java - 从内部类获取变量的值

我有一个在其中实现一个类的方法：

public class RetrofitCallBackUtil {
    private ArrayList<Message> messages = new ArrayList<>();


    public ArrayList<Message> getLastTenMessageCallBack(int user_id, int sender_id, int offset_number, RESTDatabaseDAO service) {
        Call<ArrayList<Message>> call = service.getLastTenMessage(user_id, sender_id, offset_number);

        call.enqueue(new Callback<ArrayList<Message>>() {
            @Override
            public void onResponse(Call<ArrayList<Message>> call, Response<ArrayList<Message>> response) {
                if (response.isSuccess()) {
                    messages = response.body();
                    Log.i("Success", "Good ten " + response.body().size());
                } else {
                    Log.i("Success", "Not good  ten" + response.raw());
                }
            }

            @Override
            public void onFailure(Call<ArrayList<Message>> call, Throwable t) {
                Log.i("Fail", "Failure ten " + t.toString());
            }
        });
        //Still get NullPointException from here. (messages.size())
        Log.i("Success", "Good ten activity" + messages.size());
        return messages;
    }

}

我想获取消息变量的值，但不能。我还创建了一个全局变量List<Message> messages并返回，但仍然无法从response.body()获取值。有人对此有解决方案吗？

更新：

我想要这样的东西：

List<Message>  testMessages = retrofitCallBackUtil.getLastTenMessageCallBack(AppConfig.USER_ID, userId, 0, service);

因为我想多次使用该方法的结果，所以我希望它向我返回数据。

最佳答案

onResponse和onFailure是异步调用的，因此当您尝试return messages;时，尚未对其进行更新。

从回调中返回它。

编辑1：

public void getLastTenMessageCallBack(int user_id, int sender_id, int offset_number, RESTDatabaseDAO service) {
     Call<ArrayList<Message>> call = service.getLastTenMessage(user_id, sender_id, offset_number);
     call.enqueue(new Callback<ArrayList<Message>>() {
          @Override
          public void onResponse(Call<ArrayList<Message>> call, Response<ArrayList<Message>> response) {
               if (response.isSuccess()) {
           // THIS IS BEING CALLED AFTER YOUR METHODS RETURNS, SO UPDATE YOUR VIEWS LIKE THIS.

            updateViews(response.body());
            Log.i("Success", "Good ten " + response.body().size());
        } else {
            Log.i("Success", "Not good  ten" + response.raw());
        }
    }

    @Override
    public void onFailure(Call<ArrayList<Message>> call, Throwable t) {
        Log.i("Fail", "Failure ten " + t.toString());
    }
   });


}
public void updateViews(List<Messages> messages){
    //use messages to update your views here.
}

编辑2：现在，由于您要从许多地方调用它，因此传递诸如requestCode之类的内容，并检查相同的onResponse以识别调用的来源。

public void getLastTenMessageCallBack(final int requestCode, int user_id, ..

和onResponse

updateViews(requestCode, response.body());

并通过比较请求代码相应地更新您的视图。

public void updateViews(int requestCode, List<Messages> messages){
    if(requestCode==XYZ)
    //use messages to update your views here.
}

编辑3：
定义自己的interface以接收回调：

public interface NetworkResponseCallback {
   void onSuccess(ArrayList<Message>> messages);
   void onFailure(); //if you want to pass something else, like cause of failure you can add it.
}

现在，更改您的方法定义：

public void getLastTenMessageCallBack(int user_id, ... , final NetworkResponseCallback networkResponseCallback){

实现onResponse和onFailure：

if (response.isSuccess()) {
  if(networkResponseCallback!=null)
       networkResponseCallback.onSuccess(response.body());


public void onFailure(Call<ArrayList<Message>> call, Throwable t) {
    Log.i("Fail", "Failure ten " + t.toString());
    networkResponseCallback.onFailure();
}

像这样调用getLastTenMessageCallBack方法：

getLastTenMessageCallBack(int user_id, int sender_id, int offset_number, RESTDatabaseDAO service, new NetworkResponseCallback() {
        @Override
        public void onSuccess(List<Messages> messages) {

        }

        @Override
        public void onFailure() {

        }
    });