使用Android下载文件，并在ProgressDialog中显示进度

Question

我正在尝试编写一个更新的简单应用程序。为此，我需要一个简单的函数，可以在ProgressDialog下载文件并显示当前进度。我知道怎么做ProgressDialog，但我不知道如何显示当前进度以及如何首先下载文件。

Answer 1

下载文件的方法有很多种。以下我将发布最常见的方式;您可以自行决定哪种方法更适合您的应用。

1。使用AsyncTask并在对话框中显示下载进度

此方法允许您同时执行一些后台进程并更新UI（在这种情况下，我们将更新进度条）。

这是一个示例代码：

// declare the dialog as a member field of your activity
ProgressDialog mProgressDialog;

// instantiate it within the onCreate method
mProgressDialog = new ProgressDialog(YourActivity.this);
mProgressDialog.setMessage("A message");
mProgressDialog.setIndeterminate(true);
mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mProgressDialog.setCancelable(true);

// execute this when the downloader must be fired
final DownloadTask downloadTask = new DownloadTask(YourActivity.this);
downloadTask.execute("the url to the file you want to download");

mProgressDialog.setOnCancelListener(new DialogInterface.OnCancelListener() {

    @Override
    public void onCancel(DialogInterface dialog) {
        downloadTask.cancel(true); //cancel the task
    }
});

AsyncTask将如下所示：

// usually, subclasses of AsyncTask are declared inside the activity class.
// that way, you can easily modify the UI thread from here
private class DownloadTask extends AsyncTask<String, Integer, String> {

    private Context context;
    private PowerManager.WakeLock mWakeLock;

    public DownloadTask(Context context) {
        this.context = context;
    }

    @Override
    protected String doInBackground(String... sUrl) {
        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(sUrl[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();

            // expect HTTP 200 OK, so we don't mistakenly save error report
            // instead of the file
            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                return "Server returned HTTP " + connection.getResponseCode()
                        + " " + connection.getResponseMessage();
            }

            // this will be useful to display download percentage
            // might be -1: server did not report the length
            int fileLength = connection.getContentLength();

            // download the file
            input = connection.getInputStream();
            output = new FileOutputStream("/sdcard/file_name.extension");

            byte data[] = new byte[4096];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1) {
                // allow canceling with back button
                if (isCancelled()) {
                    input.close();
                    return null;
                }
                total += count;
                // publishing the progress....
                if (fileLength > 0) // only if total length is known
                    publishProgress((int) (total * 100 / fileLength));
                output.write(data, 0, count);
            }
        } catch (Exception e) {
            return e.toString();
        } finally {
            try {
                if (output != null)
                    output.close();
                if (input != null)
                    input.close();
            } catch (IOException ignored) {
            }

            if (connection != null)
                connection.disconnect();
        }
        return null;
    }

上述方法（doInBackground）始终在后台线程上运行。你不应该在那里做任何UI任务。另一方面，onProgressUpdate和onPreExecute在UI线程上运行，因此您可以更改进度条：

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // take CPU lock to prevent CPU from going off if the user 
        // presses the power button during download
        PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
        mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
             getClass().getName());
        mWakeLock.acquire();
        mProgressDialog.show();
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        super.onProgressUpdate(progress);
        // if we get here, length is known, now set indeterminate to false
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.setMax(100);
        mProgressDialog.setProgress(progress[0]);
    }

    @Override
    protected void onPostExecute(String result) {
        mWakeLock.release();
        mProgressDialog.dismiss();
        if (result != null)
            Toast.makeText(context,"Download error: "+result, Toast.LENGTH_LONG).show();
        else
            Toast.makeText(context,"File downloaded", Toast.LENGTH_SHORT).show();
    }

