Question

下面的代码是一个与URL的连接，并获取一些标头响应，如http代码响应和最终URL（用于重定向的情况）：


- (NSString *)test
{
    __block NSString *cod = @"x";
    NSString *urlString = @"http://www.google.com";
    NSURL *url = [NSURL URLWithString:urlString];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url
                                                           cachePolicy:NSURLRequestReloadIgnoringCacheData
                                                       timeoutInterval:15.0f];

[request setHTTPMethod:@"HEAD"];

[NSURLConnection sendAsynchronousRequest:request
                                   queue:[NSOperationQueue mainQueue]
                       completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
                           NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
                           NSURL *resolvedURL = [httpResponse URL];
                           NSString *code = [NSString stringWithFormat:@"%ld", (long)[httpResponse statusCode]];
                           NSLog(@"%@", resolvedURL);
                           NSLog(@"%@", code);

                           cod = @"y"; // the idea was use something like 'cod = code', then return 'code' at end.. But it dont works too.
                       }];
return cod; }

可以看出，我已将cod变量声明为[request setHTTPMethod:@"HEAD"]; [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) { NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response; NSURL *resolvedURL = [httpResponse URL]; NSString *code = [NSString stringWithFormat:@"%ld", (long)[httpResponse statusCode]]; NSLog(@"%@", resolvedURL); NSLog(@"%@", code); cod = @"y"; // the idea was use something like 'cod = code', then return 'code' at end.. But it dont works too. }]; return cod; }类型并设置为x值。在内部块中，我将cod设置为y值，但在方法结束时，我得到了鳕鱼的x值。我试图使用像cod = code然后返回cod，尊重对象类型，但我在块内分配的任何东西，我都无法获得它之外的值。我做错了什么？

Answer 1

查看方法名称：

[NSURLConnection sendAsynchronousRequest:...

糟糕！所以它是异步的。调用完成块时，您的test方法已经返回。您无法从同步方法返回异步调用的结果，因为它没有意义。使您的课程与网络操作的异步性质保持一致，使用回调，委托等等。总而言之，重新设计您的代码。

返回块外的变量值 - Objective-C，iOS

1 个答案: