java - 带复选框的 fragment 中的 NullPointEreException

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 7 年前。

在我的应用程序中，我有一个 fragment ，其中有任何复选框。当我启动 TextToSpech 时。我创建了一个类似的版本，没有 fragment ，并且工作正常。但是当我在 fragment 中实现它时，它不起作用。她是我的代码:

public class OneFragment extends Fragment implements TextToSpeech.OnInitListener, CompoundButton.OnCheckedChangeListener {
private TextToSpeech tts;

ListView listView;
ArrayAdapter<Model> adapter;
List<Model> list = new ArrayList<Model>();

public OneFragment() {
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

}

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

    View returnView = inflater.inflate(R.layout.fragment_one, container, false);
    listView = (ListView) returnView.findViewById(R.id.listView);
    adapter = new MyAdapter(getActivity(), getModel());
    listView.setAdapter(adapter);
    final CheckBox chk = (CheckBox)returnView.findViewById(R.id.checkBox);
    chk.setOnCheckedChangeListener(OneFragment.this);

    return returnView;
}

@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (isVisibleToUser) {
        tts = new TextToSpeech(getActivity(), this);
    }
}

private List<Model> getModel() {
    list.add(new Model("Linux", "S"));
    list.add(new Model("Linux", "S"));
    list.add(new Model("Linux", "S"));
    list.add(new Model("Linux", "S"));
    list.add(new Model("Linux", "S"));

    return list;
}

@Override
public void onInit(int status) {
    if (status == TextToSpeech.SUCCESS) {

        int result = tts.setLanguage(Locale.ITALIAN);

        if (result == TextToSpeech.LANG_MISSING_DATA
                || result == TextToSpeech.LANG_NOT_SUPPORTED) {
            Log.e("TTS", "This Language is not supported");
        } else {

            startSpeak();
        }

    } else {
        Log.e("TTS", "Initilization Failed!");
    }
}

private void startSpeak() {
    tts.speak("Ciao", TextToSpeech.QUEUE_FLUSH, null);
}

@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
    CheckBox chk = (CheckBox)getActivity().findViewById(R.id.checkBox);
      for (Model i: list ) {
        if (chk.isChecked()) {
            this.startSpeak();
        }
    }
}
}

这是部分 LogCat 结果:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.CheckBox.setOnCheckedChangeListener(android.widget.CompoundButton$OnCheckedChangeListener)' on a null object reference

我该怎么办？

Answer 1

i have a fragment were i have any checkbox

如果 CheckBox 位于 R.layout.fragment_one 中的 Fragment 布局内，则使用 OneFragment.this.getView() 从布局访问 CheckBox 而不是 getActivity() :

CheckBox chk = (CheckBox)OneFragment.this.getView().findViewById(R.id.checkBox);

或者将 CheckBox chk 声明为类级别变量并在 onCreateView 内初始化它:

...
chk = (CheckBox)returnView.findViewById(R.id.checkBox);
...