[manager.requestSerializer willChangeValueForKey:@"timeoutInterval"];
manager.requestSerializer.timeoutInterval=10.f;
[manager.requestSerializer didChangeValueForKey:@"timeoutInterval"];
[manager.requestSerializer willChangeValueForKey:@"timeoutInterval"];
manager.requestSerializer.timeoutInterval=10.f;
[manager.requestSerializer didChangeValueForKey:@"timeoutInterval"];