93.AFNetworking manager.requestSerializer.timeoutInterval无效问题 超时无效问题

// 设置超时时间
    [manager.requestSerializerwillChangeValueForKey:@"timeoutInterval"];
    manager.requestSerializer.timeoutInterval =10.f;
    [manager.requestSerializerdidChangeValueForKey:@"timeoutInterval"];
 [manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Accept"];
[manager.requestSerializer setValue:@"application/json; charset=utf-8" forHTTPHeaderField:@"Content-Type"];  
会引起AAFnetworking 在3G网络下强制60秒超时
无意中发现代码执行顺序调整后就正常了    找了半天没找到原因   以上代码在Wifi情况下是能保证10秒超时的   真奇葩，不懂原理啊 

 [manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Accept"];
[manager.requestSerializer setValue:@"application/json; charset=utf-8" forHTTPHeaderField:@"Content-Type"];  //这两句会引起超时无效 删除就可以了

    [manager.requestSerializer willChangeValueForKey:@"timeoutInterval"];

    manager.requestSerializer.timeoutInterval = 10.f;

    [manager.requestSerializer didChangeValueForKey:@"timeoutInterval"];