iOS下的网络通信

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HTTP定义了一种在服务器和客户端之间传递数据的途径。

URL定义了一种唯一标示资源在网络中位置的途径。

REQUESTS 和 RESPONSES：

客户端先建立一个TCP连接，然后发送一个请求。服务器受到请求处理后发送一个响应向客户端传递数据。然后客户端可以继续发送请求或者关闭这个TCP连接。

HTTPS：
在TCP连接建立后，发送请求之前，需要建立一个一个SSL会话。

request方法和它们的用途

注意：想server发送大量数据需要用POST，因为GET仅支持发送少量数据（8KB）。

iOS的NSURLRequest和它的子类NSMutableURLRequest提供了建立HTTP请求的方法。

NSURLResponse 和它的子类NSHTTPURLResponse 处理返回的数据。

URL：

Protocol包括HTTP、FTP和file。

URL编码：

NSString *urlString = @"http://myhost.com?query=This is a question"; NSString *encoded = [urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSURL用来管理URL。

IOS HTTP APIS：

涉及到下面一些类：

NSURL, NSURLRequest, NSURLConnection, 和 NSURLResponse.

1、NSURL

NSURL可以定义本地文件和网络文件

NSURL *url = [NSURL urlWithString:@"http://www.google.com"];

NSData *data = [NSData dataWithContentsOfURL:url];

NSURL定义了很多访问器：

if (url.port == nil) { 　　NSLog(@"Port is nil");} else {　　NSLog(@"Port is not nil");}

2、NSURLRequest

创建了NSURL后，就可以用NSURLRequest建立请求了：

NSURL *url = [NSURL URLWithString: @"https://gdata.youtube.com/feeds/api/standardfeeds/top_rated"];if (url == nil) {     NSLog(@"Invalid URL"); 　　 return;}NSURLRequest *request = [NSURLRequest requestWithURL:url]; if (request == nil) {　　NSLog(@"Invalid Request");    return; }

NSMutableURLRequest是NSURLRequest 的子类，提供了改变请求的属性的方法：

NSURL *url = [NSURL urlWithString@"http://server.com/postme"]; NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url]; [req setHTTPMethod:@"POST"];[req setHTTPBody:[@"Post body" dataUsingEncoding:NSUTF8StringEncoding]];

如果你要发送一个图片或者视频，那么用需要用NSInputStream，它没有把数据全部加在到内存。

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];NSInputStream *inStream = [NSInputStream inputStreamWithFileAtPath:srcFilePath];[request setHTTPBodyStream:inStream];[request setHTTPMethod:@"POST"];

3、NSURLResponse

4、NSURLConnection

提供了初始化、开始、和取消一个连接。

发送同步请求：

- (NSArray *) doSyncRequest:(NSString *)urlString {    // make the NSURL object from the string    NSURL *url = [NSURL URLWithString:urlString];        // Create the request object with a 30 second timeout and a cache policy to always retrieve the    // feed regardless of cachability.    NSURLRequest *request =        [NSURLRequest requestWithURL:url                         cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData                     timeoutInterval:30.0];        // Send the request and wait for a response    NSHTTPURLResponse   *response;    NSError             *error;    NSData *data = [NSURLConnection sendSynchronousRequest:request                                          returningResponse:&response                                                      error:&error];    // check for an error    if (error != nil) {        NSLog(@"Error on load = %@", [error localizedDescription]);        return nil;    }        // check the HTTP status    if ([response isKindOfClass:[NSHTTPURLResponse class]]) {        NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;        if (httpResponse.statusCode != 200) {            return nil;        }        NSLog(@"Headers: %@", [httpResponse allHeaderFields]);    }        // Parse the data returned into an NSDictionary    NSDictionary *dictionary =         [XMLReader dictionaryForXMLData:data                                   error:&error];    // Dump the dictionary to the log file    NSLog(@"feed = %@", dictionary);        NSArray *entries =[self getEntriesArray:dictionary];        // return the list if items from the feed.    return entries;}

Queued Asynchronous Requests：

- (void) doQueuedRequest:(NSString *)urlString  delegate:(id)delegate {    // make the NSURL object    NSURL *url = [NSURL URLWithString:urlString];        // create the request object with a no cache policy and a 30 second timeout.    NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:30.0];        // If the queue doesn't exist, create one.    if (queue == nil) {        queue = [[NSOperationQueue alloc] init];    }        // send the request and specify the code to execute when the request completes or fails.    [NSURLConnection sendAsynchronousRequest:request                                        queue:queue                            completionHandler:^(NSURLResponse *response,                                                NSData *data,                                                NSError *error) {                                           if (error != nil) {               NSLog(@"Error on load = %@", [error localizedDescription]);            } else {                                // check the HTTP status                if ([response isKindOfClass:[NSHTTPURLResponse class]]) {                    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;                    if (httpResponse.statusCode != 200) {                        return;                    }                    NSLog(@"Headers: %@", [httpResponse allHeaderFields]);                }                                               // parse the results and make a dictionary                NSDictionary *dictionary =                    [XMLReader dictionaryForXMLData:data                                              error:&error];                NSLog(@"feed = %@", dictionary);                // get the dictionary entries.                NSArray *entries =[self getEntriesArray:dictionary];                // call the delegate                if ([delegate respondsToSelector:@selector(setVideos:)]) {                    [delegate performSelectorOnMainThread:@selector(setVideos:)                                                withObject:entries                                             waitUntilDone:YES];                }            }    }];}

NSURLConnection start方法和Delegate：

GET：

　NSURL  *url=[[ NSURL   alloc ] initWithString :urlString];     NSMutableURLRequest  *request=[[NSMutableURLRequest  alloc ] init ];     NSURLConnection  *connection = [[ NSURLConnection   alloc ]  initWithRequest :request delegate : self ];     if (connection)     {             [connection start];         }     else     {             NSLog ( @"sorry" );     }/** NSURLConnectionDataDelegate*/- (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse *)response{　　[activityIndicator startAnimating]; //UIActivityIndicatorView    NSLog(@"Did Receive Response %@", response);    responseData = [[NSMutableData alloc]init];}- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data{    //NSLog(@"Did Receive Data %@", data);    [responseData appendData:data]; //NSMutableData}- (void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error{    NSLog(@"Did Fail");}- (void)connectionDidFinishLoading:(NSURLConnection *)connection{

[activityIndicator stopAnimating];

    NSLog(@"Did Finish");    // Do something with responseData}

POST：

//initialize new mutable data    NSMutableData *data = [[NSMutableData alloc] init];    self.receivedData = data;        //initialize url that is going to be fetched.    NSURL *url = [NSURL URLWithString:@"http://www.snee.com/xml/crud/posttest.cgi"];        //initialize a request from url    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[url standardizedURL]];        //set http method    [request setHTTPMethod:@"POST"];    //initialize a post data    NSString *postData = [[NSString alloc] initWithString:@"fname=example&lname=example"];    //set request content type we MUST set this value.        [request setValue:@"application/x-www-form-urlencoded; charset=utf-8" forHTTPHeaderField:@"Content-Type"];        //set post data of request    [request setHTTPBody:[postData dataUsingEncoding:NSUTF8StringEncoding]];        //initialize a connection from request    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];    self.connection = connection;    //start the connection    [connection start];

异步请求：
异步请求需要一个run loop来操作代理对象，GCD和NSOperationQueue默认并没有run loop，所以如果你想在后台发起一个HTTP请求，必须确保有run loop。

NSURLConnection connection = [[NSURLConnection alloc] initWithRequest:requestdelegate:self startImmediately:NO];[connection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];[connection start];

上面的代码是在主线程运行，如果想在其他线程运行，可以在其他线程新建一个run loop，并绑定到connection。

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