如何使用 Swipe Refresh Layout 刷新内容？

Question

我正在从 UDACITY 学习网络，在那里我遇到了一个名为 Quake Report 的应用程序，我想在应用程序中添加滑动刷新功能，但我无法获得我想要的结果。

package com.example.android.quakereport;

import android.app.LoaderManager;
import android.content.Context;
import android.content.Intent;
import android.content.Loader;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;

import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class EarthquakeActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<List<Earthquake>> {

    /**
     * Constant value for the earthquake loader ID. We can choose any integer.
     * This really only comes into play if you're using multiple loaders.
     */
    private static final int EARTHQUAKE_LOADER_ID = 1;

    //    TextView that is displayed when the list is empty
    private TextView mEmptyStateTextView;

    //    progress bar
    private ProgressBar progressBar;

    public static final String LOG_TAG = EarthquakeActivity.class.getName();

    //    URL for earthquake data from the USGS dataset
    private static final String USGS_REQUEST_URL =
            "https://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&orderby=time&minmag=5&limit=15";


    /**
     * Adapter for the list of earthquakes
     */
    private EarthquakeAdapter mAdapter;

    @Override
    public Loader<List<Earthquake>> onCreateLoader(int id, Bundle args) {
        Log.i(LOG_TAG, "Test: onCreateLoader() called...");
//        Create a new loader for the given URL
        return new EarthquakeLoader(this, USGS_REQUEST_URL);
    }

    @Override
    public void onLoadFinished(Loader<List<Earthquake>> loader, List<Earthquake> data) {
        Log.i(LOG_TAG, "Test: onLoadFinished() called...");
//        Clear the adapter of previous earthquake data
        mAdapter.clear();

//        Hiding the progress bar as the results have been loaded
        progressBar.setVisibility(View.GONE);

//        Check if Internet Connection is present or not and show text accordingly
        ConnectivityManager connManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connManager.getActiveNetworkInfo();

        if (networkInfo != null && networkInfo.isConnected()) {
            mEmptyStateTextView.setText(R.string.no_earthquakes);
        } else {
            mEmptyStateTextView.setText(R.string.no_internet_connection);
        }


//        If there is a valid list of {@link Earthquake}s, then add them to the adapter's
//        data set. This will trigger the ListView to update.
        if (data != null && !data.isEmpty()) {
            mAdapter.addAll(data);
        }
    }

    @Override
    public void onLoaderReset(Loader<List<Earthquake>> loader) {
        Log.i(LOG_TAG, "Test: onLoaderReset() called...");
//        Loader reset, so we can clear out our existing data.
        mAdapter.clear();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.i(LOG_TAG, "Test: Earthquake Activity onCreate() called.");

        super.onCreate(savedInstanceState);
        setContentView(R.layout.earthquake_activity);

//        Creating a swipe to refresh feature
        final SwipeRefreshLayout pullToRefresh = findViewById(R.id.swipe_refresh);
        pullToRefresh.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {

                pullToRefresh.setRefreshing(false);
            }
        });

        // Find a reference to the {@link ListView} in the layout
        ListView earthquakeListView = (ListView) findViewById(R.id.list);

        // Get a reference to the ConnectivityManager to check state of network connectivity
        ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

        // Get details on the currently active default data network
        NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();

        // If there is a network connection, fetch data
        if (networkInfo != null && networkInfo.isConnected()) {
            //        Get a reference to the LoaderManager, in order to interact with loaders.
            LoaderManager loaderManager = getLoaderManager();

            // Initialize the loader. Pass in the int ID constant defined above and pass in null for
            // the bundle. Pass in this activity for the LoaderCallbacks parameter (which is valid
            // because this activity implements the LoaderCallbacks interface).
            // Create a new adapter that takes an empty list of earthquakes as input
            Log.i(LOG_TAG, "Test: calling initLoader()...");
            loaderManager.initLoader(EARTHQUAKE_LOADER_ID, null, this);
        } else {
            // Otherwise, display error
            // First, hide loading indicator so error message will be visible
            progressBar = (ProgressBar) findViewById(R.id.progress_bar);
            progressBar.setVisibility(View.GONE);

