Android DownloadManager无法在智能手机上运行

Question

目前，我正在使用WebView显示pdf并尝试实现下载功能。 我正在使用下载管理器来做到这一点。 它适用于下载了pdf文件的模拟器。 但是，在智能手机中，它仅显示“下载1个任务”。 几秒钟后，通知消失，没有下载任何内容。 我将在Api 19及更高版本中实现它。 我的智能手机是android 5.1。 这个问题有什么解决办法吗？

PdfFullscreenActivity.java

public class PdfFullscreenActivity extends AppCompatActivity {

public WebView webview;
public String str;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_pdf_fullscreen);

    Intent intent = getIntent();
    str = intent.getExtras().getString("PDF_TAG");

    String url = "https://docs.google.com/viewer?embedded=true&url=https://spmsejarahscore.000webhostapp.com/web/media/pdf/" + str;

    webview = (WebView)findViewById(webView);
    webview.getSettings().setJavaScriptEnabled(true);
    webview.getSettings().setPluginState(WebSettings.PluginState.ON);
    webview.getSettings().setBuiltInZoomControls(false);
    webview.getSettings().setAllowFileAccess(true);
    webview.getSettings().setAppCacheMaxSize(1024 * 1024);
    webview.getSettings().setAppCacheEnabled(true);
    webview.loadUrl(url);

    webview.setWebViewClient(new WebViewClient() {
        public void onPageFinished(WebView view, String url) {
        }

        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            return true;
        }
    });
}

public void onBackPressed(){
    super.onBackPressed();
    finish();
}

public void download(View v){
    // https://spmsejarahscore.000webhostapp.com/web/media/pdf/SijilPelajaranMalaysia(SPM)_2011_P1,2.pdf

    String downloadUrl = "https://spmsejarahscore.000webhostapp.com/web/media/pdf/" + str;

    Uri urifile = Uri.parse(downloadUrl);
    downloadfile(urifile, v);
}

public long downloadfile(Uri uri, View view){
    long downloadReference;
    DownloadManager downloadManager;

    // Create request for android download manager
    downloadManager = (DownloadManager)getSystemService(DOWNLOAD_SERVICE);
    DownloadManager.Request request = new DownloadManager.Request(uri);

    //Setting title of request
    request.setTitle("Downloading");

    //Setting description of request
    request.setDescription(str);

    //Set the local destination for the downloaded file to a path within the application's external files directory
    request.setDestinationInExternalFilesDir(PdfFullscreenActivity.this, Environment.DIRECTORY_DOWNLOADS, str);

    //Enqueue download and save into referenceId
    downloadReference = downloadManager.enqueue(request);

    return downloadReference;
}
}

activity_pdf_fullscreen.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.foong.spmsejerahscore.PdfFullscreenActivity">

<WebView
    android:id="@+id/webView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<ImageButton
    android:id="@+id/downloadbtn"
    android:layout_width="45dp"
    android:layout_height="45dp"
    android:layout_alignParentTop="true"
    android:layout_alignParentRight="true"
    android:layout_marginTop="10dp"
    android:layout_marginRight="10dp"
    android:onClick="download"
    android:background="#264745"
    android:src="@mipmap/ic_download" />

</RelativeLayout>

Answer 1

加：

request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED)