Android WebView应用下载PDF后如何实现自动打开功能？

现有代码无需大改，仅需补充下载完成监听和调用系统打开PDF的逻辑即可实现需求，完全复用现有从站点获取原始文件名的规则，不需要你自定义文件名。

修改步骤 #

1. 补充成员变量 #

在WebViewActivity类中增加以下成员变量：

// 存储当前PDF下载任务的ID，用于匹配下载完成广播
private long curPdfDownloadId;
// 存储本次下载的PDF原始文件名
private String curPdfFileName;
// 监听下载完成的广播接收器
private BroadcastReceiver downloadCompleteReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(intent.getAction())) {
            long completeId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
            if (completeId == curPdfDownloadId) {
                openDownloadedPdf();
            }
        }
    }
};

2. 修改下载监听逻辑 #

调整原有setDownloadListener内的代码，保存下载任务ID和文件名：

webView.setDownloadListener(new DownloadListener() {
    @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);
        String fileName = URLUtil.guessFileName(url,contentDisposition,mimeType);
        request.setDescription("Downloading File");
        request.setTitle(fileName);
        request.allowScanningByMediaScanner();
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
        request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, fileName);
        DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
        
        // 仅PDF文件增加自动打开逻辑，其他文件走原有下载逻辑
        if ("application/pdf".equals(mimeType)) {
            curPdfFileName = fileName;
            curPdfDownloadId = downloadManager.enqueue(request);
            Toast.makeText(getApplicationContext(), "PDF下载中，完成后将自动打开", Toast.LENGTH_SHORT).show();
        } else {
            downloadManager.enqueue(request);
            Toast.makeText(getApplicationContext(), "Downloading File", Toast.LENGTH_SHORT).show();
        }
    }
});

3. 新增PDF打开方法 #

在WebViewActivity中新增打开PDF的工具方法，适配不同Android版本权限要求：

private void openDownloadedPdf() {
    File pdfFile = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), curPdfFileName);
    Uri pdfUri;
    // 适配Android 7.0及以上的文件访问权限
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
        pdfUri = FileProvider.getUriForFile(this, getPackageName() + ".fileprovider", pdfFile);
    } else {
        pdfUri = Uri.fromFile(pdfFile);
    }
    Intent openIntent = new Intent(Intent.ACTION_VIEW);
    openIntent.setDataAndType(pdfUri, "application/pdf");
    openIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    openIntent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
    try {
        startActivity(openIntent);
    } catch (ActivityNotFoundException e) {
        Toast.makeText(this, "未找到可用的PDF阅读器，请先安装", Toast.LENGTH_SHORT).show();
    }
}

4. 注册/注销下载完成广播 #

调整原有onStart和onStop方法，注册和注销下载监听广播：

@Override
protected void onStart() {
    IntentFilter filter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
    registerReceiver(networkChangeListener, filter);
    // 新增注册下载完成广播
    IntentFilter downloadFilter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE);
    registerReceiver(downloadCompleteReceiver, downloadFilter);
    super.onStart();
}

@Override
protected void onStop() {
    unregisterReceiver(networkChangeListener);
    // 新增注销下载完成广播
    unregisterReceiver(downloadCompleteReceiver);
    super.onStop();
}

5. 配置FileProvider（Android 7.0+必需） #

1. 在res/xml目录下新建file_paths.xml文件，内容如下：

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path name="downloads" path="Download/" />
</paths>

2. 在AndroidManifest.xml的application标签内添加Provider配置：

<provider
    android:name="androidx.core.content.FileProvider"
    android:authorities="${applicationId}.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths" />
</provider>

注意说明 #

• 不需要你集成内置PDF阅读器，直接调用系统已安装的第三方PDF应用打开即可
• 如果你需要所有下载文件都自动打开，去掉下载逻辑里的mimeType判断即可
• 无PDF阅读器时会弹出提示，不会导致应用崩溃

内容的提问来源于stack exchange，提问作者Gedanggoreng