要运行此功能，您需要WAKE_LOCK权限。

<uses-permission android:name="android.permission.WAKE_LOCK" />

2。从服务下载

这里最大的问题是：如何从服务更新我的活动？。在下一个示例中，我们将使用您可能不知道的两个类：ResultReceiver和IntentService。 ResultReceiver允许我们从服务更新我们的线程; IntentService是Service的子类，它产生一个线程来从那里开始后台工作（你应该知道Service实际上在你的app的同一个线程中运行;当你扩展Service时1}}，你必须手动生成新线程来运行CPU阻塞操作。）

下载服务可能如下所示：

public class DownloadService extends IntentService {
    public static final int UPDATE_PROGRESS = 8344;

    public DownloadService() {
        super("DownloadService");
    }
    @Override
    protected void onHandleIntent(Intent intent) {

        String urlToDownload = intent.getStringExtra("url");
        ResultReceiver receiver = (ResultReceiver) intent.getParcelableExtra("receiver");
        try {

            //create url and connect
            URL url = new URL(urlToDownload);
            URLConnection connection = url.openConnection();
            connection.connect();

            // this will be useful so that you can show a typical 0-100% progress bar
            int fileLength = connection.getContentLength();

            // download the file
            InputStream input = new BufferedInputStream(connection.getInputStream());

            String path = "/sdcard/BarcodeScanner-debug.apk" ;
            OutputStream output = new FileOutputStream(path);

            byte data[] = new byte[1024];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1) {
                total += count;

                // publishing the progress....
                Bundle resultData = new Bundle();
                resultData.putInt("progress" ,(int) (total * 100 / fileLength));
                receiver.send(UPDATE_PROGRESS, resultData);
                output.write(data, 0, count);
            }

            // close streams 
            output.flush();
            output.close();
            input.close();

        } catch (IOException e) {
            e.printStackTrace();
        }

        Bundle resultData = new Bundle();
        resultData.putInt("progress" ,100);

        receiver.send(UPDATE_PROGRESS, resultData);
    }
}

将服务添加到您的清单：

<service android:name=".DownloadService"/>

活动将如下所示：

// initialize the progress dialog like in the first example

// this is how you fire the downloader
mProgressDialog.show();
Intent intent = new Intent(this, DownloadService.class);
intent.putExtra("url", "url of the file to download");
intent.putExtra("receiver", new DownloadReceiver(new Handler()));
startService(intent);

以下是ResultReceiver来玩：

private class DownloadReceiver extends ResultReceiver{

    public DownloadReceiver(Handler handler) {
        super(handler);
    }

    @Override
    protected void onReceiveResult(int resultCode, Bundle resultData) {

        super.onReceiveResult(resultCode, resultData);

        if (resultCode == DownloadService.UPDATE_PROGRESS) {

            int progress = resultData.getInt("progress"); //get the progress
            dialog.setProgress(progress);

            if (progress == 100) {
                dialog.dismiss();
            }
        }
    }
}

2.1使用Groundy库

Groundy是一个基本上可以帮助您在后台服务中运行代码段的库，它基于上面显示的ResultReceiver概念。此库目前已弃用。这就是整个代码的样子：

您正在显示对话框的活动......

public class MainActivity extends Activity {

    private ProgressDialog mProgressDialog;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        findViewById(R.id.btn_download).setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                String url = ((EditText) findViewById(R.id.edit_url)).getText().toString().trim();
                Bundle extras = new Bundler().add(DownloadTask.PARAM_URL, url).build();
                Groundy.create(DownloadExample.this, DownloadTask.class)
                        .receiver(mReceiver)
                        .params(extras)
                        .queue();

                mProgressDialog = new ProgressDialog(MainActivity.this);
                mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
                mProgressDialog.setCancelable(false);
                mProgressDialog.show();
            }
        });
    }

    private ResultReceiver mReceiver = new ResultReceiver(new Handler()) {
        @Override
        protected void onReceiveResult(int resultCode, Bundle resultData) {
            super.onReceiveResult(resultCode, resultData);
            switch (resultCode) {
                case Groundy.STATUS_PROGRESS:
                    mProgressDialog.setProgress(resultData.getInt(Groundy.KEY_PROGRESS));
                    break;
                case Groundy.STATUS_FINISHED:
                    Toast.makeText(DownloadExample.this, R.string.file_downloaded, Toast.LENGTH_LONG);
                    mProgressDialog.dismiss();
                    break;
                case Groundy.STATUS_ERROR:
                    Toast.makeText(DownloadExample.this, resultData.getString(Groundy.KEY_ERROR), Toast.LENGTH_LONG).show();
                    mProgressDialog.dismiss();
                    break;
            }
        }
    };
}

