方法一：

新建testView

- (void)drawRect:(CGRect)rect {
    // Start by filling the area with the blue color

    [[UIColor colorWithWhite:0.0f alpha:0.5f] setFill];//陰影效果 根據透明度來設計
    UIRectFill( rect );
    CGRect holeRectIntersection = CGRectIntersection( holeRect, rect );
    [[UIColor clearColor] setFill];
    UIRectFill( holeRectIntersection );
}
 

ViewController中

UIImage *image = [UIImageimageNamed:@"photo3.jpg"];
    [self.view.layersetContents:(id)[imageCGImage]];

    testView *testVW = [[testViewalloc]initWithFrame:self.view.frame];
    testVW.backgroundColor = [UIColorclearColor];
    testVW.opaque =NO;
    [self.viewaddSubview:testVW];
 

view 的背景色一定要設定成clearColor,opaue一定要設定no；

方法二：

CGRect myRect =CGRectMake(100,100,200, 200);
    int radius = myRect.size.width/2.0;
    UIBezierPath *path = [UIBezierPathbezierPathWithRoundedRect:CGRectMake(0,0, backView.bounds.size.width, backView.bounds.size.height)cornerRadius:0];
    UIBezierPath *circlePath = [UIBezierPathbezierPathWithRoundedRect:CGRectMake(100
 
,100,2.0*radius,2.0*radius)cornerRadius:radius];
    [path appendPath:circlePath];
    [path setUsesEvenOddFillRule:YES];

    CAShapeLayer *fillLayer = [CAShapeLayerlayer];
    fillLayer.path = path.CGPath;
    fillLayer.fillRule =kCAFillRuleEvenOdd;
    fillLayer.fillColor = [UIColorgrayColor].CGColor;
    fillLayer.opacity =0.5;
    [backView.layeraddSublayer:fillLayer];