ios--异步下载、显示图片

爱被打了一巴掌 2022-08-10 15:49 202阅读 0赞

原文转自：[http://blog.csdn.net/wbw1985/article/details/7622926][http_blog.csdn.net_wbw1985_article_details_7622926]

下载图片并异步显示更新数据到前台，我们可以有很多种方法，在IOS中提到了两种方法如下：

需要定义一个ImageView和一个Button如下

@property (retain, nonatomic) IBOutlet UIImageView *imageView;  
    - (IBAction)download:(id)sender;
    
    第一种方法： 
    - (IBAction)download:(id)sender {  
        NSURL *url = [NSURL URLWithString:@"http://img6.cache.netease.com/cnews/2012/6/1/20120601085505e3aba.jpg"];  
          
        [NSThread detachNewThreadSelector:@selector(dowork:) toTarget:self withObject:url];  
          
    }
    其中调用了dowork函数  
    -(void) dowork: (NSURL*) url{  
        NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];  
        NSError *error;  
          
        NSURLRequest *request = [NSURLRequest requestWithURL:url];  
        NSHTTPURLResponse *response;  
          
        NSData* retData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];  
          
        if (response.statusCode == 200) {  
            UIImage* img = [UIImage imageWithData:retData];  
            [self   performSelectorOnMainThread:@selector(refreshUI:) withObject:img waitUntilDone:YES];  
              
        }  
        NSLog(@"d %d", response.statusCode);  
        [pool drain];  
          
    } 
    dowork方法中下载完成后通知UI更新，函数如下  
    -(void) refreshUI:(UIImage* ) img{  
        self.imageView.image = img;  
    }  
     
    第二种方法使用GCD来更新UI  
    - (IBAction)download:(id)sender {  
      
        [self blockWork];  
          
    }  
    Button调用block方法来下载并回调async来异步更新UI来显示图片  
    -(void)blockWork{  
        dispatch_queue_t queue;  
        queue = dispatch_queue_create("com.example.operation", NULL);  
        dispatch_async(queue, ^{  
            NSString *urlString = @"http://img6.cache.netease.com/cnews/2012/6/1/20120601085505e3aba.jpg";  
            NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];  
              
            UIImage *imge = [UIImage imageWithData:imageData];  
              
            dispatch_async(dispatch_get_main_queue(), ^{  
                self.imageView.image = imge;  
            });  
              
        });

[http_blog.csdn.net_wbw1985_article_details_7622926]: http://blog.csdn.net/wbw1985/article/details/7622926