Object-c / iOS：如何使用ASynchronous从URL获取数据？

NSURL *theURL =  [[NSURL alloc]initWithString:@"http://someurllink.PHP" ];
NSURLrequest *therequest=[NSURLrequest requestWithURL:theURL
                                          cachePolicy:NSURLrequestuseProtocolCachePolicy
                                          timeoutInterval:60.0];
NSData *returnData = [NSURLConnection sendSynchronousrequest:therequest returningResponse:nil error:nil]; 
NSString *listFile = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];   
self.plist = [listFile propertyList];
[self.tableView reloadData];
[listFile autorelease];

简短的答案：你可以使用

+ (NSURLConnection *)connectionWithrequest:(NSURLrequest *)request delegate:(id)delegate;

请参阅NSURLConnectionDelegate获取非正式委托协议(所有方法都是可选的)

长答案：

异步下载数据并不像同步方法那么简单.首先,您必须创建自己的数据容器,例如文件容器

//under documents folder/temp.xml
file = [[SomeUtils getDocumentsDirectory] StringByAppendingPathComponent:@"temp.xml"]
NSFileManager *fileManager = [NSFileManager defaultManager];
if(![fileManager fileExistsAtPath:file]) {
  [fileManager createFileAtPath:file contents:nil attributes:nil];
}

连接到服务器时：

[NSURLConnection connectionWithrequest:myrequest delegate:self];

您必须使用您异步接收的数据填充容器：

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
  NSFileHandle *fileHandle = [NSFileHandle fileHandleForupdatingAtPath:file];
  [fileHandle seekToEndOfFile];
  [fileHandle writeData:data];
  [fileHandle closeFile];
}

您必须管理遇到的错误：

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

如果要捕获服务器响应：

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NShttpURLResponse *)response

连接完成加载时处理：

- (void)connectionDidFinishLoading:(NSURLConnection *)connection