UIButton 加载网络图片

以后就可以 用这个分类   UIButton轻松加载网络图片了，

UIButton+WebCache.h

#import <UIKit/UIKit.h>

@interface UIButton (WebCache)
- (void)xr_setButtonImageWithUrl:(NSString *)urlStr;
@end

UIButton+WebCache.m

#import "UIButton+WebCache.h"

@implementation UIButton (WebCache)
- (void)xr_setButtonImageWithUrl:(NSString *)urlStr {

    NSURL * url = [NSURL URLWithString:urlStr];
    // 根据图片的url下载图片数据
    dispatch_queue_t xrQueue = dispatch_queue_create("loadImage", NULL); // 创建GCD线程队列
    dispatch_async(xrQueue, ^{
        // 异步下载图片
        UIImage * img = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];
        // 主线程刷新UI
        dispatch_async(dispatch_get_main_queue(), ^{
            [self setImage:img forState:UIControlStateNormal];
        });
    });  

}  

@end