Groundy 用于下载文件并显示进度的GroundyTask实现：

public class DownloadTask extends GroundyTask {    
    public static final String PARAM_URL = "com.groundy.sample.param.url";

    @Override
    protected boolean doInBackground() {
        try {
            String url = getParameters().getString(PARAM_URL);
            File dest = new File(getContext().getFilesDir(), new File(url).getName());
            DownloadUtils.downloadFile(getContext(), url, dest, DownloadUtils.getDownloadListenerForTask(this));
            return true;
        } catch (Exception pokemon) {
            return false;
        }
    }
}

然后将其添加到清单中：

<service android:name="com.codeslap.groundy.GroundyService"/>

我认为这不容易。只需抓住最新的jar from Github就可以了。请记住， Groundy 的主要目的是在后台服务中调用外部REST apis，并轻松地将结果发布到UI。如果你在你的应用程序中做了类似的事情，它可能真的很有用。

2.2使用https://github.com/koush/ion

3。使用DownloadManager类（仅GingerBread和更新版本）

GingerBread带来了一个新功能DownloadManager，它允许您轻松下载文件并将处理线程，流等的艰苦工作委派给系统。

首先，让我们看一个实用方法：

/**
 * @param context used to check the device version and DownloadManager information
 * @return true if the download manager is available
 */
public static boolean isDownloadManagerAvailable(Context context) {

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD) {
        return true;
    }
    return false;
}

方法的名称解释了这一切。一旦确定DownloadManager可用，就可以执行以下操作：

String url = "url you want to download";
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
request.setDescription("Some descrition");
request.setTitle("Some title");
// in order for this if to run, you must use the android 3.2 to compile your app
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
    request.allowScanningByMediaScanner();
    request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
}
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "name-of-the-file.ext");

// get download service and enqueue file
DownloadManager manager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
manager.enqueue(request);

下载进度将显示在通知栏中。

最后的想法

第一种和第二种方法只是冰山一角。如果您希望自己的应用程序功能强大，那么您需要记住很多事情。这是一个简短的清单：

• 您必须检查用户是否有可用的互联网连接
• 确保您拥有正确的权限（INTERNET和WRITE_EXTERNAL_STORAGE）;如果您想查看互联网可用性，还可以ACCESS_NETWORK_STATE。
• 确保目录下载文件存在并具有写入权限。
• 如果下载太大，您可能希望实现一种方法，以便在以前的尝试失败时恢复下载。
• 如果您允许用户中断下载，用户将不胜感激。

除非您需要详细控制下载过程，否则请考虑使用DownloadManager（3），因为它已经处理了上面列出的大多数项目。

但也要考虑您的需求可能会发生变化。例如，DownloadManager does no response caching。它会盲目地多次下载同一个大文件。事后没有简单的方法来解决它。如果您从基本HttpURLConnection（1,2）开始，那么您只需要添加HttpResponseCache。因此，学习基本标准工具的初步努力可能是一项很好的投资。

  

此类在API级别26中已弃用.ProgressDialog是一种模式   对话框，阻止用户与应用程序交互。代替   使用这个类，你应该使用像这样的进度指示器   ProgressBar，可以嵌入到您应用的UI中。或者，   您可以使用通知来通知用户任务的进度。有关详细信息Link

Answer 2

如果您要从互联网上下载内容，请不要忘记为您的清单文件添加权限！

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.helloandroid"
    android:versionCode="1"
    android:versionName="1.0">

        <uses-sdk android:minSdkVersion="10" />

        <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
        <uses-permission android:name="android.permission.INTERNET"></uses-permission>
        <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
        <uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>

