给出 URL 时下载文件 - iPhone sdk

Question

如果给出 URL，是否可以从 Internet 下载文件并将其存储在文档目录中？我浏览了苹果开发者网站上的一些文件。它说它可以使用 NSURLDownload，但它不能在 iOS 中使用。因此，只有在 iOS 的情况下才应该使用 NSURLConnection 来完成。所以，有人帮我从给定的 URL 下载文件（甚至是 HTML 页面）。提前致谢。

Answer 1

我认为ASIHTTPRequest 库会帮助你:)

ASIWebPageRequest

ASIHTTPRequest 中包含的 ASIWebPageRequest 类可让您下载完整的网页，包括图像和样式表等外部资源。

来自allseeing-i.com的代码示例

- (IBAction)loadURL:(NSURL *)url
{
   // Assume request is a property of our controller
   // First, we'll cancel any in-progress page load
   [[self request] setDelegate:nil];
   [[self request] cancel];

   [self setRequest:[ASIWebPageRequest requestWithURL:url]];
   [[self request] setDelegate:self];
   [[self request] setDidFailSelector:@selector(webPageFetchFailed:)];
   [[self request] setDidFinishSelector:@selector(webPageFetchSucceeded:)];

   // Tell the request to embed external resources directly in the page
   [[self request] setUrlReplacementMode:ASIReplaceExternalResourcesWithData];

   // It is strongly recommended you use a download cache with ASIWebPageRequest
   // When using a cache, external resources are automatically stored in the cache
   // and can be pulled from the cache on subsequent page loads
   [[self request] setDownloadCache:[ASIDownloadCache sharedCache]];

   // Ask the download cache for a place to store the cached data
   // This is the most efficient way for an ASIWebPageRequest to store a web page
   [[self request] setDownloadDestinationPath:
      [[ASIDownloadCache sharedCache] pathToStoreCachedResponseDataForRequest:[self request]]];

   [[self request] startAsynchronous];
}

- (void)webPageFetchFailed:(ASIHTTPRequest *)theRequest
{
   // Obviously you should handle the error properly...
   NSLog(@"%@",[theRequest error]);
}

- (void)webPageFetchSucceeded:(ASIHTTPRequest *)theRequest
{
   NSString *response = [NSString stringWithContentsOfFile:
      [theRequest downloadDestinationPath] encoding:[theRequest responseEncoding] error:nil];
   // Note we're setting the baseURL to the url of the page we downloaded. This is important!
   [webView loadHTMLString:response baseURL:[request url]];
}

Answer 2

这是一个从服务器获取图像并将其保存到文件的示例。

创建实例变量

NSMutableData *activeDownload;
NSURLConnection *imageConnection;

现在创建您的连接

NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
NSURL *url = [[NSURL alloc] initWithString:@"URL TO FILE"];
[request setURL:url];
[url release];
url = nil;

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

处理接收数据

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [self.activeDownload appendData:data];
}

传输完成，保存数据

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *fileName = [[paths objectAtIndex:0] stringByAppendingPathComponent:self.imageFileName];

[self.activeDownload writeToFile:fileName atomically:YES];

self.activeDownload = nil;
self.imageConnection = nil;
}

还有一些我没有展示的代码（属性等），但我认为这应该可以为您提供足够的帮助。

Answer 3

是的，您可以使用 NSURLConnection 来实现。您需要向 URL 发出请求。像这样的东西。

NSString *strDownloadURL = @"File URL";
NSMutableURLRequest *request  = [[NSMutableURLRequest alloc]initWithURL:[NSURL URLWithString:strDownloadURL]];

Connection *con = [[[Connection alloc] init];
con.delegate=self;
[[[NSURLConnection alloc]initWithRequest:request delegate:con] autorelease];

现在，在 Connection Delegate Method didReceiveData 中将 NSData 分配给全局变量。

- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data {
  if (receivedData != nil) {
    [receivedData appendData:data];
  } else {
    receivedData = [[NSMutableData alloc] initWithData:data];
  }
}

最后，在连接委托方法“connectionDidFinishLoading”中，您应该拥有 NSData 格式的文件数据。所以将它存储在类似这样的文档目录中。

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
  [receivedData writeToFile:DocumentPathtoSaveFile atomically:YES];
}