Question

我正在使用AFNetworking进行一些GET查询。但我的函数总是返回nil值。哪里错了？

+ (NSString *)getRequestFromUrl:(NSString *)requestUrl {
    NSString * completeRequestUrl = [NSString stringWithFormat:@"%@%@", BASE_URL, requestUrl];
    __block NSString * results;
    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    [manager GET:completeRequestUrl parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
        results = [NSString stringWithFormat:@"%@", responseObject];
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        results = [NSString stringWithFormat:@"Error"];
    }];
    NSLog(@"%@", results);
    return results;
}

THX！阿尔乔姆。

Answer 1

您没有看到结果，因为您为success和failure传入的块是异步运行的;当您的NSLog被调用时，Web服务还没有返回。如果您在成功和失败块中移动NSLog，您应该看到结果输出到您的控制台。

由于这些调用的异步性质，您将无法简单地从方法返回值。相反，您可能希望将自己的块作为参数，然后在获得结果时可以调用该参数。例如：

+ (void)getRequestFromUrl:(NSString *)requestUrl withCompletion:((void (^)(NSString *result))completion 
{
    NSString * completeRequestUrl = [NSString stringWithFormat:@"%@%@", BASE_URL, requestUrl];
    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    [manager GET:completeRequestUrl parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
        NSString *results = [NSString stringWithFormat:@"%@", responseObject];
        if (completion)
            completion(results);
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSString *results = [NSString stringWithFormat:@"Error"];
        if (completion)
            completion(results);
    }];
}

然后您可以这样调用您的方法：

[YourClass getRequestFromUrl:@"http://www.example.com" withCompletion:^(NSString *results){
    NSLog(@"Results: %@", results);
}

AFNetworking的示例项目有一个使用块参数从Web服务调用中返回值的示例：https://github.com/AFNetworking/AFNetworking/blob/master/Example/Classes/Models/Post.m

Answer 2

- (void)POST:(NSString *)URLString 
          parameters:(id)parameters
          constructingBodyWithBlock:(void (^)(id <AFMultipartFormData> formData))block
          progress:(nullable void (^)(NSProgress * _Nonnull))uploadProgress
          success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
          failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{

 [_manager POST:[NSString stringWithFormat:@"%@%@",API_HOST,URLString] parameters:parameters constructingBodyWithBlock:^(id<AFMultipartFormData>  _Nonnull formData) {
    block(formData);
 } progress:^(NSProgress * _Nonnull uploadProgress1) {
    uploadProgress(uploadProgress1);
 } success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
    success(task,responseObject);
 } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {

    failure(task,error);
}];
}

始终从iOS中的函数获得nil值

2 个答案: