为什么我的下载链接在Android WebView中不起作用？

Question

In my angular 2 application, users can click on a file to download it. This will get a link from an authenticated web service call, and download it in the browser.

It all works fine from a browser (PC, Chrome on Android or whatever).

It doesn't work in an hybrid Android app with a WebView, although I think I did whatever was needed. It seems that WebViewClient::onLoadResource is never called for the generated link.

Here is the relevant part in my angular 2 component:

onPathClicked(path:Path) {
    if (path.directory) {
        var newPathEntries = this.appendToPath(this.pathEntries, path.fileName);
        this.searchContents(newPathEntries);
    } else {
        var fileName = path.fileName;
        var pathEntries = this.pathEntries.push(fileName);
        var fullPath = this.buildFullPath(pathEntries);
        this.fileService.getFileDownloadUrl(fullPath)
            .then((url)=> {
                var fileInput:HTMLAnchorElement = <HTMLAnchorElement>document.getElementById('downloadFileLink');
                fileInput.href = url;
                fileInput.setAttribute('download', path.fileName);
                fileInput.click();
            })
            .catch((error)=> {
                this.errorService.showError('Impossible de télécharger le fichier', error);
            });
    }
}

Here is the android part:

import android.app.Activity;
import android.app.AlertDialog;
import android.app.DownloadManager;
import android.app.DownloadManager.Request;
import android.content.DialogInterface;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.view.Menu;
import android.view.MenuInflater;
import android.webkit.DownloadListener;
import android.webkit.WebChromeClient;
import android.webkit.WebResourceError;
import android.webkit.WebResourceRequest;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

public class BlablaActivity extends Activity {

    private WebView webView;

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

        webView = (WebView) findViewById(R.id.webView);

        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);
        webSettings.setDomStorageEnabled(true);
        webSettings.setDatabaseEnabled(true);

        WebChromeClient webChromeClient = new WebChromeClient() {
        };
        webView.setWebChromeClient(webChromeClient);

        final DownloadListener downloadListener = new DownloadListener() {
            public void onDownloadStart(String url, String userAgent,
                                        String contentDisposition, String mimetype,
                                        long contentLength) {
                Request request = new Request(Uri.parse(url));
                request.allowScanningByMediaScanner();
                request.setNotificationVisibility(Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
                request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "download");

                DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
                downloadManager.enqueue(request);

                Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT); //This is important!
                intent.addCategory(Intent.CATEGORY_OPENABLE); //CATEGORY.OPENABLE
                intent.setType("*/*");//any application,any extension
                Toast.makeText(getApplicationContext(), "Téléchargement", //To notify the Client that the file is being downloaded
                        Toast.LENGTH_LONG).show();
            }
        };
        webView.setDownloadListener(downloadListener);

        WebViewClient webViewClient = new WebViewClient() {
            @Override
            public void onPageStarted(WebView view, String url, Bitmap favicon) {
                super.onPageStarted(view, url, favicon);
            }

            @Override
            public void onLoadResource(WebView view, String url) {
                super.onLoadResource(view, url);
            }

            @Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                view.loadUrl(url);
                webView.setDownloadListener(downloadListener);
                return true;
            }

            @Override
            public void onReceivedError(WebView view, WebResourceRequest request, WebResourceError error) {
//                view.loadUrl("file:///android_asset/load_error.html");
//                view.loadData("Erreur : " + error + ". Veuillez vous connecter pour utiliser l'application.", "text/plain", "utf-8");
                showDefaultError();
            }
        };
        webView.setWebViewClient(webViewClient);

        loadJsApp();
    }

    private void loadJsApp() {
        webView.loadUrl("https://www.mymobileapp.com");
    }

    private void showDefaultError() {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Erreur");
        builder.setMessage("Désolé, une erreur s'est produite. Veuillez vérifier votre connexion Internet.");

        builder.setIcon(android.R.drawable.ic_dialog_alert);

        AlertDialog dialog = builder.create();
        builder.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
                loadJsApp();
            }
        });

        dialog.show();

        //Toast.makeText(this, "Réseau indisponible !", Toast.LENGTH_LONG).show();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.menu.menu_xyz_mobile, menu);
        return true;
    }

}

Answer 1

Strangly enough, the 'download' attribute on an HTML anchor element does not seem to be handled correctly in an Android WebView. Removing that attribute should trigger the file download as expected.