后台加载图片

-(void)setImageWithURL:(NSURL *) url{
    
    
    //加载网络图片的时候应该开启一个线程，不然加载的时候会阻塞
    [self performSelectorInBackground:@selector(loadData:) withObject:url];
    
    
}


-(void)loadData:(NSURL *) url{

    @autoreleasepool {
        NSData *data = [NSData dataWithContentsOfURL:url];
        UIImage *image = [UIImage imageWithData:data];
        
        //在主线程上执行setImage方法
        [self performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:YES];
    }
}