［自定义组件之四］利用Quartz2D实现圆形图片显示

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

-(UIImage*)CircleImg
{
    /*添加图片*/
    UIImage* img = [UIImage imageNamed:@"J罗.jpg"];
    CGFloat borderWith = 20.0f;
    CGSize imgSize = CGSizeMake(img.size.width + borderWith, img.size.height + borderWith);
    CGFloat bigRadius = imgSize.width * 0.5;/*外圆半径*/
    CGFloat smallRadius = bigRadius - borderWith;/*内圆半径*/
    
    UIGraphicsBeginImageContextWithOptions(imgSize, NO, 0.0f);
    CGContextRef ctx = UIGraphicsGetCurrentContext();/*得到图片的上下文*/
    CGContextAddArc(ctx, bigRadius, bigRadius, bigRadius - borderWith / 2, 0, M_PI * 2, 0);/*添加大圆*/
    CGContextSetStrokeColorWithColor(ctx, [[UIColor redColor] CGColor]);
    CGContextSetLineWidth(ctx, borderWith);/*设置线宽*/
    CGContextStrokePath(ctx);/*画大圆*/
    
    CGContextAddArc(ctx, bigRadius, bigRadius, smallRadius, 0, M_PI * 2, 0);/*添加小圆*/
    CGContextClip(ctx);/*剪裁，后面的受影响*/
    CGRect rect = CGRectMake(borderWith, borderWith, img.size.width, img.size.height);
    [img drawInRect: rect];/*画图*/
    UIImage* img2 = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img2;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    /*用的是实际尺寸370，要不画出的border也会缩放*/
    UIImageView* imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 20, 370, 370)];
    imgView.image = [self CircleImg];
    [self.view addSubview:imgView];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

说是这个方法可扩展性高，比如添加个边框之类的。

注意大圆的半径，要减去边框的一半，否则边框显示不全。

参考：http://www.360doc.com/content/15/0128/17/20918780_444509231.shtml