capture webview andriod.xamarin

using System;
using Android.App;
using Android.OS;
using Android.Widget;
using System.IO;
using Android.Webkit;
using Android.Graphics;
using Android.Graphics.Drawables;
using Android.Util;
using Java.IO;
using System.Diagnostics;

namespace test
{
[Activity (Label = "test", MainLauncher = true)]
public class Activity1 : Activity
{


protected override void OnCreate (Bundle bundle)
{
base.OnCreate (bundle);

// Set our view from the "main" layout resource
SetContentView (Resource.Layout.Main);

// Get our button from the layout resource,
// and attach an event to it
            Button button = FindViewById<Button>(Resource.Id.myButton);
            WebView webview = FindViewById<WebView>(Resource.Id.webView1);
            string id = "103230006";
            webview.LoadUrl("www.google.com");
            button.Click += delegate
            {
           
                Picture picture = webview.CapturePicture();    
                Bitmap bmp = Bitmap.CreateBitmap(picture.Width , picture.Height
                                                    , Bitmap.Config.Argb8888);
                Canvas canvas = new Canvas(bmp);
             
                picture.Draw(canvas);
                FileStream fs = new FileStream("/storage/sdcard0/file.jpg", FileMode.Create, FileAccess.Write);
                bmp.Compress(Bitmap.CompressFormat.Jpeg, 80, fs);
             
                    fs.Close();
            };
}
}
}

==========================LAYOUT================================
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:p1="http://schemas.android.com/apk/res/android"
    p1:orientation="vertical"
    p1:minWidth="25px"
    p1:minHeight="25px"
    p1:layout_width="fill_parent"
    p1:layout_height="fill_parent"
    p1:id="@+id/linearLayout1">
    <WebView
        p1:layout_width="fill_parent"
        p1:layout_height="wrap_content"
        p1:id="@+id/webView1"
        p1:layout_marginBottom="30dp" />
    <Button
        p1:text="Button"
        p1:layout_width="fill_parent"
        p1:layout_height="wrap_content"
        p1:id="@+id/myButton" />
</LinearLayout>