在 onCreateView 之外使用 findViewById 返回 null

Question

我尝试了几种不同的方法，但似乎不起作用。 如果我使用getActivity()或getView()在onCreateView之外执行findViewById ，它会返回 null 并且我的应用程序崩溃。

这是一个代码片段：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View RootView = inflater.inflate(R.layout.fragment_weather, container, false);

    addressTxt = RootView.findViewById(R.id.address);
    updated_atTxt = RootView.findViewById(R.id.updated_at);
    statusTxt = RootView.findViewById(R.id.status);
    tempTxt = RootView.findViewById(R.id.temp);
    temp_minTxt = RootView.findViewById(R.id.temp_min);
    temp_maxTxt = RootView.findViewById(R.id.temp_max);
    sunriseTxt = RootView.findViewById(R.id.sunrise);
    sunsetTxt = RootView.findViewById(R.id.sunset);
    windTxt = RootView.findViewById(R.id.wind);
    pressureTxt = RootView.findViewById(R.id.pressure);
    humidityTxt = RootView.findViewById(R.id.humidity);

    new weatherTask().execute();

    return RootView;
}

class weatherTask extends AsyncTask<String, Void, String> {

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

        getView().findViewById(R.id.loader).setVisibility(View.VISIBLE);
        getView().findViewById(R.id.mainContainer).setVisibility(View.GONE);
        getView().findViewById(R.id.errorText).setVisibility(View.GONE);

    }
}

在这里您可以看到onCreateView下面的方法中的视图正在使用getView() ，但这不起作用。 我如何才能像这样在onCreate之外使用findViewById ？

Answer 1

尝试这个;

TextView addressTxt, updated_atTxt, statusTxt, tempTxt, temp_minTxt,
        temp_maxTxt, sunriseTxt, sunsetTxt, windTxt, pressureTxt, humidityTxt;

//Create your views you used in AsyncTask here
//View YourView, YourContainer, ErrorText


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

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    defineViews(view);
}

private void defineViews(View view){
    addressTxt = view.findViewById(R.id.address);
    updated_atTxt = view.findViewById(R.id.updated_at);
    statusTxt = view.findViewById(R.id.status);
    tempTxt = view.findViewById(R.id.temp);
    temp_minTxt = view.findViewById(R.id.temp_min);
    temp_maxTxt = view.findViewById(R.id.temp_max);
    sunriseTxt = view.findViewById(R.id.sunrise);
    sunsetTxt = view.findViewById(R.id.sunset);
    windTxt = view.findViewById(R.id.wind);
    pressureTxt = view.findViewById(R.id.pressure);
    humidityTxt = view.findViewById(R.id.humidity);

    /*Define your views here
    YourView = view.findViewById(R.id.loader);
    YourContainer = ...
    ErrorText = ...
    ...
    */
}

class weatherTask extends AsyncTask<String, Void, String> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        //YourView.setVisibility(View.VISIBLE);
        //YourContainer.setVisibility(View.GONE);
        //ErrorText.setVisibility(View.GONE);
    }

    @Override
    protected String doInBackground(String... strings) {
        return null;
    }
}

希望这有效。

Answer 2

尝试将您的视图保持为全局并在课堂内的任何地方使用

private View mView;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    mView = inflater.inflate(R.layout.fragment_weather, container, false);


    ....

    return mView;
}

class weatherTask extends AsyncTask<String, Void, String> {

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

        // Use mView here

    }
}

但不推荐，你应该在Activity/Fragment内部初始化视图并将引用传递给AsyncTask