从Android应用程序下载文件时出现问题

Question

有必要通过应用程序从web服务器下载文件，但文件没有加载，这是我正在使用的代码：

manager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
Uri uri = Uri.parse("https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf");
DownloadManager.Request request = new DownloadManager.Request(uri);
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);
long reference = manager.enqueue(request);

在清单中，我有以下权限：

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.WAKE_LOCK"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.ACCESS_DOWNLOAD_MANAGER"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.REQUEST_INSTALL_PACKAGES"/>
<uses-permission android:name="android.permission.REQUEST_DELETE_PACKAGES"/>

文件是在设备上创建的，但标记是"；在队列中"；没有发生任何进一步的事情。

如果你只是按照浏览器中的链接，那么下载就不会出现问题。

通过设置，还可以检查对设备内存的访问。

我哪里错了？

Answer 1

请尝试这类代码的方式，这可能会帮助您

public class DownloadHelper {
private long downloadReference = 0
private DownloadManager downloadManager;
DownloadCompleteListener completeListener= null;

public interface DownloadCompleteListener{
void ondownloadComplete(String name,String path,Uri uri);
void ondownloadFailled(String error);
}

private BroadcastReceiver receiver = new BroadcastReceiver () {

@Override
void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (action == DownloadManager.ACTION_DOWNLOAD_COMPLETE) {
long downloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
if (downloadId != downloadReference) {
context.unregisterReceiver(this);
return;
}
DownloadManager.Query query = new DownloadManager.Query();
query.setFilterById(downloadReference);
Cursor cursor = downloadManager.query(query);
if(cursor != null){
if (cursor.moveToFirst()) {
int columnIndex = cursor.getColumnIndex(DownloadManager.COLUMN_STATUS);
if (DownloadManager.STATUS_SUCCESSFUL == cursor.getInt(columnIndex)) {
String localFile = cursor.getString(cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI));
String localName = localFile.substring(localFile.lastIndexOf("/")+1);//cursor.getString(cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_FILENAME))
completeListener.ondownloadComplete(localName,localFile,null);
} else if (DownloadManager.STATUS_FAILED == cursor.getInt(columnIndex)) {
completeListener.ondownloadFailled(cursor.getString(cursor.getColumnIndex(DownloadManager.COLUMN_REASON)));
}
}else{
completeListener.ondownloadFailled("Download cancelled or failled");
}
cursor.close();
}else{
completeListener.ondownloadFailled("Download cancelled or failled");
}
context.unregisterReceiver(this);
}
}
};
public String getallreadyfile(String name){
return Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
.getAbsolutePath().toString() + "/" + name;
}
public void downloadFile(Context context,String url,String mimeType,DownloadCompleteListener completeListener) {
this.completeListener = completeListener;
String guessFileName = URLUtil.guessFileName(url, null, mimeType);
if(url == null || url.isEmpty()){            
return;
}
String allreadyfile = getallreadyfile(guessFileName);
File applictionFile = new File(allreadyfile);
if(isAllreadyAvailabel(context,applictionFile)){
completeListener.ondownloadComplete(applictionFile.getName(),applictionFile.getAbsolutePath(),null);
return
}
downloadManager = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
Uri downloadUri = Uri.parse(url);
DownloadManager.Request request = new DownloadManager.Request(downloadUri);
request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_MOBILE).setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);
//setAllowedOverRoaming(true)
//            setTitle(guessFileName)
//            setDescription(guessFileName)
//            setVisibleInDownloadsUi(true)
request.allowScanningByMediaScanner();
//            setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED)
//request.setDestinationUri(Uri.fromFile(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)))
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, guessFileName);
context.registerReceiver(receiver, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
downloadReference = downloadManager.enqueue(request);
}
public boolean isAllreadyAvailabel(Context context,File applictionFile){
if(applictionFile.canRead() && applictionFile.length()>0) {
return true;
}else{
try {
File file = new File(applictionFile.getAbsolutePath());
if (file.exists()) {
file.delete();
}
} catch (Exception e) {
e.printStackTrace();
}
}
return false;
}
}