如何使用Volley库在Android中按下home键继续下载文件

dependencies {
    implementation 'com.android.volley:volley:1.2.0'
}

import android.content.Context;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.Volley;

public class DownloadQueue {
    private static DownloadQueue instance;
    private RequestQueue requestQueue;
    private static Context context;

    private DownloadQueue(Context context) {
        this.context = context;
        requestQueue = getRequestQueue();
    }

    public static synchronized DownloadQueue getInstance(Context context) {
        if (instance == null) {
            instance = new DownloadQueue(context);
        }
        return instance;
    }

    public RequestQueue getRequestQueue() {
        if (requestQueue == null) {
            requestQueue = Volley.newRequestQueue(context.getApplicationContext());
        }
        return requestQueue;
    }

    public <T> void addToRequestQueue(Request<T> request) {
        getRequestQueue().add(request);
    }
}

import android.content.Context;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.toolbox.StringRequest;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class FileDownloadRequest extends StringRequest {
    private String fileUrl;
    private String filePath;

    public FileDownloadRequest(String fileUrl, String filePath, Response.Listener<String> listener, Response.ErrorListener errorListener) {
        super(Method.GET, fileUrl, listener, errorListener);
        this.fileUrl = fileUrl;
        this.filePath = filePath;
    }

    @Override
    public byte[] getBody() {
        return null;
    }

    @Override
    public String getBodyContentType() {
        return null;
    }

    @Override
    public void deliverResponse(String response) {
        // 下载完成后的处理逻辑
    }

    @Override
    protected Response<String> parseNetworkResponse(com.android.volley.NetworkResponse response) {
        try {
            InputStream inputStream = response.data;
            OutputStream outputStream = new FileOutputStream(filePath);
            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            outputStream.close();
            inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return super.parseNetworkResponse(response);
    }
}

import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.view.KeyEvent;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;

public class MainActivity extends AppCompatActivity {
    private static final String FILE_URL = "http://example.com/file.txt";
    private static final String FILE_PATH = Environment.getExternalStorageDirectory().getPath() + "/file.txt";
    private static final String KEY_DOWNLOAD_IN_PROGRESS = "download_in_progress";
    private boolean downloadInProgress;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (savedInstanceState != null) {
            downloadInProgress = savedInstanceState.getBoolean(KEY_DOWNLOAD_IN_PROGRESS);
        }

        if (!downloadInProgress) {
            startDownload();
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putBoolean(KEY_DOWNLOAD_IN_PROGRESS, downloadInProgress);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_HOME) {
            // 按下Home键时保存下载状态
            downloadInProgress = true;
        }
        return super.onKeyDown(keyCode, event);
    }

    private void startDownload() {
        FileDownloadRequest request = new FileDownloadRequest(FILE_URL, FILE_PATH,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        // 下载完成的回调
                        Toast.makeText(MainActivity.this, "文件下载完成", Toast.LENGTH_SHORT).show();
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        // 下载出错的回调
                        Toast.makeText(MainActivity.this, "文件下载出错", Toast.LENGTH_SHORT).show();
                    }
                });

        DownloadQueue.getInstance(this).addToRequestQueue(request);
    }
}