        <application 
            android:icon="@drawable/icon" 
            android:label="@string/app_name" 
            android:debuggable="true">

        </application>

</manifest>

Answer 3

是的，上面的代码可以使用。但是，如果您要更新progressbar onProgressUpdate Asynctask中AsyncTask并按下后退按钮或完成您的活动OnResume()则会失去其跟踪功能使用您的UI。当您返回到您的活动时，即使下载正在后台运行，您也会看到进度条上没有更新。因此，在runOnUIThread上尝试使用计时器任务运行类似progressbar的线程，该任务会使用AsyncTask正在运行的背景更新值来更新您的private void updateProgressBar(){ Runnable runnable = new updateProgress(); background = new Thread(runnable); background.start(); } public class updateProgress implements Runnable { public void run() { while(Thread.currentThread()==background) //while (!Thread.currentThread().isInterrupted()) { try { Thread.sleep(1000); Message msg = new Message(); progress = getProgressPercentage(); handler.sendMessage(msg); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } catch (Exception e) { } } } private Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { progress.setProgress(msg.what); } }; 。

private void destroyRunningThreads() {
    if (background != null) {
        background.interrupt();
        background=null;
    }
}

当您的活动不可见时，不要忘记销毁线程。

{{1}}

Answer 4

我建议您使用我的项目Netroid，它基于Volley。我添加了一些功能，如多事件回调，文件下载管理。这可能会有所帮助。

Answer 5

我修改了AsyncTask类来处理同一上下文中progressDialog的创建。我认为以下代码将更具可重用性。 （可以从任何活动中调用它只传递上下文，目标文件，对话框消息）

public static class DownloadTask extends AsyncTask<String, Integer, String> {
    private ProgressDialog mPDialog;
    private Context mContext;
    private PowerManager.WakeLock mWakeLock;
    private File mTargetFile;
    //Constructor parameters :
    // @context (current Activity)
    // @targetFile (File object to write,it will be overwritten if exist)
    // @dialogMessage (message of the ProgresDialog)
    public DownloadTask(Context context,File targetFile,String dialogMessage) {
        this.mContext = context;
        this.mTargetFile = targetFile;
        mPDialog = new ProgressDialog(context);

        mPDialog.setMessage(dialogMessage);
        mPDialog.setIndeterminate(true);
        mPDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        mPDialog.setCancelable(true);
        // reference to instance to use inside listener
        final DownloadTask me = this;
        mPDialog.setOnCancelListener(new DialogInterface.OnCancelListener() {
            @Override
            public void onCancel(DialogInterface dialog) {
                me.cancel(true);
            }
        });
        Log.i("DownloadTask","Constructor done");
    }

    @Override
    protected String doInBackground(String... sUrl) {
        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(sUrl[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();

            // expect HTTP 200 OK, so we don't mistakenly save error report
            // instead of the file
            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                return "Server returned HTTP " + connection.getResponseCode()
                        + " " + connection.getResponseMessage();
            }
            Log.i("DownloadTask","Response " + connection.getResponseCode());

            // this will be useful to display download percentage
            // might be -1: server did not report the length
            int fileLength = connection.getContentLength();

            // download the file
            input = connection.getInputStream();
            output = new FileOutputStream(mTargetFile,false);

            byte data[] = new byte[4096];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1) {
                // allow canceling with back button
                if (isCancelled()) {
                    Log.i("DownloadTask","Cancelled");
                    input.close();
                    return null;
                }
                total += count;
                // publishing the progress....
                if (fileLength > 0) // only if total length is known
                    publishProgress((int) (total * 100 / fileLength));
                output.write(data, 0, count);
            }
        } catch (Exception e) {
            return e.toString();
        } finally {
            try {
                if (output != null)
                    output.close();
                if (input != null)
                    input.close();
            } catch (IOException ignored) {
            }

            if (connection != null)
                connection.disconnect();
        }
        return null;
    }
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // take CPU lock to prevent CPU from going off if the user
        // presses the power button during download
        PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
        mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
                getClass().getName());
        mWakeLock.acquire();

        mPDialog.show();

