NSURLConnection异步请求

NSURLConnection异步请求

对于NSURLConnection在5.0后有两种方法实现异步请求，一种是5.0以后引入的+sendAsynchronousRequest:queue:completionHandler:，还有就是2.0就存在的+connectionWithRequest: delegate:。前一种方法当然是最方便的，而且文档全。但是考虑到兼容的问题，往往还是会采用后者，但是问题在于文档的不全，会让人引起混乱，尽管有一个例子SimpleURLConnection的例子。

+sendAsynchronousRequest:queue:completionHandler:

- (void)loadDataSource {    NSString *URLPath = [NSString stringWithFormat:@"http://imgur.com/gallery.json"];    NSURL *URL = [NSURL URLWithString:URLPath];    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL];    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {       NSInteger responseCode = [(NSHTTPURLResponse *)response statusCode];       if (!error && responseCode == 200) {          id res = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];          if (res && [res isKindOfClass:[NSDictionary class]]) {             self.items = [res objectForKey:@"gallery"];             [self dataSourceDidLoad];          } else {             [self dataSourceDidError];          }       } else {          [self dataSourceDidError];       }    }];}

+connectionWithRequest: delegate:

- (void)loadDataSource {    NSString *URLPath = [NSString stringWithFormat:@"http://imgur.com/gallery.json"];    NSURL *URL = [NSURL URLWithString:URLPath];    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL];       [NSURLConnection connectionWithRequest:request delegate:self];}//---------------------------------------// You have to implement below four methods//---------------------------------------- (void)connection:(NSURLConnection *)theConnection didReceiveResponse:(NSURLResponse *)response{    NSInteger responseCode = [(NSHTTPURLResponse *)response statusCode];    _connectedSuccess = responseCode == 200;    NSLog(@"response length=%lld", [response expectedContentLength]);}- (void)connection:(NSURLConnection *)theConnection didReceiveData:(NSData *)data// A delegate method called by the NSURLConnection as data arrives.  The // response data for a POST is only for useful for debugging purposes, // so we just drop it on the floor.{    if (_galleryData == nil) {        _galleryData = [[NSMutableData alloc] initWithData:data];    } else {        [_galleryData appendData:data];    }}- (void)connection:(NSURLConnection *)theConnection didFailWithError:(NSError *)error// A delegate method called by the NSURLConnection if the connection fails. // We shut down the connection and display the failure.  Production quality code // would either display or log the actual error.{}- (void)connectionDidFinishLoading:(NSURLConnection *)theConnection// A delegate method called by the NSURLConnection when the connection has been // done successfully.  We shut down the connection with a nil status, which // causes the image to be displayed.{    if (_connectedSuccess) {        id res = [NSJSONSerialization JSONObjectWithData:_galleryData options:NSJSONReadingMutableContainers error:nil];        if (res && [res isKindOfClass:[NSDictionary class]]) {            self.items = [res objectForKey:@"gallery"];            [self dataSourceDidLoad];        } else {            [self dataSourceDidError];        }        [_galleryData release];        _galleryData = nil;    } else {        [self dataSourceDidError];    }}

实际上必须要实现NSURLConnectionDataDelegate,而这个Protocol的声明在文档中是不容易找到的，只有在这里提到了一下，在SimpleURLConnection中则没有说清楚。不过估计在5.0以前应该是没有这个Protocol的，所以在实现的过程中只要增加这四个方法就可以了，也可以有选择性地增加你想要地因为都是可选地方法。注意在这个代码里面用到了NSJSONSerialization，这个也是5.0引入的，所以要想用JSON Parser可以考虑JSONKit。