            // Update empty state with no connection error message
            mEmptyStateTextView = (TextView) findViewById(R.id.empty_view);
            mEmptyStateTextView.setText(R.string.no_internet_connection);
        }

        mEmptyStateTextView = (TextView) findViewById(R.id.empty_view);
        earthquakeListView.setEmptyView(mEmptyStateTextView);

        progressBar = (ProgressBar) findViewById(R.id.progress_bar);

        mAdapter = new EarthquakeAdapter(this, new ArrayList<Earthquake>());

        // Set the adapter on the {@link ListView}
        // so the list can be populated in the user interface
        earthquakeListView.setAdapter(mAdapter);

        // Set an item click listener on the ListView, which sends an intent to a web browser
        // to open a website with more information about the selected earthquake.
        earthquakeListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                // Find the current earthquake that was clicked on
                Earthquake currentEarthquake = mAdapter.getItem(position);

                // Convert the String URL into a URI object (to pass into the Intent constructor)
                Uri earthquakeUri = Uri.parse(currentEarthquake.getUrl());

                // Create a new intent to view the earthquake URI
                Intent websiteIntent = new Intent(Intent.ACTION_VIEW, earthquakeUri);

                // Send the intent to launch a new activity
                startActivity(websiteIntent);
            }
        });

//        EarthquakeAsyncTask task = new EarthquakeAsyncTask();
//        task.execute(USGS_REQUEST_URL);
    }

    /**
     * {@link AsyncTask} to perform the network request on a background thread, and then
     * update the UI with the list of earthquakes in the response.
     * <p>
     * AsyncTask has three generic parameters: the input type, a type used for progress updates, and
     * an output type. Our task will take a String URL, and return an Earthquake. We won't do
     * progress updates, so the second generic is just Void.
     * <p>
     * We'll only override two of the methods of AsyncTask: doInBackground() and onPostExecute().
     * The doInBackground() method runs on a background thread, so it can run long-running code
     * (like network activity), without interfering with the responsiveness of the app.
     * Then onPostExecute() is passed the result of doInBackground() method, but runs on the
     * UI thread, so it can use the produced data to update the UI.
     */
    private class EarthquakeAsyncTask extends AsyncTask<String, Void, List<Earthquake>> {

        /**
         * This method runs on a background thread and performs the network request.
         * We should not update the UI from a background thread, so we return a list of
         * {@link Earthquake}s as the result.
         */
        @Override
        protected List<Earthquake> doInBackground(String... urls) {
            // Don't perform the request if there are no URLs, or the first URL is null.
            if (urls.length < 1 || urls[0] == null) {
                return null;
            }

            List<Earthquake> result = QueryUtils.fetchEarthquakeData(urls[0]);
            return result;
        }

        /**
         * This method runs on the main UI thread after the background work has been
         * completed. This method receives as input, the return value from the doInBackground()
         * method. First we clear out the adapter, to get rid of earthquake data from a previous
         * query to USGS. Then we update the adapter with the new list of earthquakes,
         * which will trigger the ListView to re-populate its list items.
         */
        @Override
        protected void onPostExecute(List<Earthquake> data) {
            // Clear the adapter of previous earthquake data
            mAdapter.clear();

            // If there is a valid list of {@link Earthquake}s, then add them to the adapter's
            // data set. This will trigger the ListView to update.
            if (data != null && !data.isEmpty()) {
                mAdapter.addAll(data);
            }
        }
    }
}

每当用户向下滑动时，我希望此应用程序从给定的 URL 获取数据，但我无法找到方法。 谁能帮我编写以下代码块中的代码：

final SwipeRefreshLayout pullToRefresh = findViewById(R.id.swipe_refresh);
pullToRefresh.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
    @Override
    public void onRefresh() {

        pullToRefresh.setRefreshing(false);
    }
});

Answer 1

调用 doRefresh 方法中负责网络调用的方法