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通过NSURLConnection进行异步下载
NSURLConnection 提供了两种方式来实现连接,一种是同步的另一种是异步的,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,则会阻塞当前调用线程。
许多开发者都会认为同步的连接将会堵塞主线程,其实这种观点是错误的。一个同步的连接是会阻塞调用它的线程。如果你在主线程中创建一个同步连接,没错,主线程会阻塞。但是如果你并不是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。因此这种情况并不会堵塞你的主线程。事实上,同步和异步的主要区别就是运行 runtime 为会异步连接创建一个线程,而同步连接则不会
objc] view plaincopyprint?在CODE上查看代码片派生到我的代码片
//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,我们可以进行同步请求。在创建一个同步的网络连接的时候我们需要明白一点,并不是是我们的这个同步连接一定会堵塞我们的主线程,如果这个同步的连接是创建在主线程上的,那么这种情况下是会堵塞我们的主线程的,其他的情况下是不一定会堵塞我们的主线程的。如果你在 GCD 的全局并发队列上初始化了一个同步的连接,你其实并不会堵塞我们的主线程的。
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!美国站点主页内容:
//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.");
}
查看运行输出结果，分别为：
synchronous download on main thread without GCD
synchronous download on main thread with GCD
可以看到在主线程上调用同步下载会阻塞当前线程，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
[objc] view plaincopyprint?在CODE上查看代码片派生到我的代码片
//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);
}
}];
}
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原文地址：http://www.cnblogs.com/deng37s/p/4600577.html