    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        super.onProgressUpdate(progress);
        // if we get here, length is known, now set indeterminate to false
        mPDialog.setIndeterminate(false);
        mPDialog.setMax(100);
        mPDialog.setProgress(progress[0]);

    }

    @Override
    protected void onPostExecute(String result) {
        Log.i("DownloadTask", "Work Done! PostExecute");
        mWakeLock.release();
        mPDialog.dismiss();
        if (result != null)
            Toast.makeText(mContext,"Download error: "+result, Toast.LENGTH_LONG).show();
        else
            Toast.makeText(mContext,"File Downloaded", Toast.LENGTH_SHORT).show();
    }
}

Answer 6

我发现this博客帖子非常有帮助，它使用loopJ下载文件，它只有一个简单的功能，对一些新的android家伙会有所帮助。

Answer 7

不要忘记用 新文件 （“/ mnt / sdcard / ...”）替换“/ sdcard ...”，否则你会得到一个<强> FileNotFoundException异常

Answer 8

当我开始学习android开发时，我了解到ProgressDialog是要走的路。 setProgress ProgressDialog方法可以调用以在文件下载时更新进度级别。

我在许多应用程序中看到的最好的是它们自定义此进度对话框的属性，以便为进度对话框提供比库存版本更好的外观。很好地保持用户参与一些像青蛙，大象或可爱的猫/小狗的动画。在进度对话框中的任何动画都会吸引用户，他们不想长时间等待。

Answer 9

我的个人建议是使用进度对话并在执行前进行构建，或者在OnPreExecute()启动，如果您使用进度对话框的水平进度条，则会经常发布进度。剩下的部分是优化doInBackground的算法。

Answer 10

使用Android查询库，确实非常酷。您可以将其更改为使用ProgressDialog，如其他示例中所示，此示例将显示布局中的进度视图并在完成后隐藏它。

File target = new File(new File(Environment.getExternalStorageDirectory(), "ApplicationName"), "tmp.pdf");
new AQuery(this).progress(R.id.progress_view).download(_competition.qualificationScoreCardsPdf(), target, new AjaxCallback<File>() {
    public void callback(String url, File file, AjaxStatus status) {
        if (file != null) {
            // do something with file  
        } 
    }
});

Answer 11

您可以使用LiveData和协程观察下载管理器的进度，请参见以下要点

https://gist.github.com/FhdAlotaibi/678eb1f4fa94475daf74ac491874fc0e

data class DownloadItem(val bytesDownloadedSoFar: Long = -1, val totalSizeBytes: Long = -1, val status: Int)

class DownloadProgressLiveData(private val application: Application, private val requestId: Long) : LiveData<DownloadItem>(), CoroutineScope {

    private val downloadManager by lazy {
        application.getSystemService(Context.DOWNLOAD_SERVICE) as DownloadManager
    }

    private val job = Job()

    override val coroutineContext: CoroutineContext
        get() = Dispatchers.IO + job

    override fun onActive() {
        super.onActive()
        launch {
            while (isActive) {
                val query = DownloadManager.Query().setFilterById(requestId)
                val cursor = downloadManager.query(query)
                if (cursor.moveToFirst()) {
                    val status = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_STATUS))
                    Timber.d("Status $status")
                    when (status) {
                        DownloadManager.STATUS_SUCCESSFUL,
                        DownloadManager.STATUS_PENDING,
                        DownloadManager.STATUS_FAILED,
                        DownloadManager.STATUS_PAUSED -> postValue(DownloadItem(status = status))
                        else -> {
                            val bytesDownloadedSoFar = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR))
                            val totalSizeBytes = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_TOTAL_SIZE_BYTES))
                            postValue(DownloadItem(bytesDownloadedSoFar.toLong(), totalSizeBytes.toLong(), status))
                        }
                    }
                    if (status == DownloadManager.STATUS_SUCCESSFUL || status == DownloadManager.STATUS_FAILED)
                        cancel()
                } else {
                    postValue(DownloadItem(status = DownloadManager.STATUS_FAILED))
                    cancel()
                }
                cursor.close()
                delay(300)
            }
        }
    }

    override fun onInactive() {
        super.onInactive()
        job.cancel()
    }

