
        }
        if (aimPercent<=10){
  //目的是为了
            drawInsideArc((float) (180 - floatAngel), (float) roateAngel, canvas);
            drawOuterAcr((float) (180 - floatAngel), (float) roateAngel, canvas,mBitmapBackDeepRed,yellowColor);
        }else if (aimPercent>10&&aimPercent<=20){
            drawInsideArc((float) (180 - floatAngel), (float) roateAngel, canvas);
            drawOuterAcr((float) (180 - floatAngel), (float) roateAngel, canvas,mBitmapBackDeepRed,yellowColor);
        }else if (aimPercent>20&&aimPercent<=60){
            drawInsideArc((float) (180 - floatAngel), (float) (roateAngel-(spaceAngle-floatAngel)), canvas);
            drawOuterAcr((float) (180 - floatAngel), (float) (roateAngel - (spaceAngle - floatAngel)), canvas,mBitmapBackDeepRed,pinkRedColor);
        }else if (aimPercent>60&&aimPercent<=90){
            drawInsideArc((float) (180 - floatAngel), (float) (roateAngel-(spaceAngle-floatAngel)), canvas);
            drawOuterAcr((float) (180 - floatAngel), (float) (roateAngel - (spaceAngle - floatAngel)),canvas,mBitmapBackDeepRed,redColor);
        }