如何测试firestore中是否存在文档?

如何测试firestore中是否存在文档?

我想测试firestore中是否存在文档,我尝试了以下操作:

mDocRef.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
            @Override
            public void onSuccess(DocumentSnapshot documentSnapshot) {
                Settings activity = activityReference.get();
                if (documentSnapshot.exists()) {
                    usable = false;
                    Log.d("checkIfUsable", String.valueOf(usable));
                } else {
                    usable = true;
                    Log.d("checkIfUsable", String.valueOf(usable));
                }
            }
        });

我可以在日志中看到消息,但变量 可用的 未及时更新。之后的代码应该在完成文档存在性测试后执行。

我认为使用AsyncTask可能会起作用,但事实并非如此。以下是我所做的:

private static class checkIfUsable extends AsyncTask<String, Void, Void> {

    private WeakReference<Settings> activityReference;
    // only retain a weak reference to the activity
    checkIfUsable(Settings context) {
        activityReference = new WeakReference<>(context);
    }

    private WeakReference<Application> appReference;

    checkIfUsable(Application context) {
        appReference = new WeakReference<>(context);
    }

    @Override
    protected Void doInBackground(String... strings) {

        DocumentReference mDocRef = FirebaseFirestore.getInstance().document("savedSampleData/" + Arrays.toString(strings));

        mDocRef.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
            @Override
            public void onSuccess(DocumentSnapshot documentSnapshot) {
                Settings activity = activityReference.get();
                if (documentSnapshot.exists()) {
                    activity.usable = false;
                    Log.d("checkIfUsable", String.valueOf(activity.usable));
                } else {
                    activity.usable = true;
                    Log.d("checkIfUsable", String.valueOf(activity.usable));
                }
            }
        });
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        Settings activity = activityReference.get();
        if (activity.usable) {
            final SharedPreferences sharedPreferences = activity.getSharedPreferences(SETTINGS_SHARED_PREF_FILE_KEY, Context.MODE_PRIVATE);
            SharedPreferences.Editor editor = sharedPreferences.edit();
            editor.putString(PERSONAL_SAMPLE_CODE_KEY, String.valueOf(activity.text));
            editor.apply();
            activity.update();
        } else {
            Toast.makeText(appReference.get(), R.string.something_went_wrong_check_internet_or_use_other_code, Toast.LENGTH_LONG).show();
        }
    }
}

我在构造器上发现了这个错误 new checkIfUsable().execute();

无法解析构造函数

是否有其他方法检查文档是否存在? 我是否将AsyncTask编码错误?

谢谢你的帮助