android - AsyncTask 和 Firebase

Question

我正在尝试使用 RecyclerView 加载 ListView，但加载的只有进度条，列表未显示。我在 AsyncTask 类中使用 Firebase。我哪里错了？下面是我的代码。

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    public static String KEY_HEADLINES="headlines";
    public static String KEY_DETAILS="details";

    ProgressBar pb;

   public  List<NewsModel> newslist;

   public NewsAdapter2 adapter;
    private RecyclerView mRecyclerView;

    private DatabaseReference mRef;
    ImageView image_news;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // call the array list
        newslist = new ArrayList<NewsModel>();

        pb = (ProgressBar) findViewById(R.id.progressBarNews);
        image_news =(ImageView) findViewById(R.id.image_news);
        mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
       mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        //Enabling offline capabilities
        FirebaseDatabase.getInstance().setPersistenceEnabled(true);

         // firebase initialisation......
        mRef =  FirebaseDatabase.getInstance().getReference("News");
        // keep my data synced
        mRef.keepSynced(true);


//firebase

        //initializing async task
  new  MyTask();

        // load data

        //declare the toolbar
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
    }

    public void LoadData (DataSnapshot dataSnapshot){
        System.out.println(dataSnapshot.getValue());

        NewsModel news_model =dataSnapshot.getValue(NewsModel.class);

        newslist.add(news_model);

        adapter = new NewsAdapter2(MainActivity.this, newslist);
        mRecyclerView.setAdapter(adapter);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();
        Intent i;
        if (id == R.id.hospitals) {
            i = new Intent(MainActivity.this, HealthCentres.class);
            startActivity(i);
        } else if (id == R.id.doctors) {
            i = new Intent(MainActivity.this, Doctors.class);
            startActivity(i);

        } else if (id == R.id.tips) {
            i = new Intent(MainActivity.this, Tips.class);
            startActivity(i);

        }
        else if (id == R.id.contacts) {
            i= new Intent(MainActivity.this, ContactUs.class);
            startActivity(i);

        }
        else if (id == R.id.about) {
            i = new Intent(MainActivity.this, AboutUs.class);
            startActivity(i);
        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

private class MyTask extends AsyncTask<String,String,String>
{

    @Override
    protected void onPreExecute() {

        pb.setVisibility(View.VISIBLE);
        super.onPreExecute();
    }


    @Override
    protected String doInBackground(String... params) {
        mRef.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                LoadData(dataSnapshot);
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                LoadData(dataSnapshot);
            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) { }
            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String s) { }
            @Override
            public void onCancelled(DatabaseError databaseError) { }
        });

        return null;
    }

    @Override
    protected void onPostExecute(String s) {
        pb.setVisibility(View.INVISIBLE);
        super.onPostExecute(s);
    }
}















}

Answer 1

Firebase 已经有了它的异步 litsener ，所以你可以把它放在 onCreate 方法中。但是你说进度条是唯一可见的，只是在onChildEventLitsener()方法pb.setVisibility(View.INVISIBLE);中也加入了这行代码，所以当数据到来时，进度条消失。

mRef.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                pb.setVisibility(View.INVISIBLE);
                LoadData(dataSnapshot);
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                LoadData(dataSnapshot);
            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String s) {

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

希望这一切顺利。