Android进度条无法正常工作

Question

我正在尝试使用 API 获取地震列表。我想要的是，如果互联网连接不可用，屏幕必须告诉用户，否则在尚未获取数据时，应该显示一个进度条，让用户知道正在获取以及何时提取完成后，进度条消失，回收站视图显示地震列表。但是由于某种原因，进度条现在可以正常工作。要么根本不出现，要么即使出现，也不会消失。这是我的主要活动课程：

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);
        }
    }
}

和我的回收站视图 xml 文件

<?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>

如果需要，这是我的 MyModel.java 文件，它本身是一项艰巨的任务，要正确设置

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();

    }


}

请解释我做错了什么。我最近学习了多线程和 API 基础知识，所以我对自己的错误一无所知。我将不胜感激。

Answer 1

尝试在您的 MainActivity 中更改此设置 =>

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);});