Android Xamarin：基于存储路径打开各类文件的实现需求

Hey there! Let's figure out how to make your app prompt users to choose an external app for .docx, .xlsx, and other non-PDF files, while keeping your existing WebView PDF handling intact. Here's a step-by-step solution tailored to common mobile development frameworks (I'll cover Android and iOS examples since those are the most common targets):

Start by extending your existing file type check. We'll keep the PDF WebView flow and add a new branch for other file types to trigger the system's app chooser:

var fileType = path.Split('.').Last().ToLower();
if (fileType == "pdf")
{
    // Keep your existing WebView PDF opening logic here
    LoadPdfInWebView(path);
}
else
{
    // Trigger system app chooser for .docx, .xlsx, etc.
    OpenFileWithSystemChooser(path);
}

Android Implementation #

On Android, we'll use an Intent.ACTION_VIEW to let the system handle file opening, and use FileProvider (required for Android 7.0+) to avoid security exceptions when sharing file URIs.

1. Add the App Chooser Method #

private void OpenFileWithSystemChooser(string filePath)
{
    var targetFile = new Java.IO.File(filePath);
    // Get a secure content URI using FileProvider
    var fileUri = Android.Support.V4.Content.FileProvider.GetUriForFile(
        this,
        $"{PackageName}.fileprovider", // Match your provider authority in AndroidManifest
        targetFile);

    // Create the intent to view the file
    var openIntent = new Intent(Intent.ActionView);
    openIntent.SetDataAndType(fileUri, GetFileMimeType(filePath));
    openIntent.AddFlags(ActivityFlags.GrantReadUriPermission); // Grant access to the app that opens the file
    openIntent.AddFlags(ActivityFlags.NewTask);

    // Show the app chooser dialog
    var chooser = Intent.CreateChooser(openIntent, "Select an app to open this file");
    StartActivity(chooser);
}

// Helper to get the correct MIME type for the file
private string GetFileMimeType(string filePath)
{
    var defaultMime = "application/octet-stream";
    var fileExtension = Path.GetExtension(filePath).TrimStart('.').ToLower();
    
    var mimeMap = MimeTypeMap.Singleton;
    var mappedMime = mimeMap.GetMimeTypeFromExtension(fileExtension);
    
    return string.IsNullOrEmpty(mappedMime) ? defaultMime : mappedMime;
}

2. Configure FileProvider in AndroidManifest.xml #

Add this provider entry inside the <application> tag to enable secure URI sharing:

<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>

3. Create the File Paths Configuration #

Create a res/xml/file_paths.xml file to define which directories your app can share files from (adjust the path to match where you store downloaded files):

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- Use external-files-path for files stored in your app's external files directory -->
    <external-files-path name="downloaded_files" path="." />
    <!-- Use files-path for app-internal storage, or external-cache-path for cache files -->
</paths>

iOS Implementation #

On iOS, we'll use UIDocumentInteractionController to present the system's app chooser and preview options.

Add the App Chooser Method #

private void OpenFileWithSystemChooser(string filePath)
{
    var fileUrl = NSUrl.FromFilename(filePath);
    var docController = UIDocumentInteractionController.FromUrl(fileUrl);
    
    // Set a delegate to handle preview interactions
    docController.Delegate = new DocumentInteractionDelegate(this);
    
    // Present the app chooser menu
    docController.PresentOptionsMenu(View.Frame, View, true);
}

// Delegate class to support preview functionality
public class DocumentInteractionDelegate : UIDocumentInteractionControllerDelegate
{
    private readonly UIViewController _hostViewController;
    
    public DocumentInteractionDelegate(UIViewController host)
    {
        _hostViewController = host;
    }
    
    public override UIViewController ViewControllerForPreview(UIDocumentInteractionController controller)
    {
        return _hostViewController;
    }
    
    public override UIView ViewForPreview(UIDocumentInteractionController controller)
    {
        return _hostViewController.View;
    }
}

• Permissions: Ensure your app has the necessary storage permissions:
  • Android: Request READ_EXTERNAL_STORAGE (for Android 10 and below) or use scoped storage practices for Android 11+.
  • iOS: Add usage descriptions in Info.plist (e.g., NSDocumentsFolderUsageDescription) if accessing user-facing storage.
• MIME Types: The GetFileMimeType helper ensures the system knows what kind of file it's handling, which helps find the right apps to open it.
• Scoped Storage (Android 11+): If you're targeting Android 11 or higher, avoid direct file paths where possible—use MediaStore or Storage Access Framework (SAF) for better compatibility.

内容的提问来源于stack exchange，提问作者Aiko West