C# .NET MAUI中WebView下载功能失效问题求助

你的问题根源在于.NET MAUI的WebView默认不会自动处理网页中的下载请求，需要针对Android和iOS平台分别添加下载逻辑处理。以下是具体的实现步骤：

1. 为WebView添加平台特定的下载处理 #

Android平台 #

在Android项目中创建自定义WebView Handler，通过设置DownloadListener拦截下载请求：

using Android.Webkit;
using Microsoft.Maui.Handlers;

namespace YourAppName.Platforms.Android;

public class CustomWebViewHandler : WebViewHandler
{
    protected override void ConnectHandler(Android.Webkit.WebView platformView)
    {
        base.ConnectHandler(platformView);
        platformView.SetDownloadListener(new CustomDownloadListener());
    }
}

public class CustomDownloadListener : Java.Lang.Object, IDownloadListener
{
    public void OnDownloadStart(string url, string userAgent, string contentDisposition, string mimetype, long contentLength)
    {
        var request = new Android.App.DownloadManager.Request(Android.Net.Uri.Parse(url));
        request.SetMimeType(mimetype);

        // 自动解析文件名
        var filename = Android.Webkit.URLUtil.GuessFileName(url, contentDisposition, mimetype);
        request.SetTitle(filename);
        request.SetDescription("正在下载文件...");
        request.SetNotificationVisibility(Android.App.DownloadVisibility.VisibleNotifyCompleted);

        // 设置保存到系统下载目录
        var destinationUri = Android.Net.Uri.WithAppendedPath(
            Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads),
            filename);
        request.SetDestinationUri(destinationUri);

        // 启动下载
        var downloadManager = (Android.App.DownloadManager)Android.App.Application.Context.GetSystemService(Android.App.Application.DownloadService);
        downloadManager.Enqueue(request);
    }
}

在MauiProgram.cs中注册这个Handler：

builder.ConfigureMauiHandlers(handlers =>
{
#if ANDROID
    handlers.AddHandler<Microsoft.Maui.Controls.WebView, YourAppName.Platforms.Android.CustomWebViewHandler>();
#endif
});

iOS平台 #

在iOS项目中自定义WebView Handler，通过WKNavigationDelegate处理下载请求：

using WebKit;
using Microsoft.Maui.Handlers;

namespace YourAppName.Platforms.iOS;

public class CustomWebViewHandler : WebViewHandler
{
    protected override void ConnectHandler(WKWebView platformView)
    {
        base.ConnectHandler(platformView);
        platformView.NavigationDelegate = new CustomWKNavigationDelegate();
    }
}

public class CustomWKNavigationDelegate : WKNavigationDelegate
{
    public override void DecidePolicy(WKWebView webView, WKNavigationAction navigationAction, Action<WKNavigationActionPolicy> decisionHandler)
    {
        var request = navigationAction.Request;
        if (request.Url != null && IsDownloadRequest(request))
        {
            webView.Configuration.WebsiteDataStore.HttpCookieStore.GetAllCookies((cookies) =>
            {
                var downloadTask = webView.StartDownload(request);
                downloadTask.Delegate = new CustomWKDownloadDelegate();
            });
            decisionHandler(WKNavigationActionPolicy.Cancel);
            return;
        }

        decisionHandler(WKNavigationActionPolicy.Allow);
    }

    // 简单判断是否为下载请求，可根据实际场景调整
    private bool IsDownloadRequest(NSUrlRequest request)
    {
        var urlString = request.Url.AbsoluteString;
        var downloadExtensions = new[] { ".pdf", ".zip", ".docx", ".xlsx" };
        return downloadExtensions.Any(ext => urlString.EndsWith(ext, StringComparison.OrdinalIgnoreCase));
    }
}

public class CustomWKDownloadDelegate : WKDownloadDelegate
{
    public override void DidFinishDownload(WKDownload download, NSUrl location)
    {
        // 将文件移动到Documents目录，方便用户访问
        var documentsPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
        var destinationPath = Path.Combine(documentsPath, Path.GetFileName(location.AbsoluteString));

        if (File.Exists(destinationPath)) File.Delete(destinationPath);
        File.Move(location.Path, destinationPath);

        // 提示用户下载完成
        var alert = UIKit.UIAlertController.Create("下载完成", $"文件已保存到: {destinationPath}", UIKit.UIAlertControllerStyle.Alert);
        alert.AddAction(UIKit.UIAlertAction.Create("确定", UIKit.UIAlertActionStyle.Default, null));
        UIKit.UIApplication.SharedApplication.KeyWindow?.RootViewController.PresentViewController(alert, true, null);
    }
}

同样在MauiProgram.cs中注册iOS的Handler：

builder.ConfigureMauiHandlers(handlers =>
{
#if IOS
    handlers.AddHandler<Microsoft.Maui.Controls.WebView, YourAppName.Platforms.iOS.CustomWebViewHandler>();
#endif
});

2. 额外配置与注意事项 #

• Android权限：在AndroidManifest.xml中添加必要权限：

  <uses-permission android:name="android.permission.INTERNET" />
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" android:maxSdkVersion="32" />
  <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" android:maxSdkVersion="32" />
  

  Android 13及以上需补充媒体访问权限，可根据需求添加android.permission.READ_MEDIA_IMAGES等。

• iOS文件共享：若要让用户在系统文件应用中看到下载文件，需在Info.plist中添加：

  <key>UIFileSharingEnabled</key>
  <true/>
  <key>LSSupportsOpeningDocumentsInPlace</key>
  <true/>
  

• 动态WebView验证：确保webViewerS创建后能自动关联自定义Handler（全局注册后动态创建的WebView会自动生效），可先用公开下载链接（如https://sample-videos.com/pdf/Sample-pdf-5mb.pdf）测试功能是否正常。

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