利用Android画圆弧canvas.drawArc()实例详解

public void drawArc(@NonNull RectF oval, float startAngle, float sweepAngle, boolean useCenter,
  @NonNull Paint paint) {
 drawArc(oval.left, oval.top, oval.right, oval.bottom, startAngle, sweepAngle, useCenter,
  paint);
 }

 /**
  * 这是一个居中的圆
  */
 float x = (getWidth() - getHeight() / 2) / 2;
 float y = getHeight() / 4;

 RectF oval = new RectF( x, y,
  getWidth() - x, getHeight() - y); 

canvas.drawArc(oval,-90,120,false,mPaint);

canvas.drawArc(oval,90,110,false,mPaint);

//设置为-180的时候也是这样
canvas.drawArc(oval,180,140,false,mPaint);

//设置为360的时候也是这样
canvas.drawArc(oval,0,140,false,mPaint);

  /**
  *这里我是偷懒了，建议不要在onDraw()方法里初始化对象
  */
  Paint p = new Paint();//这个是画矩形的画笔，方便大家理解这个圆弧
  p.setStyle(Paint.Style.STROKE);
  p.setColor(Color.RED);

  mPaint.setAntiAlias(true);//取消锯齿
  mPaint.setStyle(Paint.Style.FILL);//设置画圆弧的画笔的属性为描边(空心)，个人喜欢叫它描边，叫空心有点会引起歧义
  mPaint.setStrokeWidth(mCircleWidth);
  mPaint.setColor(Color.CYAN);

  /**
   * 这是一个居中的圆
   */
  float x = (getWidth() - getHeight() / 2) / 2;
  float y = getHeight() / 4;

  RectF oval = new RectF( x, y,
    getWidth() - x, getHeight() - y);

  canvas.drawArc(oval,360,140,false,mPaint);//画圆弧，这个时候，绘制没有经过圆心
  canvas.drawRect(oval, p);//画矩形

//当我们设置为true的时候，绘制的时候就经过圆心了
canvas.drawArc(oval,360,140,true,mPaint);

//当我们设置为true的时候，绘制的时候就经过圆心了
canvas.drawArc(oval,360,140,true,mPaint);

public class CustomProgress extends View{

 private Paint mPaint;

 /**
  * 圆的宽度
  */
 private int mCircleWidth = 3;

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

 public CustomProgress(Context context, AttributeSet attrs) {
  this(context, attrs, 0);
 }

 public CustomProgress(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  mPaint = new Paint();
 }

 @Override
 protected void onDraw(Canvas canvas) {
  mPaint.setAntiAlias(true);//取消锯齿
  mPaint.setStyle(Paint.Style.FILL);
  mPaint.setStrokeWidth(mCircleWidth);
  mPaint.setColor(Color.CYAN);

  /**
   * 这是一个居中的圆
   */
  float x = (getWidth() - getHeight() / 2) / 2;
  float y = getHeight() / 4;

  RectF oval = new RectF( x, y,
    getWidth() - x, getHeight() - y); 

  canvas.drawArc(oval,360,140,true,mPaint);
 }
}