在 Xamarin Android 上实现下载侦听器接口

Question

直到今天，我从未想过要从 Urls 下载文件，需要在他的 Activity 类上实现接口下载监听器。我在 Xamarin Android 中有一个 webview，但我似乎无法下载文件.. 想那是因为我还没有在我的班级上实现这个接口下载监听器..所以我试了一下，但我似乎无法将接口实现方法与OnDwnloadStart 方法连接起来，我想当我请求从网络下载时页面然后 IDownloadListener 方法什么都不做，因为它没有代码....但是应该处理下载请求的代码在带有 url, ContentDisposition and mimetype 参数的 OnDownloadStart 方法中，任何进行接口调用 OnDownloadStart 方法的 hep 肯定会不胜感激..这是我使用的代码...

class Internet : AppCompatActivity,IDownloadListener
    {
       protected override void OnCreate(Bundle savedInstanceState)
        {

            base.OnCreate(savedInstanceState);
            Xamarin.Essentials.Platform.Init(this, savedInstanceState);
            SetContentView(Resource.Layout.Browser);
           //Webview definition
         webview = this.FindViewById<WebView>(Resource.Id.webview1);
           //webview properties
            webview.SetWebViewClient(new WebViewClient());
            WebSettings webSettings = webview.Settings;
            webSettings.SetSupportMultipleWindows(true);
            webSettings.SetEnableSmoothTransition(true);
            webSettings.JavaScriptEnabled = true;
            webSettings.DomStorageEnabled = true;
            webSettings.AllowFileAccessFromFileURLs = true;
            // webSettings.JavaScriptEnabled.
            webview.SetDownloadListener(this);
      }
     //Interface Download Listener Method
       public interface IDownloadListener : Android.Runtime.IJavaObject, IDisposable
        {
         //I got nothing here and this is what i think needs to call OndownloadStart  
        }
      //implementing OnDownloadStart Method
       public void OnDownloadStart(string url, string userAgent, string contentDisposition, string mimetype, long contentLength)
        {
            DownloadManager.Request request = new DownloadManager.Request(Android.Net.Uri.Parse(url));
            String cookies = CookieManager.Instance.GetCookie(url);
            request.AddRequestHeader("cookie", cookies);
            request.AddRequestHeader("User-Agent", userAgent);
            request.SetDescription("Downloading file to crn folder...");
            request.SetTitle(URLUtil.GuessFileName(url, contentDisposition, mimetype));
            request.AllowScanningByMediaScanner();
            request.SetNotificationVisibility(Android.App.DownloadVisibility.VisibleNotifyCompleted);
            File dest = new File(Android.OS.Environment.RootDirectory + "download");
            if (!dest.Exists())
            {
                if (!dest.Mkdir())
                { Log.Debug("TravellerLog ::", "Problem creating Image folder"); }
            }
            request.SetDestinationInExternalFilesDir(Application.Context, "download", 
       URLUtil.GuessFileName(url, contentDisposition, mimetype));
            DownloadManager manager = 
       (DownloadManager)GetSystemService(Android.App.Application.DownloadService);
            manager.Enqueue(request);
            //Notify if success with BroadCast Receiver
        }
}

这段代码的哪一部分运行错误？任何帮助表示赞赏..

Answer 1

不需要新建IDownloadListener接口，IDownloadListener接口是IDownloadListener下namespace Android.Webkit下的系统：

namespace Android.Webkit
{
    [Register("android/webkit/DownloadListener", "", "Android.Webkit.IDownloadListenerInvoker", ApiSince = 1)]
    public interface IDownloadListener : IJavaObject, IDisposable, IJavaPeerable
    {
        void OnDownloadStart(string url, string userAgent, string contentDisposition, string mimetype, long contentLength);
    }
}

实现 IDownloadListener 接口的任何类或结构都必须包含与接口指定的 OnDownloadStart 匹配的 Equals 方法的定义。

所以就像这样：

public class MainActivity : AppCompatActivity, IDownloadListener
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
       SetContentView(Resource.Layout.activity_main);

    }

    public void OnDownloadStart(string url, string userAgent, string contentDisposition, string mimetype, long contentLength)
    {
        throw new NotImplementedException();
    }
}