Android自定义View如何实现圆环进度条

/**
 * 圆环进度条
 */
public class RoundProgressBar extends View {
 //绘制矩形区域
 private RectF rectF;
 //起始角度
 private float startAngle;
 //扫过角度
 private float sweepAngle;
 //画笔
 private Paint paint;
 //默认控件大小
 private int defoutSize;
 //默认线条宽度
 private int defoutLine;
 private int strokeWidth;

 private PointF pointF = new PointF();


 public RoundProgressBar(Context context) {
  super(context);
  initData();
 }

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

 /**
  * 参数初始化
  */
 private void initData() {
  startAngle = 0;
  sweepAngle = 0;
  defoutSize = 400;
  defoutLine = 20;
  strokeWidth = 20;

  rectF = new RectF();

  //抗锯齿画笔
  paint = new Paint(Paint.ANTI_ALIAS_FLAG);
  paint.setColor(Color.GRAY);
  paint.setStrokeWidth(defoutLine);
  //笔帽样式
  paint.setStrokeCap(Paint.Cap.ROUND);
  paint.setStyle(Paint.Style.STROKE);
 }

 /**
  * xml -----> 提供可绘制位置
  *
  * @param widthMeasureSpec 宽
  * @param heightMeasureSpec 高
  */
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  setMeasuredDimension(defoutSize, defoutSize);
 }

 /**
  * 当大小时改变回调
  *
  * @param w
  * @param h
  * @param oldw
  * @param oldh
  */
 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);

  pointF.x = w >> 1;
  pointF.y = h >> 1;

  rectF.top = strokeWidth >> 1;
  rectF.bottom = h - (strokeWidth >> 1);
  rectF.left = strokeWidth >> 1;
  rectF.right = w - (strokeWidth >> 1);

 }

 /**
  * 绘制
  *
  * @param canvas
  */
 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);

  //画布旋转
  paint.setColor(Color.GRAY);
  canvas.rotate(135, pointF.x, pointF.y);
  //绘制圆环
  canvas.drawArc(rectF, startAngle, 270, false, paint);

  paint.setColor(Color.RED);
  canvas.drawArc(rectF, startAngle, sweepAngle, false, paint);

 }

 public void setProgress(float index) {
 //防止数值越界
  if (index > 1 || index < 0) {
   return;
  }
  ValueAnimator valueAnimator = ValueAnimator.ofFloat(0, index);
  valueAnimator.setDuration(3000);
  valueAnimator.setInterpolator(new DecelerateInterpolator());
  valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
   @Override
   public void onAnimationUpdate(ValueAnimator animation) {
    sweepAngle = (float) animation.getAnimatedValue() * 270;
    //重写绘制
    invalidate();
   }
  });
  valueAnimator.start();

 }
}

progressView.setProgress(0.8f);