iOS學習——iOS網絡通信http之NSURLConnection(八)

      移動網際網路時代，網絡通信已是手機終端必不可少的功能。我們的應用中也必不可少的使用了網絡通信，增強用戶端與伺服器互動。這一篇提供了使用NSURLConnection實作http通信的方式。

          NSURLConnection提供了異步請求、同步請求兩種通信方式。

1、異步請求

       iOS5.0 SDK NSURLConnection類新增的sendAsynchronousRequest:queue:completionHandler:方法，進而使iOS5支援兩種異步請求方式。我們先從新增類開始。

1）sendAsynchronousRequest

iOS5.0開始支援sendAsynchronousReques方法，方法使用如下：

- (void)httpAsynchronousRequest{      NSURL *url = [NSURL URLWithString:@"http://url"];          NSString *post=@"postData";          NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];      NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];     [request setHTTPMethod:@"POST"];     [request setHTTPBody:postData];     [request setTimeoutInterval:10.0];          NSOperationQueue *queue = [[NSOperationQueue alloc]init];     [NSURLConnection sendAsynchronousRequest:request                                        queue:queue                            completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){                                if (error) {                                    NSLog(@"Httperror:%@%d", error.localizedDescription,error.code);                                }else{                                                                        NSInteger responseCode = [(NSHTTPURLResponse *)response statusCode];                                                                        NSString *responseString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];                                                                        NSLog(@"HttpResponseCode:%d", responseCode);                                    NSLog(@"HttpResponseBody %@",responseString);                                }                            }];       }       

      sendAsynchronousReques可以很容易地使用NSURLRequest接收回調，完成http通信。

2）connectionWithRequest

iOS2.0就開始支援connectionWithRequest方法，使用如下：

- (void)httpConnectionWithRequest{          NSString *URLPath = [NSString stringWithFormat:@"http://url"];     NSURL *URL = [NSURL URLWithString:URLPath];     NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL];     [NSURLConnection connectionWithRequest:request delegate:self];      }  - (void)connection:(NSURLConnection *)theConnection didReceiveResponse:(NSURLResponse *)response {         NSInteger responseCode = [(NSHTTPURLResponse *)response statusCode];     NSLog(@"response length=%lld  statecode%d", [response expectedContentLength],responseCode); }   // A delegate method called by the NSURLConnection as data arrives.  The // response data for a POST is only for useful for debugging purposes, // so we just drop it on the floor. - (void)connection:(NSURLConnection *)theConnection didReceiveData:(NSData *)data {     if (mData == nil) {         mData = [[NSMutableData alloc] initWithData:data];     } else {         [mData appendData:data];     }     NSLog(@"response connection"); }  // A delegate method called by the NSURLConnection if the connection fails. // We shut down the connection and display the failure.  Production quality code // would either display or log the actual error. - (void)connection:(NSURLConnection *)theConnection didFailWithError:(NSError *)error {          NSLog(@"response error%@", [error localizedFailureReason]); }  // A delegate method called by the NSURLConnection when the connection has been // done successfully.  We shut down the connection with a nil status, which // causes the image to be displayed. - (void)connectionDidFinishLoading:(NSURLConnection *)theConnection {     NSString *responseString = [[NSString alloc] initWithData:mData encoding:NSUTF8StringEncoding];      NSLog(@"response body%@", responseString); }       

   connectionWithRequest需要delegate參數，通過一個delegate來做資料的下載下傳以及Request的接受以及連接配接狀态，此處delegate:self，是以需要本類實作一些方法，并且定義mData做資料的接受。

需要實作的方法：

1、擷取傳回狀态、標頭資訊。

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

2、連接配接失敗，包含失敗。

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

3、接收資料

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

4、資料接收完畢

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

    connectionWithRequest使用起來比較繁瑣，而iOS5.0之前用不支援sendAsynchronousRequest。有網友提出了AEURLConnection解決方案。

AEURLConnection is a simple reimplementation of the API for use on iOS 4. Used properly, it is also guaranteed to be safe against The Deallocation Problem, a thorny threading issue that affects most other networking libraries.      

2、同步請求

同步請求資料方法如下：

- (void)httpSynchronousRequest{          NSURLRequest * urlRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]];     NSURLResponse * response = nil;     NSError * error = nil;     NSData * data = [NSURLConnection sendSynchronousRequest:urlRequest                                           returningResponse:&response                                                       error:&error];          if (error == nil)     {         // 處理資料     } }      

同步請求資料會造成主線程阻塞，通常在請求大資料或網絡不暢時不建議使用。

        從上面的代碼可以看出，不管同步請求還是異步請求，建立通信的步驟基本是一樣的：

         1、建立NSURL

         2、建立Request對象

         3、建立NSURLConnection連接配接。

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參考：

http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLConnection.html#//apple_ref/doc/uid/20001836-BAJEAIEE

http://codewithchris.com/tutorial-how-to-use-ios-nsurlconnection-by-example/

http://kelp.phate.org/2011/06/ios-stringwithcontentsofurlnsurlconnect.html