android - 下载管理器有时显示不成功

Question

正如标题所说，我有一个下载管理器，它可以工作，但只是有时。这很奇怪，我找不到模式。我有一个按钮，单击该按钮会向服务器发送请求，服务器返回要下载的文件，然后有时会下载，有时不会。我看不到任何模式，也没有从电话或服务器收到任何错误。

这对我的应用程序不利，因为我需要知道它已成功下载，所以我要么需要找出它有时不起作用的原因，要么找到一种在下载失败时运行函数的方法。这是我用来下载文件的代码:

        GlobalVariables globalVariables = new GlobalVariables();
        String url = globalVariables.getIPAddress() + "downloadsong/" + Integer.toString(songId) + "/";
        SharedPreferences sharedPreferences = getSharedPreferences("StoredValues", MODE_PRIVATE);
        String token = sharedPreferences.getString("token", "null");

        DownloadManager downloadManager = (DownloadManager)getSystemService(DOWNLOAD_SERVICE);
        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
        request.setTitle("Downloading");
        request.setDescription("Downloading new titles");
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
        request.setDestinationInExternalPublicDir(Environment.DIRECTORY_MUSIC, "" + songId + ".mp3");
        request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);
        request.addRequestHeader("Authorization", "Token " + token);
        request.allowScanningByMediaScanner();
        request.setAllowedOverMetered(true);
        request.setAllowedOverRoaming(true);

        long downloadReference = downloadManager.enqueue(request);
        if (downloadReference != 0) {
            Toast.makeText(getApplicationContext(), "download started", Toast.LENGTH_SHORT).show();
        }else {
            Toast.makeText(getApplicationContext(), "no download started", Toast.LENGTH_SHORT).show();
        }

感谢任何帮助或见解。谢谢!

Answer 1

这是我的例子:

public class MainActivity extends AppCompatActivity {

private Button button;
private long downloadID;

private BroadcastReceiver onDownloadComplete = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        long id = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
        if (downloadID == id) {
            validDownload(MainActivity.this, downloadID);
        }
    }
};

public void validDownload(Context context, long downloadId) {
    DownloadManager dm = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
    if (dm != null) {
        try (Cursor c = dm.query(new DownloadManager.Query().setFilterById(downloadId))) {
            if (c.moveToFirst()) {
                int status = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
                if (status == DownloadManager.STATUS_SUCCESSFUL) {
                    Toast.makeText(MainActivity.this, "Success", Toast.LENGTH_LONG).show();
                } else if (status == DownloadManager.STATUS_FAILED) {
                    Toast.makeText(MainActivity.this, "Failed", Toast.LENGTH_LONG).show();
                }
            }
        }
    }
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    button = findViewById(R.id.download);
    registerReceiver(onDownloadComplete, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
            if (downloadManager != null) {
                downloadID = downloadManager.enqueue(prepareDownloadRequest());
            }
        }
    });
}

private DownloadManager.Request prepareDownloadRequest() {
    File file = new File(getExternalFilesDir(null), "Dummy");
    DownloadManager.Request request = new DownloadManager.Request(Uri.parse("http://speedtest.ftp.otenet.gr/files/test10Mb.db"))
            .setTitle("Dummy File")
            .setDescription("Downloading")
            .setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE)
            .setDestinationUri(Uri.fromFile(file))// Uri of the destination file
            .setAllowedOverMetered(true)
            .setAllowedOverRoaming(true);// Set if download is allowed on roaming networ
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
        request.setRequiresCharging(false);
    }
    return request;
}