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我正在尝试编写一个简单的更新应用程序。为此，我需要一个简单的函数，可以下载文件并在.我知道该怎么做，但我不确定如何显示当前进度以及如何首先下载文件。ProgressDialogProgressDialog
网友回答：
如果您要从互联网下载内容，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>
网友回答：
有很多方法可以下载文件。接下来我将发布最常见的方法;由你决定哪种方法更适合你的应用。
AsyncTask此方法将允许您执行一些后台进程并同时更新 UI（在这种情况下，我们将更新进度条）。
进口：
import android.os.PowerManager;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.FileOutputStream;
import java.net.HttpURLConnection;
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
}
});
将如下所示：AsyncTask
// 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;
}
上面的方法（）始终在后台线程上运行。你不应该在那里执行任何 UI 任务。另一方面，和在UI线程上运行，因此您可以在此处更改进度条：doInBackgroundonProgressUpdateonPreExecute
@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" />
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，我们将使用两个您可能不知道的类：和 。 是允许我们从服务更新线程的那个; 是一个子类，它生成一个线程以从那里执行后台工作（您应该知道 a 实际上在应用程序的同一线程中运行;当您扩展时，您必须手动生成新线程以运行 CPU 阻塞操作）。ResultReceiverIntentServiceResultReceiverIntentServiceServiceServiceService
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);
这是来玩的：ResultReceiver
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();
}
}
}
}
Groundy是一个库，基本上可以帮助你在后台服务中运行代码片段，它基于上面显示的概念。此库目前已弃用。整个代码如下所示：ResultReceiver
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用来下载文件并显示进度的实现：GroundyTask
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;
}
}
}
只需将其添加到清单中：
<service android:name="com.codeslap.groundy.GroundyService"/>
我认为这再简单不过了。只需从Github上拿起最新的罐子，您就可以开始了。请记住，Groundy的主要目的是在后台服务中调用外部REST API，并轻松地将结果发布到UI。如果您在应用程序中执行类似操作，它可能非常有用。
DownloadManagerGingerBreadGingerBread 带来了一项新功能，它使您可以轻松下载文件并委派处理线程、流等的艰苦工作。到系统。DownloadManager
首先，让我们看一个实用工具方法：
/**
* @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。确定可用后，您可以执行以下操作：DownloadManager
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。
第一种方法和第二种方法只是冰山一角。如果您希望您的应用程序强大，则必须记住很多事情。以下是简要列表：
INTERNETWRITE_EXTERNAL_STORAGEACCESS_NETWORK_STATE除非您需要详细控制下载过程，否则请考虑使用 （3），因为它已经处理了上面列出的大多数项目。DownloadManager
但也要考虑到您的需求可能会发生变化。例如，不执行响应缓存。它会多次盲目下载同一个大文件。事后没有简单的方法可以修复它。如果您从基本 （1， 2） 开始，那么您只需要添加一个 .因此，学习基本标准工具的初始努力可能是一项不错的投资。DownloadManagerHttpURLConnectionHttpResponseCache
此类在 API 级别 26 中已弃用。进度对话框是一个模式
对话框，可阻止用户与应用交互。不应使用此类，而
应使用进度条等
进度指示器，该指示器可以嵌入到应用的 UI 中。或者，
您可以使用通知通知用户任务的进度。更多详情链接
网友回答：
是的，上面的代码将起作用.但是，如果您要更新您的 in 并按下后退按钮或完成您的活动，则会失去您的 UI 跟踪。当您返回活动时，即使下载在后台运行，您也不会在进度条上看到任何更新。因此，尝试运行一个线程，就像使用计时器任务一样，该任务使用从运行后台更新的值来更新您的值。progressbaronProgressUpdateAsynctaskAsyncTaskOnResume()runOnUIThreadprogressbarAsyncTask
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);
}
};
不要忘记在您的活动不可见时销毁线程。
private void destroyRunningThreads() {
if (background != null) {
background.interrupt();
background=null;
}
}
模板简介：该模板名称为【使用 Android 下载文件，并在 ProgressDialog 中显示进度】，大小是暂无信息，文档格式为.编程语言，推荐使用Sublime/Dreamweaver/HBuilder打开，作品中的图片，文字等数据均可修改，图片请在作品中选中图片替换即可，文字修改直接点击文字修改即可，您也可以新增或修改作品中的内容，该模板来自用户分享，如有侵权行为请联系网站客服处理。欢迎来懒人模板【Java】栏目查找您需要的精美模板。
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