从 class 扩展 AsyncTask 返回对象时出现问题

Question

我在使用 getter 函数 returning 来自 class HttpRequestCurrentWeather 扩展 AsyncTask 的对象时遇到问题。在此 class 中，我收到来自 API 的数据，并希望根据收到的内容在 CurrentWeatherFragment 中设置一些 TextView。问题是我不能 return 将 DataModel 的整个对象添加到 Fragment 并在那里设置组件，也不能将 TextViews 设置为 onPostExecute() 方法，因为我得到了 NullPointerException（java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法 'android.view.View android.view.View.findViewById(int)'）。我应该如何设置这些 TextView？

public class CurrentWeatherFragment extends Fragment {
    DataModel dataModel = new DataModel();

    TextView tv_city;
    TextView tv_temperature;
    TextView tv_pressure;

    public void setComponents() {
        this.tv_city = getView().findViewById(R.id.tv_current_city_name);
        tv_city.setText(dataModel.getName());

        this.tv_temperature = getView().findViewById(R.id.tv_current_temperature);
        tv_temperature.setText(dataModel.getTemp());

        this.tv_pressure = getView().findViewById(R.id.tv_current_pressure);
        tv_pressure.setText(dataModel.getPressure());
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View RootView = inflater.inflate(R.layout.fragment_current_weather_layout, container, false);


        HttpRequestCurrentWeather httpRequestCurrentWeather1 = new HttpRequestCurrentWeather();
        httpRequestCurrentWeather1.execute("", "", "");

        // here I receive null object, but why?
        dataModel = httpRequestCurrentWeather1.getDataModel();

        // set the texts in components:
        setComponents();

        return RootView;
    }
}

public class HttpRequestCurrentWeather extends AsyncTask<String, Void, DataModel> {
        DataModel dataModel;

        public HttpRequestCurrentWeather() {
            this.dataModel = null;
        }

        @Override
        protected DataModel doInBackground(String... params) {
            ApiCurrentWeather apiCurrentWeather1 = new ApiCurrentWeather("London", "uk");

            try {
                // catch the model with recived data from API:
                dataModel = apiCurrentWeather1.getWeather();
            } catch (IOException e) {
                e.printStackTrace();
            }

            return dataModel;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(DataModel dataModel) {
        super.onPostExecute(dataModel);

        CurrentWeatherFragment fragment = new CurrentWeatherFragment();

        TextView tv_temperature = (TextView)fragment.getView().findViewById(R.id.tv_current_temperature);
        tv_temperature.setText(dataModel.getTemp());

    }

    // this function returns NULL object ????
    public DataModel getDataModel(){
        return this.dataModel;
    }
}

Answer 1

老实说，这不是合适的答案，但我试图使用 AsyncTask 实现的目标似乎使用 Retrofit 更容易，所以我最终放弃了这个想法并决定 改用 Retrofit。如果你有类似的问题，忘记 AsyncTask - Retrofit 更适合这个！

从 class 扩展 AsyncTask 返回对象时出现问题

Problem with returning object form a class extending AsyncTask

java

android

return

android-asynctask

android-fragments