Null 傳遞上下文時

Question

在我的對話框中，我有一個可以單擊的按鈕（類： Dialog ）。 單擊該按鈕后，將調用方法customTts() （在MainActivity類中）：

@RequiresApi(api = Build.VERSION_CODES.KITKAT)
public void CustomTts(String input) throws Exception {
    Tts tts = new Tts(MainActivity.this, _mediaPlayer, barTop, barBottom);
    tts.say("Hello!");
}

我得到的錯誤是：

W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference

Tts()的第一個參數需要Context 。 所以看起來MainActivity.this返回null 。

public class Tts extends MainActivity {
    public Context context;
    private final MediaPlayer _mediaPlayer;
    private CopyBarVisualizer _barTop;
    private CopyBarVisualizer _barBottom;

    public Tts(Context context, MediaPlayer _mediaPlayer, BarVisualizer _barTop, BarVisualizer _barBottom) {
        this.context = context;
        this._mediaPlayer = _mediaPlayer;
        this._barTop = (CopyBarVisualizer) _barTop;
        this._barBottom = (CopyBarVisualizer) _barBottom;
    }

    @SuppressLint({"NewApi", "ResourceType", "UseCompatLoadingForColorStateLists"})
    @RequiresApi(api = Build.VERSION_CODES.KITKAT)
    public void say(String text) throws Exception {
        InputStream stream = context.getResources().openRawResource(R.raw.credential); // R.raw.credential is credential.json
        GoogleCredentials credentials = GoogleCredentials.fromStream(stream);
        TextToSpeechSettings textToSpeechSettings =
                TextToSpeechSettings.newBuilder()
                        .setCredentialsProvider(
                                FixedCredentialsProvider.create(credentials)
                        ).build();

在這種情況下如何傳遞上下文？

Answer 1

我需要做的是將我的 Dialog class 的getActivity()傳遞給MainActivity() 。 我能夠使用接口和onAttach()做到這一點：

public interface OnInputListener {
    void customTts(String input, Activity activity);
}
public OnInputListener onInputListener;

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    try {
        onInputListener = (OnInputListener) getActivity();
    }
    catch (ClassCastException e) {
        Log.e(TAG, "onAttach: ClassCastException: " + e.getMessage());
    }
}

這是我按下按鈕時使用的：

onInputListener.customTts(input, getActivity());

在我的 MainActivity class 中，我將customTts()方法更改為：

@RequiresApi(api = Build.VERSION_CODES.KITKAT)
@Override
public void customTts(String input, Activity activity) {
    Tts tts = new Tts(activity, _mediaPlayer, barTop, barBottom);
    try {
        tts.say(input);
    } catch (Exception e) {
        e.printStackTrace();
    }
}