Iphone用http协议和服务器通信有两种方式，一种是同步一种是异步的，所谓同步是指当客户端调用post/get的方式的函数向服务器发出数据请求后，该函数不会直接返回，只有得到服务器响应或者请求时间timeout之后才会返回继续执行其它任务。异步采用回调的方式，即请求发送后，函数会立即返回，一旦服务器联结成功操作系统会去触发相应的回调进行相应的处理。这和window的消息处理机制一样。
同步一般用于一次性操作，如判断当前网络是否可用等等。多的就不再一一介绍，在实现上面有两点不同:
(1)在用NSURLConnect的时候一个调用同步函数一个调用了异步函数。
(2)异步的需要实现delegate的相关回调函数。
以下是参考代码：
同步方式：
-(void)UpadaPost:(NSString *)strcontext URL:(NSString *)urlstr{
NSLog(urlstr);
NSLog(strcontext);
assert(strcontext != NULL);
assert(urlstr != NULL);
NSData*postData=[strcontextdataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
NSString *postLength = [NSString stringWithFormat:@"%d", [postData length]];
NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];
[request setURL:[NSURL URLWithString:urlstr]];
[request setHTTPMethod:@"POST"]; [request setTimeoutInterval: 20];//setting timeout
[request setValue:postLength forHTTPHeaderField:@"Content-Length"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setHTTPBody:postData];
NSURLResponse *respone;
NSError *error;
NSData*myReturn=[NSURLConnection sendSynchronousRequest:request returningResponse:&respone
error:error];
NSLog(@"%@", [[NSString alloc] initWithData:myReturn encoding:NSUTF8StringEncoding]);
}
异步方式：
-(void)UpadaPost:(NSString *)strcontext URL:(NSString *)urlstr{
NSLog(urlstr);
NSLog(strcontext);
assert(strcontext != NULL);
assert(urlstr != NULL);
NSData *postData = [strcontext dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
NSString *postLength = [NSString stringWithFormat:@"%d", [postData length]];
NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];
[request setURL:[NSURL URLWithString:urlstr]];
[request setHTTPMethod:@"POST"]; [request setTimeoutInterval: 20];//setting timeout
[request setValue:postLength forHTTPHeaderField:@"Content-Length"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setHTTPBody:postData];
NSURLConnection *conn=[[NSURLConnection alloc] initWithRequest:request delegate:self];
if (conn)
{
NSLog(@"Connection success");
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
[conn retain];
}
else
{
// inform the user that the download could not be made
}
}
#pargma mark------------------以下为相应的回调函数-------------------------------
// 收到响应时, 会触发
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
// 注意这里将NSURLResponse对象转换成NSHTTPURLResponse对象才能去
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
if ([response respondsToSelector:@selector(allHeaderFields)]) {
NSDictionary *dictionary = [httpResponse allHeaderFields];
NSLog([dictionary description]);
NSLog(@"%d",[response statusCode]);
}
}
//链接错误
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
//[self performSelectorOnMainThread:@selector(httpConnectEnd) withObject:nil waitUntilDone:NO];
NSLog(@"%@",[error localizedDescription]);
}
// Called when a chunk of data has been downloaded.
//接收数据 每收到一次数据, 会调用一次
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
// Process the downloaded chunk of data.
NSLog(@"%d", [data length]);
//NSLog(@"%@", [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);
//[self performSelectorOnMainThread:@selector(updateProgress) withObject:nil waitUntilDone:NO];
}
//接收结束
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(@"%@",connection);
//NSLog(@"%lld", received_);
//[self performSelectorOnMainThread:@selector(httpConnectEnd) withObject:nil waitUntilDone:NO];
// Set the condition which ends the run loop.
}
[提示]:
According to a post on the Apple developer forum, the minimum timeout interval for POST is 240 seconds. Any timeout interval shorter than that is ignored.
If you require a shorter timeout interval, use an async request along with a timer and call cancel on the NSURLConnection as needed.