從請求中獲取資料到主執行緒

我對 Objective C 和移動開發非常陌生。我想在此會話之外執行獲取并使用回應，誰能告訴我該怎么做？

現在我收到錯誤“使用未宣告的識別符號'用戶名'

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:[NSURL URLWithString:url]];
[request setHTTPMethod:@"GET"];NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

[[session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
    NSString *requestReply = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
    
    NSRange rangeUsername = [requestReply rangeOfString:@"<username>"];
    NSString *username = [requestReply substringFromIndex:rangeUsername.location];
    username = [username stringByReplacingOccurrencesOfString:@"<username>" withString:@""];
    username = [username stringByReplacingOccurrencesOfString:@"</username>" withString:@""];
    
    NSRange rangeDomain = [requestReply rangeOfString:@"<SIP_domain>"];
    NSString *domain = [requestReply substringFromIndex:rangeDomain.location];
    domain = [domain stringByReplacingOccurrencesOfString:@"<SIP_domain>" withString:@""];
    domain = [domain stringByReplacingOccurrencesOfString:@"</SIP_domain>" withString:@""];
}] resume];

NSLog(@"Username: %@", username);
NSLog(@"Domain: %@", domain);

uj5u.com熱心網友回復：

該dataTaskWithRequest方法異步運行，即稍后運行。您不能只參考塊之外的變數。

典型的解決方案是為執行此請求的方法提供一個塊引數，一個完成處理程式，并在dataTaskWithRequest.

例如，您可能有：

- (void)performRequestWithURL:(NSURL *)url completion:(void (^ _Nonnull)(NSString *username, NSString *domain, NSError *error))completion {
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

    NSURLSession *session = [NSURLSession sharedSession];

    [[session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        if (error) {
            dispatch_async(dispatch_get_main_queue(), ^{
                completion(nil, nil, error);
            });
            return;
        }

        NSString *requestReply = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

        NSRange rangeUsername = [requestReply rangeOfString:@"<username>"];
        NSString *username = [requestReply substringFromIndex:rangeUsername.location];
        username = [username stringByReplacingOccurrencesOfString:@"<username>" withString:@""];
        username = [username stringByReplacingOccurrencesOfString:@"</username>" withString:@""];

        NSRange rangeDomain = [requestReply rangeOfString:@"<SIP_domain>"];
        NSString *domain = [requestReply substringFromIndex:rangeDomain.location];
        domain = [domain stringByReplacingOccurrencesOfString:@"<SIP_domain>" withString:@""];
        domain = [domain stringByReplacingOccurrencesOfString:@"</SIP_domain>" withString:@""];

        dispatch_async(dispatch_get_main_queue(), ^{
            completion(username, domain, nil);
        });
    }] resume];
}

并這樣稱呼它：

[self performRequestWithURL:url completion:^(NSString *username, NSString *domain, NSError *error) {
    if (error) {
        NSLog(@"error = %@", error);
        return;
    }

    // use `username` and `domain` here ...
}];

// ... but not here, because the above runs asynchronously

標籤：IOS 目标-c

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