FragmentTabHost in VS2013 - xamarin C#

我用来创建FragmentTabHost的代码：（我正在为android 2.2以上版本设计）我在谷歌上搜索了很多，但没有用，所以我已经把我所有的代码都放在这里了。我在中出错

   mTabHost.AddTab(spec);

请帮忙怎么解决？？

活动2.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Content.PM;
using Android.Support.V4.App;

namespace ANRestaurant.Forms
{
[Activity(Label = "ANRestaurant", MainLauncher = true, Icon = "@drawable/icon", ScreenOrientation = ScreenOrientation.Portrait)]

public class Activity2 : FragmentActivity
{
    FragmentTabHost mTabHost;
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        SetContentView(Resource.Layout.activity_main);
        try
        {
            mTabHost = FindViewById<FragmentTabHost>(Resource.Id.tabhostN  );
            Intent intent;
            intent = new Intent(this, typeof(Fragment1));
            intent.AddFlags(ActivityFlags.NewTask);
            //mTabHost.Setup(this, SupportFragmentManager, Resource.Id.tabFrameLayout);

            TabHost.TabSpec spec;
            spec = mTabHost.NewTabSpec("artists");
            spec.SetIndicator("Artists", Resources.GetDrawable(Resource.Drawable.tab_icon1)  );
            spec.SetContent(intent);
            mTabHost.AddTab(spec);   ======>Here is the error
            //mTabHost.AddTab(
            //        mTabHost.NewTabSpec("tab2").SetIndicator("Tab 2", null),
            //       intent, null);
            //mTabHost.addTab(
            //        mTabHost.newTabSpec("tab2").setIndicator("Tab 2", null),
            //        FragmentTab.class, null);
            //mTabHost.addTab(
            //        mTabHost.newTabSpec("tab3").setIndicator("Tab 3", null),
            //        FragmentTab.class, null);
        }
        catch (Exception ex)
        {

        }
    }
}
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?> <android.support.v4.app.FragmentTabHost xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/tabhostN" android:layout_width="match_parent" android:layout_height="match_parent"> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <TabWidget android:id="@+id/tabs" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_weight="0" android:orientation="horizontal" /> <FrameLayout android:id="@+id/tabFrameLayout" android:layout_width="match_parent" android:layout_height="0dp" android:layout_weight="1" /> </LinearLayout> </android.support.v4.app.FragmentTabHost>

碎片1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Util;
using Android.Views;
using Android.Widget;

namespace ANRestaurant.Forms
{
public class Fragment1 : Fragment
{

    public override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);

        // Create your fragment here
    }
    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View view = inflater.Inflate(Resource.Layout.fragment1, container, false);
       return view;
         //return base.OnCreateView(inflater, container, savedInstanceState);
    }
}
}

ٍ错误为：Java.Lang.NullPointerException：引发了类型为Java.Lang.NullPointerException的异常。在Android.Runtime.JNIEnv.CallVoidMethod（IntPtr jobject，IntPtr jmethod，Android.Runtime.JValue[]parms）