12

我正在尝试从 Internet 下载大文件 (>20Mb)

private class DownloadTask extends AsyncTask<DatabaseInfo, Integer, String> {

    private DatabaseInfo info;

    protected String doInBackground(DatabaseInfo... dbInfo) {

        int count;
        info = dbInfo[0];

        try {

            URL url = new URL(dbInfo[0].dbPath);

            InputStream input = new BufferedInputStream(url.openStream());
            OutputStream output = new FileOutputStream("/sdcard/db.zip");

            byte data[] = new byte[1024];
            int total = 0;

            while ((count = input.read(data)) != -1) {

                //output.write(data, 0, count);

                total += count;

                if (total % 10240 == 0) {
                    publishProgress(total);
                }
            }

            output.flush();
            output.close();
            input.close();
        } 
        catch (Exception e) {
            Log.e("err", e.getMessage());
        }

        return null;
    }

    protected void onProgressUpdate(Integer... total) {

        int perc = (int) ((float) total[0] / (float) info.dbZipSize * 100);
        mProgressDialog.setProgress(perc);
    }

    protected void onPostExecute(String s) {

        dismissDialog(DIALOG_PROGRESS);
        Log.e("err", "finish!");
    }
}

如果我取消注释行

//output.write(data, 0, count);

下载进度条对话框关闭 7-15% 后,我看到“完成!” 在日志中。为什么?

4

2 回答 2

6

您应该查看实现 HTTP 范围。这将允许您在下载失败时重新开始下载。

至于为什么停止,一些运营商实施下载限制,在一定时间或下载量后会断开连接。我在一家英国运营商上亲眼目睹了这一点,并在其他运营商上被告知过。通过尝试通过 Android 浏览器下载文件通常很容易验证限制,如果您看到它停止或停止,您知道这很可能是运营商问题(是的,下载可以终止而不会引发异常)。

Http Range 实现将允许您从中断的位置继续下载,因此您的 doInBackground 方法可以使用延迟和恢复算法,以便每次连接中断时您等待一段时间然后尝试在哪里恢复下载停止(当然,实施重试限制,这样当手机真的无法下载文件时,您就不会陷入无限循环)。

于 2010-07-01T07:48:46.357 回答
0

有一个非常好的库可以处理所有这些,并且在网络由于某种未知原因而脱机的情况下具有恢复功能。android 库称为 PRDownloader,可在 Github 上获取: https ://github.com/MindorksOpenSource/PRDownloader

首先你需要把它添加到你的 gradle 文件中,像这样(当前版本 os 0.6.0)

    implementation 'com.mindorks.android:prdownloader:0.6.0'

之后,可以在我开发的应用程序中实现的类中使用它,如下所示。它使用进度对话框并显示下载的百分比,并且如上所述,当网络脱机或用户退出应用程序时,它能够在以后获取下载。可以根据具体需要进行调整,代码如下:

public class DownloadManager {
private MainActivity activity;
private ProgressDialog progressDialog;

private int downloadStatus;
private String filename="";

private static String dirPath;
private String URL = "https://someurl.com/dummyfile.pdf";

public DownloadManager(MainActivity _activity){
    this.activity=_activity;
    dirPath = Utils.getRootDirPath(activity);
    downloadStatus=0;
}

public void setDownloadUrl(String url){
    this.URL=url;
}

public String getFileNameDirPath(){
    return dirPath+"/"+filename;
};

public void setFilename(String filename){
    this.filename=filename;
}
public String getFilename(){
    return this.filename;
}
public String getDirectoryPath(){
    return this.filename;
}

public void startFileDownload(){
    if (Status.RUNNING == PRDownloader.getStatus(downloadStatus)) {
        PRDownloader.pause(downloadStatus);
        return;
    }

    this.progressDialog = new ProgressDialog(this.activity);
    this.progressDialog.setIndeterminate(true);
    this.progressDialog.setTitle("Title");
    this.progressDialog.setMessage("Downloading file...");
    this.progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
    this.progressDialog.setCancelable(false);
    this.progressDialog.setMax(100);
    this.progressDialog.show();

    if (Status.PAUSED == PRDownloader.getStatus(downloadStatus)) {
        PRDownloader.resume(downloadStatus);
        return;
    }

    downloadStatus = PRDownloader.download(URL, dirPath, this.filename)
            .build()
            .setOnStartOrResumeListener(new OnStartOrResumeListener() {
                @Override
                public void onStartOrResume() {
                    progressDialog.setIndeterminate(false);
                }
            })
            .setOnPauseListener(new OnPauseListener() {
                @Override
                public void onPause() {
                }
            })
            .setOnCancelListener(new OnCancelListener() {
                @Override
                public void onCancel() {
                    progressDialog.setProgress(0);
                    downloadStatus = 0;
                    progressDialog.setIndeterminate(false);
                    progressDialog.dismiss();
                }
            })
            .setOnProgressListener(new OnProgressListener() {
                @Override
                public void onProgress(Progress progress) {
                    long progressPercent = progress.currentBytes * 100 / progress.totalBytes;
                    progressDialog.setProgress((int) progressPercent);
                    progressDialog.setIndeterminate(false);
                }
            })
            .start(new OnDownloadListener() {
                @Override
                public void onDownloadComplete() {
                    progressDialog.dismiss();
                    activity.fragmentManagement.setCurrentFragment("MapFragment");
                }

                @Override
                public void onError(Error error) {

                    Toast.makeText(activity, "Error downloading file", Toast.LENGTH_SHORT).show();
                    progressDialog.setProgress(0);
                    downloadStatus = 0;
                    progressDialog.setIndeterminate(false);
                    progressDialog.dismiss();
                }
            });
}

public static final class Utils {

    private Utils() {
        // no instance
    }

    public static String getRootDirPath(Context context) {
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            File file = ContextCompat.getExternalFilesDirs(context.getApplicationContext(),
                    null)[0];
            return file.getAbsolutePath();
        } else {
            return context.getApplicationContext().getFilesDir().getAbsolutePath();
        }
    }

    public  static String getProgressDisplayLine(long currentBytes, long totalBytes) {
        return getBytesToMBString(currentBytes) + "/" + getBytesToMBString(totalBytes);
    }

    private static String getBytesToMBString(long bytes){
        return String.format(Locale.ENGLISH, "%.2fMb", bytes / (1024.00 * 1024.00));
    }

}

}

于 2020-11-12T21:07:46.447 回答