}

Answer 12

我们可以使用协程和工作管理器在Kotlin中下载文件。

在build.gradle中添加依赖项

byte[] cprAsByteArray = aBlob.getBytes((long) 1, (int) aBlob.length());

WorkManager类

    implementation "androidx.work:work-runtime-ktx:2.3.0-beta01"
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.1"

通过活动类别中的工作管理器开始下载

    import android.content.Context
    import android.os.Environment
    import androidx.work.CoroutineWorker
    import androidx.work.WorkerParameters
    import androidx.work.workDataOf
    import com.sa.chat.utils.Const.BASE_URL_IMAGE
    import com.sa.chat.utils.Constants
    import kotlinx.coroutines.delay
    import java.io.BufferedInputStream
    import java.io.File
    import java.io.FileOutputStream
    import java.net.URL

    class DownloadMediaWorkManager(appContext: Context, workerParams: WorkerParameters)
        : CoroutineWorker(appContext, workerParams) {

        companion object {
            const val WORK_TYPE = "WORK_TYPE"
            const val WORK_IN_PROGRESS = "WORK_IN_PROGRESS"
            const val WORK_PROGRESS_VALUE = "WORK_PROGRESS_VALUE"
        }

        override suspend fun doWork(): Result {

            val imageUrl = inputData.getString(Constants.WORK_DATA_MEDIA_URL)
            val imagePath = downloadMediaFromURL(imageUrl)

            return if (!imagePath.isNullOrEmpty()) {
                Result.success(workDataOf(Constants.WORK_DATA_MEDIA_URL to imagePath))
            } else {
                Result.failure()
            }
        }

        private suspend fun downloadMediaFromURL(imageUrl: String?): String? {

            val file = File(
                    getRootFile().path,
                    "IMG_${System.currentTimeMillis()}.jpeg"
            )

            val url = URL(BASE_URL_IMAGE + imageUrl)
            val connection = url.openConnection()
            connection.connect()

            val lengthOfFile = connection.contentLength
            // download the file
            val input = BufferedInputStream(url.openStream(), 8192)
            // Output stream
            val output = FileOutputStream(file)

            val data = ByteArray(1024)
            var total: Long = 0
            var last = 0

            while (true) {

                val count = input.read(data)
                if (count == -1) break
                total += count.toLong()

                val progress = (total * 100 / lengthOfFile).toInt()

                if (progress % 10 == 0) {
                    if (last != progress) {
                        setProgress(workDataOf(WORK_TYPE to WORK_IN_PROGRESS,
                                WORK_PROGRESS_VALUE to progress))
                    }
                    last = progress
                    delay(50)
                }
                output.write(data, 0, count)
            }

            output.flush()
            output.close()
            input.close()

            return file.path

        }

        private fun getRootFile(): File {

            val rootDir = File(Environment.getExternalStorageDirectory().absolutePath + "/AppName")

            if (!rootDir.exists()) {
                rootDir.mkdir()
            }

            val dir = File("$rootDir/${Constants.IMAGE_FOLDER}/")

            if (!dir.exists()) {
                dir.mkdir()
            }
            return File(dir.absolutePath)
        }
    }

Answer 13

<强>权限

  <uses-permission android:name="android.permission.INTERNET" />
  <uses-permission 
   android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

使用 HttpURLConnection

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import android.app.Activity;
import android.app.Dialog;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.Window;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class DownloadFileUseHttpURLConnection extends Activity {

