iOS網絡通信http之NSURLConnection

文章來源：http://blog.csdn.net/xyz_lmn/article/details/8968182

 移動互聯網時代，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，增強客戶端與服務器交互。這一篇提供了使用NSURLConnection實現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，從而使iOS5支持兩種異步請求方式。我們先從新增類開始。

1）sendAsynchronousRequest

iOS5.0開始支持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就開始支持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來做數據的下載以及Request的接受以及連接狀態，此處delegate:self，所以需要本類實現一些方法，並且定義mData做數據的接受。

需要實現的方法：

1、獲取返回狀態、包頭信息。

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

2、連接失敗，包含失敗。

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

3、接收數據

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

4、數據接收完畢

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

    connectionWithRequest使用起來比較繁瑣，而iOS5.0之前用不支持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

同步請求數據方法如下：

- (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)
    {
        // 處理數據
    }
}

同步請求數據會造成主線程阻塞，通常在請求大數據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、創建NSURL

         2、創建Request對象

         3、創建NSURLConnection連接。

         NSURLConnection創建成功後，就創建了一個http連接。異步請求和同步請求的區別是：創建了異步請求，用戶可以做其他的操作，請求會在另一個線程執行，通信結果及過程會在回調函數中執行。同步請求則不同，需要請求結束用戶才能做其他的操作。

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* @author 張興業

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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