与Android下载一个文件，并显示在一个ProgressDialog进展 [英] Download a file with Android, and showing the progress in a ProgressDialog
问题描述
我想编写得到更新的简单应用程序。为此，我需要一个简单的功能，可以下载一个文件和显示在 ProgressDialog 目前的进展的。我知道该怎么做了 ProgressDialog ，但我不知道如何显示目前的进展以及如何下载的文件摆在首位。
I am trying to write a simple application that gets updated. For this I need a simple function that can download a file and show the current progress in a ProgressDialog. I know how to do the ProgressDialog, but I'm not sure how to display the current progress and how to download the file in the first place.
推荐答案
有很多方法来下载文件。下面我会后最常见的方式;它是由你来决定哪种方法是为你的应用程序更好。
There are many ways to download files. Following I will post most common ways; it is up to you to decide which method is better for your app.
此方法将允许您执行一些后台进程和更新，同时用户界面（在这种情况下，我们将更新进度条）。
This method will allow you to execute some background processes and update the UI at the same time (in this case, we'll update a progress bar).
这是一个例子code：
This is an example code:
// 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);
}
});
在的AsyncTask 将是这样的：
// 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;
}
以上（ doInBackground ）的方法在后台线程始终运行。你不应该做任何UI任务那里。在另一方面， onProgressUpdate 和在preExecute 运行在UI线程，所以你可以改变进度条：
The method above (doInBackground) runs always on a background thread. You shouldn't do any UI tasks there. On the other hand, the onProgressUpdate and onPreExecute run on the UI thread, so there you can change the progress bar:
@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();
}
有关此运行，你需要的WAKE_LOCK权限。
For this to run, you need the WAKE_LOCK permission.
<uses-permission android:name="android.permission.WAKE_LOCK" />
2。下载从服务
这里的大问题是：？如何更新从服务我的活动的。在下面的例子中，我们将使用两个类，你可能不知道的： ResultReceiver 和 IntentService 。 ResultReceiver 是一个可以让我们从一个服务更新我们的线程; IntentService 是服务这产生一个线程来执行从那里工作背景的子类（你应该知道，一个服务实际运行在你的应用程序在同一个线程，当你伸出服务，你必须手动产卵运行CPU阻止新主题操作）。
2. Download from Service
The big question here is: how do I update my activity from a service?. In the next example we are going to use two classes you may not be aware of: ResultReceiver and IntentService. ResultReceiver is the one that will allow us to update our thread from a service; IntentService is a subclass of Service which spawns a thread to do background work from there (you should know that a Service runs actually in the same thread of your app; when you extends Service, you must manually spawn new threads to run CPU blocking operations).
下载服务可以是这样的：
Download service can look like this:
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 {
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());
OutputStream output = new FileOutputStream("/sdcard/BarcodeScanner-debug.apk");
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);
}
output.flush();
output.close();
input.close();
} catch (IOException e) {
e.printStackTrace();
}
Bundle resultData = new Bundle();
resultData.putInt("progress" ,100);
receiver.send(UPDATE_PROGRESS, resultData);
}
}
添加服务到您的清单：
Add the service to your manifest:
<service android:name=".DownloadService"/>
和活动将是这样的：
// 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);
这是为 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");
mProgressDialog.setProgress(progress);
if (progress == 100) {
mProgressDialog.dismiss();
}
}
}
}
2.1使用Groundy库
Groundy 是一个库，基本上可以帮助你在后台运行的code片服务，它是基于上面的 ResultReceiver 的概念。这个库是德precated 的时刻。这是怎样的全 code看起来像：
2.1 Use Groundy library
Groundy is a library that basically helps you run pieces of code in a background service, and it is based on the ResultReceiver concept shown above. This library is deprecated at the moment. This is how the whole code would look like:
在这里你都显示在对话框的活动......
The activity where you are showing the dialog...
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;
}
}
};
}
A GroundyTask 用于实施 Groundy 以下载文件并显示进度：
A GroundyTask implementation used by Groundy to download the file and show the progress:
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;
}
}
}
和只添加这清单：
<service android:name="com.codeslap.groundy.GroundyService"/>
这再简单不过了，我认为。随意在Github上最新的罐子，你准备好了。请记住， Groundy 的主要目的是在后台服务和后期结果来调用外部的REST API的用户界面与轻松。如果你正在做类似的东西在你的应用程序，它可以是非常有用的。
It couldn't be easier I think. Just grab the latest jar from Github and you are ready to go. Keep in mind that Groundy's main purpose is to make calls to external REST apis in a background service and post results to the UI with easily. If you are doing something like that in your app, it could be really useful.
此方法是真棒，你不必担心下载的文件中手动，处理线程，流等姜饼带来了一个新功能：下载管理器，它允许你轻松下载文件，并委托拼搏到系统中。
This method is awesome, you do not have to worry about downloading the file manually, handle threads, streams, etc. GingerBread brought a new feature: DownloadManager which allows you to download files easily and delegate the hard work to the system.
首先，让我们来看看一个实用的方法：
First, let's see a utility method:
/**
* @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;
}
方法的名称解释这一切。一旦确定下载管理器是可用的，你可以做这样的事情：
Method's name explains it all. Once you are sure DownloadManager is available, you can do something like this:
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。
Download progress will be showing in the notification bar.
第一和第二种方法是冰山的一角。有很多事情你必须要记住，如果你想你的应用程序保持强劲。这里是一个简短的清单：
First and second methods are just the tip of the iceberg. There are lots of things you have to keep in mind if you want your app to be robust. Here is a brief list:
- 您必须检查用户是否有互联网连接可用
- 确保你有正确的权限（
网络和WRITE_EXTERNAL_STORAGE）;也ACCESS_NETWORK_STATE如果您要检查网络的可用性。 - 确保该目录是您要下载的文件存在，并且具有写权限。
- 如果下载过大，你可能要实现的方式来恢复下载，如果previous尝试都失败了。
- 在用户将，如果你让他们中断下载不胜感激。
- You must check whether user has an internet connection available
- Make sure you have the right permissions (
INTERNETandWRITE_EXTERNAL_STORAGE); alsoACCESS_NETWORK_STATEif you want to check internet availability. - Make sure the directory were you are going to download files exist and has write permissions.
- If download is too big you may want to implement a way to resume the download if previous attempts failed.
- Users will be grateful if you allow them to interrupt the download.
除非你想完全控制在下载过程中，我强烈建议使用下载管理器这已经处理大部分上面列出的项目。
Unless you want to have full control over the download process, I highly recommend using DownloadManager which already handles most of the items listed above.
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