ProgressBar pb;
Dialog dialog;
int downloadedSize = 0;
int totalSize = 0;
TextView cur_val;
String dwnload_file_path =  
"http://coderzheaven.com/sample_folder/sample_file.png";
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button b = (Button) findViewById(R.id.b1);
    b.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
             showProgress(dwnload_file_path);

                new Thread(new Runnable() {
                    public void run() {
                         downloadFile();
                    }
                  }).start();
        }
    });
}

void downloadFile(){

    try {
        URL url = new URL(dwnload_file_path);
        HttpURLConnection urlConnection = (HttpURLConnection)   
 url.openConnection();

        urlConnection.setRequestMethod("GET");
        urlConnection.setDoOutput(true);

        //connect
        urlConnection.connect();

        //set the path where we want to save the file           
        File SDCardRoot = Environment.getExternalStorageDirectory(); 
        //create a new file, to save the downloaded file 
        File file = new File(SDCardRoot,"downloaded_file.png");

        FileOutputStream fileOutput = new FileOutputStream(file);

        //Stream used for reading the data from the internet
        InputStream inputStream = urlConnection.getInputStream();

        //this is the total size of the file which we are downloading
        totalSize = urlConnection.getContentLength();

        runOnUiThread(new Runnable() {
            public void run() {
                pb.setMax(totalSize);
            }               
        });

        //create a buffer...
        byte[] buffer = new byte[1024];
        int bufferLength = 0;

        while ( (bufferLength = inputStream.read(buffer)) > 0 ) {
            fileOutput.write(buffer, 0, bufferLength);
            downloadedSize += bufferLength;
            // update the progressbar //
            runOnUiThread(new Runnable() {
                public void run() {
                    pb.setProgress(downloadedSize);
                    float per = ((float)downloadedSize/totalSize) *     
                    100;
                    cur_val.setText("Downloaded " + downloadedSize +  

                    "KB / " + totalSize + "KB (" + (int)per + "%)" );
                }
            });
        }
        //close the output stream when complete //
        fileOutput.close();
        runOnUiThread(new Runnable() {
            public void run() {
                // pb.dismiss(); // if you want close it..
            }
        });         

    } catch (final MalformedURLException e) {
        showError("Error : MalformedURLException " + e);        
        e.printStackTrace();
    } catch (final IOException e) {
        showError("Error : IOException " + e);          
        e.printStackTrace();
    }
    catch (final Exception e) {
        showError("Error : Please check your internet connection " +  
e);
    }       
}

void showError(final String err){
    runOnUiThread(new Runnable() {
        public void run() {
            Toast.makeText(DownloadFileDemo1.this, err,  
      Toast.LENGTH_LONG).show();
        }
    });
}

void showProgress(String file_path){
    dialog = new Dialog(DownloadFileDemo1.this);
    dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
    dialog.setContentView(R.layout.myprogressdialog);
    dialog.setTitle("Download Progress");

    TextView text = (TextView) dialog.findViewById(R.id.tv1);
    text.setText("Downloading file from ... " + file_path);
    cur_val = (TextView) dialog.findViewById(R.id.cur_pg_tv);
    cur_val.setText("Starting download...");
    dialog.show();

     pb = (ProgressBar)dialog.findViewById(R.id.progress_bar);
     pb.setProgress(0);
            pb.setProgressDrawable(
      getResources().getDrawable(R.drawable.green_progress));  
  }
}

Answer 14

我正在为我现在使用的其他解决方案添加另一个答案，因为Android Query非常庞大且无法维护以保持健康。所以我转到了https://github.com/amitshekhariitbhu/Fast-Android-Networking。

    AndroidNetworking.download(url,dirPath,fileName).build()
      .setDownloadProgressListener(new DownloadProgressListener() {
        public void onProgress(long bytesDownloaded, long totalBytes) {
            bar.setMax((int) totalBytes);
            bar.setProgress((int) bytesDownloaded);
        }
    }).startDownload(new DownloadListener() {
        public void onDownloadComplete() {
            ...
        }

        public void onError(ANError error) {
            ...
        }
    });

