Question

我有一个使用URL显示图像的UIImageView，我有一个下载按钮，显示一个UIActionSheet，然后使用URL下载文件我想知道如何编写下载部分的代码使用NSURLConnection。

- (IBAction)DownloadClick:(id)sender {

    UIActionSheet *Action = [[UIActionSheet alloc]
                         initWithTitle:@"Options" 
                         delegate:self 
                         cancelButtonTitle:@"Cancel" 
                         destructiveButtonTitle:nil
                         otherButtonTitles:@"Download", nil];

    [Action showInView:self.view];
}

-(void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {

    if (buttonIndex == 0) {  //The Download code will go here This is where i need ur help


          }

Url保存在名为“Url”的字符串中。

Answer 1

利用异步请求进行图像下载。它还可以帮助您识别图像下载过程中的错误。

 NSURL* url = [NSURL URLWithString:@"http://imageAddress.com"];
 NSURLRequest* request = [NSURLRequest requestWithURL:url];


[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse * response,
    NSData * data,
    NSError * error) {
if (!error){
            UIImage* image = [[UIImage alloc] initWithData:data];
           // do whatever you want with image
           }

}];

Answer 2

我不认为你为此尝试了谷歌。无论如何，这是你的代码，不要忘记添加 NSURLConnectionDataDelegate ，

-(void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (buttonIndex == 0) {  //The Download code will go here This is where i need ur help

    //-------------------------------------------------------
    NSURL *url = [NSURL URLWithString:@"your_data_url"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url
                                             cachePolicy:NSURLRequestUseProtocolCachePolicy
                                         timeoutInterval:60.0];

    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

    if (connection) {
        NSLog(@"succeed...");
    } else {
        NSLog(@"Failed...");
    }
    //-------------------------------------------------------------------
  }
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{

}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{

}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{

}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{

}

Answer 3

如果您需要同步下载，可以尝试以下代码：

NSURL *imageUrl = [NSURL URLWithString:@"http://site.com/imageName.ext"];
NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];
UIImage *image = [[UIImage alloc] initWithData:imageData];

现在你有了一个可以使用的图像。

如果您需要异步请求，我建议您阅读NSURLConnectionDataDelegate，以帮助您处理文件下载。

使用NSURLConnection下载

3 个答案: