移動網際網路時代，網路通訊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路通訊，增強客戶端與伺服器互動。這一篇提供了使用NSURLConnection實現http通訊的方式。

          NSURLConnection提供了非同步請求、同步請求兩種通訊方式。

1、非同步請求

       iOS5.0 SDK NSURLConnection類新增的sendAsynchronousRequest:queue:completionHandler:方法，從而使iOS5支援兩種非同步請求方式。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 *[email protected]"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);
                               }
                           }];

    
}
 

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引數，通過一個delegate來做資料的下載以及Request的接受以及連線狀態，此處delegate:self，所以需要本類實現一些方法，並且定義mData做資料的接受。

需要實現的方法：

1、獲取返回狀態、包頭資訊。

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

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

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

- (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 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執行緒阻塞，通常在請求大資料或網路不暢時不建議使用。

        從上面的程式碼可以看出，不管同步請求還是非同步請求，建立通訊的步驟基本是一樣的：

         1、建立NSURL

         2、建立Request物件

         3、建立NSURLConnection連線。

         NSURLConnection建立成功後，就建立了一個http連線。非同步請求和同步請求的區別是：建立了非同步請求，使用者可以做其他的操作，請求會在另一個執行緒執行，通訊結果及過程會在回撥函式中執行。同步請求則不同，需要請求結束使用者才能做其他的操作。