ios画圆,圆形进度条

     UIView *_demoView=[[UIView alloc]init];
    _demoView.frame=CGRectMake(100, 230, 50, 50);
    [self.view addSubview:_demoView];
    
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.frame = _demoView.bounds;
    shapeLayer.strokeEnd = 0.7f;
    shapeLayer.strokeStart = 0.1f;
    
    UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:_demoView.bounds];
    
    shapeLayer.path = path.CGPath;
    
    shapeLayer.fillColor = [UIColor clearColor].CGColor;
    shapeLayer.lineWidth = 2.0f;
    shapeLayer.strokeColor = [UIColor redColor].CGColor;
    
    [_demoView.layer addSublayer:shapeLayer];