在Android中使用AsynkTaskLoader从Cloud Firestore检索数据

Question

我是Android和Firebase的新手，并且遇到了一个我不明白的怪异错误。 我有一个RecyclerView，它应该显示一个字符串列表，该字符串列表的日期后面是一个数字。 现在，我想从Cloud Firestore检索数据并显示它。 为此，我使用AsyncTaskLoader，并在loadInBackground()从Cloud Firestore检索数据。 现在，当我开始活动时，它会显示错误消息（无论我按了多少次刷新按钮，它都会一直保持这种行为）。 但是，如果我关闭屏幕然后再打开，它将以我希望的方式显示数据。 以下是我的代码

public class MeasureListActivity extends AppCompatActivity implements
    MeasuresAdapter.MeasuresAdapterOnClickHandler,
    LoaderManager.LoaderCallbacks<String[]> {

private RecyclerView mRecyclerView;

private FirebaseAuth mAuth;
private MeasuresAdapter mMeasuresAdapter;

private TextView mErrorMessageDisplay;

private ProgressBar mLoadingIndicator;

private static final int MEASURES_LOADER_ID = 0;


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    /* Use AppCompatActivity's method getMenuInflater to get a handle on the menu inflater */
    MenuInflater inflater = getMenuInflater();
    /* Use the inflater's inflate method to inflate our menu layout to this menu */
    inflater.inflate(R.menu.measures_list, menu);
    /* Return true so that the menu is displayed in the Toolbar */
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();

    if (id == R.id.action_refresh) {
        invalidateData();
        getSupportLoaderManager().restartLoader(MEASURES_LOADER_ID, null, this);
        return true;
    }
    return super.onOptionsItemSelected(item);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_measure_list);

    mAuth = FirebaseAuth.getInstance();

    mRecyclerView = (RecyclerView) findViewById(R.id.recyclerview_measures);

    mErrorMessageDisplay = (TextView) findViewById(R.id.tv_error_message_display);

    LinearLayoutManager layoutManager
            = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);

    mRecyclerView.setLayoutManager(layoutManager);

    mRecyclerView.setHasFixedSize(true);

    mMeasuresAdapter = new MeasuresAdapter(this);

    mRecyclerView.setAdapter(mMeasuresAdapter);

    mLoadingIndicator = (ProgressBar) findViewById(R.id.pb_loading_indicator);

    int loaderId = MEASURES_LOADER_ID;

    LoaderManager.LoaderCallbacks<String[]> callback = MeasureListActivity.this;

    Bundle bundleForLoader = null;

    getSupportLoaderManager().initLoader(loaderId, bundleForLoader, callback);
}

@Override
public Loader<String[]> onCreateLoader(int id, final Bundle loaderArgs) {



    return new AsyncTaskLoader<String[]>(this) {

        String[] mWMeasuresData = null;

        @Override
        protected void onStartLoading() {
            if (mWMeasuresData != null) {
                deliverResult(mWMeasuresData);
            } else {
                mLoadingIndicator.setVisibility(View.VISIBLE);
                forceLoad();
            }
        }


        private String[] aux;
        @Override
        public String[] loadInBackground() {


            FirebaseFirestore db = FirebaseFirestore.getInstance();

            db.collection("medidas").whereEqualTo("id_user", "3Aq3g0czkarT8GIbyESV").get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                @Override
                public void onComplete(@NonNull Task<QuerySnapshot> task) {
                    if (task.isSuccessful()) {
                        QuerySnapshot snapshot = task.getResult();
                        int tam = snapshot.getDocuments().size();
                        aux = new String[tam];
                        for (int i = 0; i < tam; i++) {
                            String temp = "";
                            DocumentSnapshot doc = snapshot.getDocuments().get(i);
                            temp += doc.get("fecha") + " ";
                            temp += doc.get("valor");
                            aux[i] = temp;
                        }

                    }
                }
            });

            return aux;
        }


        public void deliverResult(String[] data) {
            mWMeasuresData = data;
            super.deliverResult(data);
        }
    };
}

@Override
public void onLoadFinished(Loader<String[]> loader, String[] data) {
    mLoadingIndicator.setVisibility(View.INVISIBLE);
    mMeasuresAdapter.setMeasuresData(data);
    if (null == data) {
        showErrorMessage();
    } else {
        showMeasuresDataView();
    }
}

@Override
public void onLoaderReset(Loader<String[]> loader) {

}


private void invalidateData() {
    mMeasuresAdapter.setMeasuresData(null);
}


private void showMeasuresDataView() {
    /* First, make sure the error is invisible */
    mErrorMessageDisplay.setVisibility(View.INVISIBLE);
    /* Then, make sure the weather data is visible */
    mRecyclerView.setVisibility(View.VISIBLE);
}

private void showErrorMessage() {
    /* First, hide the currently visible data */
    mRecyclerView.setVisibility(View.INVISIBLE);
    /* Then, show the error */
    mErrorMessageDisplay.setVisibility(View.VISIBLE);
}
@Override
public void onClick(String measure) {
    Context context = this;
    Class destinationClass = DetailMeasureActivity.class;
    Intent intentToStartDetailActivity = new Intent(context, destinationClass);
    intentToStartDetailActivity.putExtra(Intent.EXTRA_TEXT, measure);
    startActivity(intentToStartDetailActivity);
}

}

您能帮我吗？...提前感谢

Answer 1

首先，我认为当您调用以下代码块时：

 mLoadingIndicator.setVisibility(View.VISIBLE);
            forceLoad();

您还应该隐藏错误消息视图。

另外，更重要的是，您不需要AsyncTaskLoader即可从firestore中获取数据，firebase firestore已经为您处理了后台工作。

为了能够全面了解问题的根源，您需要了解活动的生命周期，并添加日志以标记重要事件，以帮助您随时了解哪个代码块被调用。 因此，我鼓励您在数据加载开始，完成，隐藏视图或显示视图时添加日志，以确保所有方法都已调用，并且还将日志添加到活动生命周期中。