Android 进度条无法正常工作

Question

I am trying to fetch a list of earthquakes using an API. All I want is that, if internet connection is not available, the screen must tell about it to the user, else while data has not yet been fetched, a progress bar should show up to let the user know that fetching is in progress and when done fetching, the progress bar goes away and the recycler view displays the list of earthquakes. But for some reason, the progress bar is now working properly. Either it doesn't show up at all or if it does, it doesn't go away . Here is my Main Activity class:

public class EarthquakeActivity extends AppCompatActivity {

    private MyModel mMyModel;
    private ViewModelProvider mViewModelProvider;
    private RecyclerView mRecyclerView;
    private TextView mEmptyView;
    private EarthquakeAdapter mEarthquakeAdapter;
    private ProgressBar mProgressBar;
    private ConnectivityManager mConnectivityManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.earthquake_activity);
        mEmptyView = findViewById(R.id.empty_view);
        // get the progress bar to indicate loading
        mProgressBar = findViewById(R.id.loading_bar);
        // set a view model provider for the current activity
        mViewModelProvider = new ViewModelProvider(this);
        // get the view model for the class
        mMyModel = mViewModelProvider.get(MyModel.class);
        // find a reference to the {@link RecyclerView} in the layout
        mRecyclerView = findViewById(R.id.earthquakes);
        mConnectivityManager = getSystemService(ConnectivityManager.class);
        mEmptyView.setText("No internet available");
        mEmptyView.setVisibility(View.VISIBLE);
        Handler handler = new Handler(Looper.getMainLooper());
        mConnectivityManager.registerDefaultNetworkCallback(new ConnectivityManager.NetworkCallback(){
            @Override
            public void onAvailable(Network network) {
                handler.post(new Runnable() {
                    @Override
                    public void run() {
                        mEmptyView.setVisibility(View.GONE);
                        mProgressBar.setVisibility(View.VISIBLE);
                        fetchData();
                    }
                });
            }
        });
        mProgressBar.setVisibility(View.GONE);// hide the progress bar
        mRecyclerView.setVisibility(View.VISIBLE);// make the recycler view visible
    }

    private void fetchData(){
        // fetch the list of earthquakes
        mMyModel.getEarthquakes().observe(EarthquakeActivity.this, new Observer<ArrayList<Earthquake>>() {
            @Override
            public void onChanged(ArrayList<Earthquake> earthquakes) {
                // set up recycler view with this data, this will work even if you rotate the device
                setUpRecyclerView(earthquakes);
            }
        });
    }

    private void setUpRecyclerView(ArrayList<Earthquake> earthquakes) {
        if(earthquakes == null || earthquakes.size() == 0) {
            mRecyclerView.setVisibility(View.GONE);
            mProgressBar.setVisibility(View.GONE);
            mEmptyView.setText(R.string.no_data_available);
            mEmptyView.setVisibility(View.VISIBLE);
        }
        else {
            mRecyclerView.setVisibility(View.VISIBLE);
            mEmptyView.setVisibility(View.GONE);
            // create adapter passing in the earthquake data
            mEarthquakeAdapter = new EarthquakeAdapter(EarthquakeActivity.this, earthquakes);
            // attach the adapter to the recyclerView to populate the items
            mRecyclerView.setAdapter(mEarthquakeAdapter);
            // set the layout manager to position the items
            mRecyclerView.setLayoutManager(new LinearLayoutManager(EarthquakeActivity.this));
            // click listener for when an item is clicked
            mEarthquakeAdapter.setClickListener((view, position) -> searchWeb(earthquakes.get(position).getUrl()));
        }
    }

    private void searchWeb(String url) {
        Intent intent = new Intent(Intent.ACTION_WEB_SEARCH);
        intent.putExtra(SearchManager.QUERY,url);
        if(intent.resolveActivity(getPackageManager()) != null) {
            startActivity(intent);
        }
    }
}

and my recycler view xml file

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/earthquakes"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:visibility="gone"
        />
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/empty_view"
        android:layout_centerInParent="true"
        android:visibility="gone"
        android:textAppearance="?android:textAppearanceMedium"
        android:text="@string/no_data_available"
        />
    <ProgressBar
        android:id="@+id/loading_bar"
        style="?android:attr/progressBarStyle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:indeterminate="true"
        android:visibility="gone"
        />


</RelativeLayout>

In case needed, here is my MyModel.java file which itself was a herculean task to setup properly

public class MyModel extends ViewModel {

    private static final String LOG_TAG = "MyModel";
    public MutableLiveData<ArrayList<Earthquake>> mMutableLiveData;
    public ArrayList<Earthquake> mEarthquakes;

    public MutableLiveData<ArrayList<Earthquake>> getEarthquakes() {
        mMutableLiveData = new MutableLiveData<>();
        // call the API
        init();
        return mMutableLiveData;
    }

    public void init() {
        // perform the network request on separate thread
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        executorService.execute(new Runnable() {
            @Override
            public void run() {
                // create array list of earthquakes
                mEarthquakes = QueryUtils.fetchEarthquakeData("https://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=2021-06-01&limit=300");
                mMutableLiveData.postValue(mEarthquakes);
            }
        });
        executorService.shutdown();

    }


}

Please explain what I am doing wrong. I recently learnt multithreading and API basics so I don't have any idea about my mistake. I would appreciate the help.

Answer 1

Try to change this in your MainActivity =>

mConnectivityManager.registerDefaultNetworkCallback(new ConnectivityManager.NetworkCallback(){
        @Override
        public void onAvailable(Network network) {
            handler.post(new Runnable() {
                @Override
                public void run() {
                    
                    fetchData();
                }
            });
        }
    }).addOnCompleteListener(new View.OnCompleteListener) {
       mEmptyView.setVisibility(View.GONE);
                    mProgressBar.setVisibility(View.VISIBLE);});