ios - 如何使用异步 NSURLConnection 将数据传递给 View Controller

Question

我有 View Controller，我可以从 Web 获取数据，解析 Json，并将字符串传递给另一个 View Controller。如果我使用同步 NSURLConnection，一切正常。

但是如果我切换到异步，那么方法 (void)prepareForSegue:(UIStoryboardSegue *) 在解析我从 web 获取的 Json 数据之前调用。

直接跳过_jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil]方法。有什么想法吗？预先感谢您的帮助。这是我的代码:

-(void)getClothInfo {
    NSString *allowedClothSizeToServer = [_foreignSizeToServer     stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
    NSString *getDataURL = [NSString stringWithFormat:@"http://xsdcompany.com/jsoncloth.php?foreignSize=%@",allowedClothSizeToServer];
    NSURL *url = [NSURL URLWithString:getDataURL];

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPMethod:@"GET"];

    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler: ^(NSURLResponse *response, NSData *data, NSError *connectionError) {

        if (connectionError) {
            [self showAlertWithMessage2:@"Server is Unavialable"];
        } else {
            _jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];

            //Loop trough our jsonArray
            for (int i=0; i<_jsonArray.count; i++) {
                //Create our size object
                _usSizeFromServer = [[_jsonArray objectAtIndex:i] objectForKey:@"usSizeCloth"];
            }
        }
    }];
}

- (IBAction)getIt:(id)sender {
    // Validate data
    if ([self validData] == NO)
    {
         return;
    }

    [self getClothInfo];
    [self showNextViewController];
}

-(void) showNextViewController {
    [self performSegueWithIdentifier:@"GetCLothInfo" sender:nil];
}

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    ResultViewController *resultViewController = [segue destinationViewController];
    resultViewController.foreignSizeToResult = [[NSString alloc] initWithFormat:@"%@ size for %@ is %@", [_pickerProcessor selectedCountry].countryName, [_pickerProcessor selectedCloth].clothName, [_pickerProcessor selectedSize].sizeName];
    resultViewController.dataForUsSize = [[NSString alloc] initWithFormat:@"Your US size for %@ is %@", [_pickerProcessor selectedCloth].clothName, _usSizeFromServer];
}

Answer 1

您有两个选择。您可以从 getClothInfo 方法内的完成 block 调用 showNextViewController。或者更好的是，将完成 block 参数添加到您的 getClothInfo 方法，并从 NSURLConnection 的完成 block 中调用它。

像这样:

-(void)getClothInfo:(void ^(void))completion {
    NSString *allowedClothSizeToServer = [_foreignSizeToServer     stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
    NSString *getDataURL = [NSString stringWithFormat:@"http://xsdcompany.com/jsoncloth.php?foreignSize=%@",allowedClothSizeToServer];
    NSURL *url = [NSURL URLWithString:getDataURL];

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPMethod:@"GET"];

    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler: ^(NSURLResponse *response, NSData *data, NSError *connectionError) {

        if (connectionError) {
            [self showAlertWithMessage2:@"Server is Unavialable"];
        } else {
            _jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];

            //Loop trough our jsonArray
            for (int i=0; i<_jsonArray.count; i++) {
                //Create our size object
                _usSizeFromServer = [[_jsonArray objectAtIndex:i] objectForKey:@"usSizeCloth"];
            }

            if (completion) {
                dispatch_async(dispatch_get_main_queue(), ^{
                     completion();
                });
            }
        }
    }];
}

- (IBAction)getIt:(id)sender {
    // Validate data
    if ([self validData] == NO)
    {
         return;
    }

    [self getClothInfo:^ {
        [self showNextViewController];
    }];
}