NSURLConnection使用
通过NSURLConnection进行异步下载
NSURLConnection 提供了两种方式来实现连接,一种是同步的还有一种是异步的,异步的连接将会创建一个新的线程,这个线程将会来负责下载的动作。而对于同步连接,在下载连接和处理通讯时,则会堵塞当前调用线程。
很多开发人员都会觉得同步的连接将会阻塞主线程,其实这样的观点是错误的。一个同步的连接是会阻塞调用它的线程。假设你在主线程中创建一个同步连接,没错,主线程会阻塞。可是假设你并非从主线程开启的一个同步的连接,它将会类似异步的连接一样。因此这样的情况并不会阻塞你的主线程。
其实,同步和异步的主要差别就是执行 runtime 为会异步连接创建一个线程,而同步连接则不会。
//asynchronousRequest connection -(void)fetchAppleHtml{ NSString *urlString = @"http://www.apple.com"; NSURL *url = [NSURL URLWithString:urlString]; // NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url]; NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:30.0f]; //maximal timeout is 30s NSOperationQueue *queue = [[NSOperationQueue alloc] init]; [NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) { if ([data length] > 0 && connectionError == nil) { NSString *documentsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]; NSString *filePath = [documentsDir stringByAppendingPathComponent:@"apple.html"]; [data writeToFile:filePath atomically:YES]; NSLog(@"Successfully saved the file to %@",filePath); NSString *html = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]; NSLog(@"HTML = %@",html); }else if ([data length] == 0 && connectionError == nil){ NSLog(@"Nothing was downloaded."); }else if (connectionError != nil){ NSLog(@"Error happened = %@",connectionError); } }]; }
通过NSURLConnection进行同步下载
使用 NSURLConnection 的 sendSynchronousRequest:returningResponse:error:类方法,我们能够进行同步请求。
在创建一个同步的网络连接的时候我们须要明确一点,并非是我们的这个同步连接一定会阻塞我们的主线程,假设这个同步的连接是创建在主线程上的,那么这样的情况下是会阻塞我们的主线程的,其它的情况下是不一定会阻塞我们的主线程的。假设你在 GCD 的全局并发队列上初始化了一个同步的连接,你事实上并不会阻塞我们的主线程的。
我们来初始化第一个同步连接,并看看会发生什么。在实例中,我们将尝试获取 Yahoo!美国网站主页内容:
//synchronousRequest connection -(void)fetchYahooData{ NSLog(@"We are here..."); NSString *urlString = @"http://www.yahoo.com"; NSURL *url = [NSURL URLWithString:urlString]; NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url]; NSURLResponse *response = nil; NSError *error = nil; NSLog(@"Firing synchronous url connection..."); NSData *data = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error]; 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 return."); }else if (error != nil){ NSLog(@"Error happened = %@",error); } NSLog(@"We are done."); } /* | | as we know, it will chock main thread when we call sendSynchronousRequest on main thread,,,,change below | v */ //call sendSynchronousRequest on GCD pool -(void)fetchYahooData2_GCD{ NSLog(@"We are here..."); NSString *urlString = @"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, ^{ NSURL *url = [NSURL URLWithString:urlString]; NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url]; NSURLResponse *response = nil; NSError *error = nil; NSData *data = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error]; 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); } }); NSLog(@"We are done."); }
查看执行输出结果。分别为:
synchronous download on main thread without GCD
synchronous download on main thread with GCD
能够看到在主线程上调用同步下载会堵塞当前线程,而使用GCD则不会。
通过NSURLConnection发送一个HTTP GET请求
//send a GET request to server with some params -(void)httpGetWithParams{ NSString *urlString = @"http://chaoyuan.sinaapp.com"; urlString = [urlString stringByAppendingString:@"?p=1059"]; NSURL *url = [NSURL URLWithString:urlString]; NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url]; [urlRequest setTimeoutInterval:30.0f]; [urlRequest setHTTPMethod:@"GET"]; NSOperationQueue *queue = [[NSOperationQueue alloc] init]; [NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) { if ([data length] > 0 && connectionError == nil) { NSString *html = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]; NSLog(@"HTML = %@",html); }else if([data length] == 0 && connectionError == nil){ NSLog(@"nothing was download."); }else if(connectionError != nil){ NSLog(@"Error happened = %@",connectionError); } }]; }
通过NSURLConnection发送一个HTTP POST请求
//send a POST request to a server with some params -(void)httpPostWithParams{ NSString *urlAsString = @"http://chaoyuan.sinaapp.com"; urlAsString = [urlAsString stringByAppendingString:@"?param1=First"]; urlAsString = [urlAsString stringByAppendingString:@"¶m2=Second"]; NSURL *url = [NSURL URLWithString:urlAsString]; NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url]; [urlRequest setTimeoutInterval:30.0f]; [urlRequest setHTTPMethod:@"POST"]; 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); } }]; }
tips:
except http get and post there are http delete and put and something else, if you are crazy about http, please GOOGLE!
完整项目代码在这里。
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