设置请求头：[manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
GET方法设置请求头的时候没什么问题；
但是使用POST方法时设置无效，使用其他方法都没用，后来发现没有序列化
manager.requestSerializer = [AFJSONRequestSerializer serializer];
注意： 和manager.requestSerializer = [AFHTTPRequestSerializer serializer];不一样
AFHTTPSessionManager *manager = [[AFHTTPSessionManager alloc]initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
manager.requestSerializer = [AFJSONRequestSerializer serializer];
[manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
[manager POST:url parameters:parametersDictionary progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"success!");
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"error: %@", error);
}];
参考：
https://www.jianshu.com/p/cd53b108dd42
https://www.jianshu.com/p/625924f6f052
原文：https://www.cnblogs.com/lulushen/p/9762025.html