WebView中无法下载问题解决方法

WebView 中无法下载的问题一般是因为没有设置相应的下载配置，可以尝试以下解决方法：

1. 在 AndroidManifest.xml 中添加权限：

   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

2. 设置 WebChromeClient，并重写 onDownloadStart 方法：

   WebView webView = findViewById(R.id.webView);
   webView.setWebChromeClient(new WebChromeClient() {
       @Override
       public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimetype, long contentLength) {
           DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
           request.setMimeType(mimetype);
           String cookies = CookieManager.getInstance().getCookie(url);
           request.addRequestHeader("cookie", cookies);
           request.addRequestHeader("User-Agent", userAgent);
           request.setDescription("Downloading file...");
           request.setTitle(URLUtil.guessFileName(url, contentDisposition, mimetype));
           request.allowScanningByMediaScanner();
           request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
           request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, URLUtil.guessFileName(url, contentDisposition, mimetype));
           DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
           dm.enqueue(request);
           Toast.makeText(getApplicationContext(), "Downloading File", Toast.LENGTH_LONG).show();
       }
   });

重写 onDownloadStart 方法后，点击 WebView 中的下载链接时，会调用该方法进行下载。

注意：需要在 AndroidManifest.xml 中添加 DOWNLOAD_SERVICE 权限。

<uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION" />