Answer 15

重要

AsyncTask在Android 11中已弃用。

有关更多信息，请查看以下帖子

• Android AsyncTask API deprecating in Android 11.What are the alternatives?
• https://developer.android.com/reference/android/os/AsyncTask

可能应该按照Google的建议移至Concorency Framework

Answer 16

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

        private PowerManager.WakeLock mWakeLock;
        String onlinePathBundle, onlinePathMusic, offlinePathBundle, offlinePathMusic;

        CircleProgressBar progressBar;
        RelativeLayout rl_progress;
        ImageView btn_download;
        TextView tv_progress;

        public DownloadTask(String onlinePathBundle, String onlinePathMusic, String offlinePathBundle, String offlinePathMusic, CircleProgressBar progressBar, RelativeLayout rl_progress, ImageView btn_download,
                            TextView tv_progress) {
            this.offlinePathBundle = offlinePathBundle;
            this.offlinePathMusic = offlinePathMusic;
            this.progressBar = progressBar;
            this.rl_progress = rl_progress;
            this.btn_download = btn_download;
            this.tv_progress = tv_progress;
            this.onlinePathBundle = onlinePathBundle;
            this.onlinePathMusic = onlinePathMusic;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            progressBar.setMax(100);
            rl_progress.setVisibility(View.VISIBLE);
            btn_download.setVisibility(View.GONE);

            PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
            mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, getClass().getName());
            mWakeLock.acquire();
        }

        @Override
        protected String doInBackground(String... sUrl) {
            String firstResult = downTask(onlinePathBundle, 1, offlinePathBundle);
            String seondResult = downTask(onlinePathMusic, 2, offlinePathMusic);
            if (firstResult != null) {
                Toast.makeText(SplashActivity.this, "Download error: " + firstResult, Toast.LENGTH_LONG).show();
                return firstResult;
            } else {
                return seondResult;
            }

        }

        @Override
        protected void onProgressUpdate(Integer... progress) {
            super.onProgressUpdate(progress);
            progressBar.setProgress(progress[0]);
            tv_progress.setText(progress[0] + "%");

        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            rl_progress.setVisibility(View.GONE);
            btn_download.setVisibility(View.VISIBLE);
            if (result != null) {
                Toast.makeText(SplashActivity.this, "Download error: " + result, Toast.LENGTH_LONG).show();
            } else {
                rl_progress.setVisibility(View.GONE);
                btn_download.setVisibility(View.GONE);
            }

        }

        public String downTask(String onlineNewPath, int numberOfTask, String offlineNewPath) {
            InputStream input = null;
            OutputStream output = null;
            HttpURLConnection connection = null;
            try {
                URL url = new URL(onlineNewPath);
                connection = (HttpURLConnection) url.openConnection();
                connection.connect();

                // expect HTTP 200 OK, so we don't mistakenly save error report
                // instead of the file
                if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                    return "Server returned HTTP " + connection.getResponseCode()
                            + " " + connection.getResponseMessage();
                }

                // this will be useful to display download percentage
                // might be -1: server did not report the length
                int fileLength = connection.getContentLength();

                // download the file
                input = connection.getInputStream();
                output = new FileOutputStream(offlineNewPath);

                byte data[] = new byte[4096];
                long total = 0;
                int count;
                while ((count = input.read(data)) != -1) {
                    // allow canceling with back button
                    if (isCancelled()) {
                        input.close();
                        return null;
                    }
                    total += count;
                    // publishing the progress....
                    if (fileLength > 0) {// only if total length is known
                        if (numberOfTask == 1) {
                            publishProgress((int) (total * 50 / fileLength));
                        } else if (numberOfTask == 2) {
                            publishProgress(((int) (total * 50 / fileLength)) + 50);
                        }

                    }
                    output.write(data, 0, count);
                }
            } catch (Exception e) {
                return e.toString();
            } finally {
                try {
                    if (output != null)
                        output.close();
                    if (input != null)
                        input.close();
                } catch (IOException ignored) {
                }

                if (connection != null)
                    connection.disconnect();
            }
            return null;
        }
    }