《iOS简单网络传输》iOS7 CookBook系列

如何利用NSURLConnection 来获得网络资源?
引用书中的话
“
     有使用NSURLConnection的两个方法。一个是异步的，而另一个是同步的。异步连接将创建一个新的线程并执行其下载过程在新线程。一个同步连接将阻塞调用线程且同时下载的内容。
     许多开发者认为，一个同步连接阻塞主线程，但是这是不正确的。一个同步连接将始终阻止它被启动的线程。如果你从主线程的启动同步连接，是的，主线程将被阻塞。但是，如果你从一个线程在主线程之外启动同步连接，它会像一个异步连接，它不会阻止你的主线程。
     实际上，同步和异步连接之间的唯一区别在于，运行时<runtime>将为异步连接创建一个线程，而它不会对一个同步连接这样做。

”
异步连接的过程:




     为了创建一个异步连接，我们需要做到以下几点：1。在NSString的实例URL
2。我们的字符串转换为NSURL的一个实例。
    NSString *urlAsString = @"http://www.apple.com";
    NSURL *url = [NSURL URLWithString:urlAsString];





3.我们可以创建一个异步的URL连接

 NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
4.创建一个操作队列
 NSOperationQueue *queue = [[NSOperationQueue alloc] init];
5.把请求赋值给NSURLConnection，开始请求数据
6.请求结束后，在completionHandler闭包里接收  
      A. NSData *data服务器给我们的二进制数据
      B.NSURLResponse *response,它封装了服务器发给我们的信息。
      C.NSError *error失败后的信息


    [NSURLConnection
    sendAsynchronousRequest:urlRequest
    queue:queue
    completionHandler:^(NSURLResponse *response,
                       NSData *data,
                       NSError *error) {
if ([data length] ]]>0 && error == nil){
       NSString *html = [[NSString alloc] initWithData:data
                                              encoding:NSUTF8StringEncoding];
       NSLog(@"HTML = %@", html);
     }
else if ([data length] == 0 && error == nil){
       NSLog(@"Nothing was downloaded.");
     }
else if (error != nil){NSLog(@"Error happened = %@", error);

} }]; 
————————————————————————————————————————-——
##异步连接
1.让我们看看例子,我们尝试异步获取apple网站的HTML内容,然后打印这些内容去命令行窗口,把数据写入html文件

    NSString *urlAsString = @"http://www.apple.com";
    NSURL *url = [NSURL URLWithString:urlAsString];
     NSURLRequest *urlRequest =
        [NSURLRequest
         requestWithURL:url
         cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData
         timeoutInterval:30.0f];
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [NSURLConnection
    sendAsynchronousRequest:urlRequest
    queue:queue
    completionHandler:^(NSURLResponse *response,
                       NSData *data,
                       NSError *error) {
if ([data length] ]]>0 && error == nil){
       NSString *html = [[NSString alloc] initWithData:data
                                              encoding:NSUTF8StringEncoding];
 /* Append the filename to the documents directory */

             NSURL *filePath =
             [[self documentsFolderUrl]

              URLByAppendingPathComponent:@"apple.html"];
             [data writeToURL:filePath atomically:YES];
             NSLog(@"Successfully saved the file to %@", filePath);




     }
else if ([data length] == 0 && error == nil){
       NSLog(@"Nothing was downloaded.");
     }
else if (error != nil){ NSLog(@"Error happened = %@", error);

} }]; 






##同步连接

1.让我们把完全相同的同步连接连接一个  global concurrent queue in GCD,这保证了程序的并发性

 NSLog(@"We are here...");
        NSString *urlAsString = @"http://www.yahoo.com";
        NSLog(@"Firing synchronous url connection...");
dispatch_queue_t dispatchQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(dispatchQueue, ^(void) {
            NSURL *url = [NSURL URLWithString:urlAsString];
            NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
            NSURLResponse *response = nil;
            NSError *error = nil;

NSData *data = [NSURLConnection sendSynchronousRequest:urlRequest
                                     returningResponse:&response
if ([data length] > 0 && error == nil){ NSLog(@"%lu bytes of data was returned.",
(unsigned long)[data length]);
} else if ([data length] == 0 && error == nil){
                NSLog(@"No data was returned.");
            }
else if (error != nil){ NSLog(@"Error happened = %@", error);
} }); 


##GET,POST,PUT,DEL请求


## http://example.com/?param1=value1&param2=value2


 NSString *urlAsString = @“ http://example.com/”;
        urlAsString = [urlAsString stringByAppendingString:@"?param1=First"];
        urlAsString = [urlAsString stringByAppendingString:@"&param2=Second"];
        NSURL *url = [NSURL URLWithString:urlAsString];
        NSMutableURLRequest *urlRequest =
            [NSMutableURLRequest requestWithURL:url];
        [urlRequest setTimeoutInterval:30.0f];
##GET请求
        [urlRequest setHTTPMethod:@"GET"];
##Post请求:提交数据
     [urlRequest setHTTPMethod:@"POST"];
      NSString *body = @"bodyParam1=BodyValue1&bodyParam2=BodyValue2";
        [urlRequest setHTTPBody:[body dataUsingEncoding:NSUTF8StringEncoding]];
##Put请求:更新数据
     [urlRequest setHTTPMethod:@"PUT"];
      NSString *body = @"bodyParam1=BodyValue1&bodyParam2=BodyValue2";
        [urlRequest setHTTPBody:[body dataUsingEncoding:NSUTF8StringEncoding]];
##Del请求:删除数据
          [urlRequest setHTTPMethod:@"DELETE"];
      NSString *body = @"bodyParam1=BodyValue1&bodyParam2=BodyValue2";     
     [urlRequest setHTTPBody:[body dataUsingEncoding:NSUTF8StringEncoding]];
     
     
          NSOperationQueue *queue = [[NSOperationQueue alloc] init];
        [NSURLConnection
         sendAsynchronousRequest:urlRequest
         queue:queue
         completionHandler:^(NSURLResponse *response,
                             NSData *data,
                             NSError *error) {
if ([data length] ]]>0 && error == nil){ NSString *html =
                 [[NSString alloc] initWithData:data
                                       encoding:NSUTF8StringEncoding];
                 NSLog(@"HTML = %@", html);
             }
else if ([data length] == 0 && error == nil){ NSLog(@"Nothing was downloaded.");
} else if (error != nil){
NSLog(@"Error happened = %@", error);
         }
     }];




##把内容简单分享去twitter

if ([SLComposeViewController
isAvailableForServiceType:SLServiceTypeTwitter]){

            SLComposeViewController *controller =
            [SLComposeViewController

             composeViewControllerForServiceType:SLServiceTypeTwitter];

            [controller setInitialText:@"MacBook Airs are amazingly thin!"];
            [controller addImage:[UIImage imageNamed:@"MacBookAir"]];
            [controller addURL:[NSURL URLWithString:@"http://www.apple.com/"]];

            controller.completionHandler = ^(SLComposeViewControllerResult result){
                NSLog(@"Completed");

};

            [self presentViewController:controller animated:YES completion:nil];

}else{
NSLog(@"The twitter service is not available");

}