方法一

#import "DrawView.h"

@implementation DrawView

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        //設定 背景為clear
        self.backgroundColor = [UIColor clearColor];
        self.opaque = NO;
    }
    return self;
}

- (void)drawRect:(CGRect)rect {

    [[UIColor colorWithWhite:0
 
 alpha:0.5] setFill];
    //半透明區域
    UIRectFill(rect);

    //透明的區域
    CGRect holeRection = CGRectMake(100, 200, 200, 200);
    /** union: 並集
     CGRect CGRectUnion(CGRect r1, CGRect r2)
     返回並集部分rect
     */

    /** Intersection: 交集
     CGRect CGRectIntersection(CGRect r1, CGRect r2)
     返回交集部分rect
     */
    CGRect holeiInterSection = CGRectIntersection(holeRection, rect);
    [[UIColor clearColor] setFill];

    //CGContextClearRect(ctx, <#CGRect rect#>)
 

    //繪製
    //CGContextDrawPath(ctx, kCGPathFillStroke);
    UIRectFill(holeiInterSection);

}

直接新增使用就行

    DrawView *drawView = [[DrawView alloc] initWithFrame:[UIScreen mainScreen].bounds];
    [self.view addSubview:drawView];

方法二

#import "DrawViewArc.h"

@implementation DrawViewArc

- (instancetype)initWithFrame:(CGRect
 
)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
        self.opaque = NO;
    }
    return self;
}

- (void)drawRect:(CGRect)rect {
    //中間鏤空的矩形框
    CGRect myRect =CGRectMake(100,100,200, 200);

    //背景
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:0];
    //鏤空
    UIBezierPath *circlePath = [UIBezierPath bezierPathWithOvalInRect:myRect];
    [path appendPath:circlePath];
    [path setUsesEvenOddFillRule:YES];

    CAShapeLayer *fillLayer = [CAShapeLayer layer];
    fillLayer.path = path.CGPath;
    fillLayer.fillRule = kCAFillRuleEvenOdd;
    fillLayer.fillColor = [UIColor whiteColor].CGColor;
    fillLayer.opacity = 0.5;
    [self.layer addSublayer:fillLayer];

}

也是直接呼叫就行

方法三

寫到需要新增 透明圓的 view裡

- (void)addArc {
    //中間鏤空的矩形框
    CGRect myRect =CGRectMake(100,100,200, 200);

    //背景
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:[UIScreen mainScreen].bounds cornerRadius:0];
    //鏤空
    UIBezierPath *circlePath = [UIBezierPath bezierPathWithOvalInRect:myRect];
    [path appendPath:circlePath];
    [path setUsesEvenOddFillRule:YES];

    CAShapeLayer *fillLayer = [CAShapeLayer layer];
    fillLayer.path = path.CGPath;
    fillLayer.fillRule = kCAFillRuleEvenOdd;
    fillLayer.fillColor = [UIColor whiteColor].CGColor;
    fillLayer.opacity = 0.5;
    [self.view.layer addSublayer:fillLayer];

}

呼叫
[self addArc];

方法四

#import "DrawArc.h"

@implementation DrawArc

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
        self.opaque = NO;
    }
    return self;
}

- (void)drawRect:(CGRect)rect {
    //中間鏤空的矩形框
    CGRect myRect =CGRectMake(100,100,200, 200);

    CGContextRef ctx = UIGraphicsGetCurrentContext();

    //背景色
    //[[UIColor colorWithPatternImage:[UIImage imageNamed:@"1.jpg"]] set];
    [[UIColor colorWithWhite:0 alpha:0.5] set];
    CGContextAddRect(ctx, rect);
    CGContextFillPath(ctx);

    //設定清空模式
    /**
     kCGBlendModeClear,
     kCGBlendModeCopy,
     kCGBlendModeSourceIn,
     kCGBlendModeSourceOut,
     kCGBlendModeSourceAtop,
     kCGBlendModeDestinationOver,
     kCGBlendModeDestinationIn,
     kCGBlendModeDestinationOut,
     kCGBlendModeDestinationAtop,
     kCGBlendModeXOR,
     kCGBlendModePlusDarker,
     kCGBlendModePlusLighter
     */
    CGContextSetBlendMode(ctx, kCGBlendModeClear);

    //畫圓
    CGContextAddEllipseInRect(ctx, myRect);

    //填充
    CGContextFillPath(ctx);

}