Xamarin表单MainActivity OnCreate LoadApplication System.NullReferenceException：对象引用未设置为对象的实例

我将VS2015与Xamarin一起使用来创建一个多平台项目，该项目可以显示初始屏幕，然后在webview中加载网页。这是我的项目结构。我正在使用以下PCL项目类型：

TheApp（便携式）

-WebPageHoster.Xaml     //Contains a WebView control
   -WebPageHoster.Xaml.cs  //sets the WebView controls source property to load a webpage
   -App.Xaml
   -App.Xaml.cs

App.Droid

/Resources/drawable/splashlogo.png
/Resources/drawable/icon3.png
/Resources/values/Styles.xml
-MainActivity.cs
-SplashActivity.cs     

TheApp.iOS

TheApp.WindowsPhone（Windows Phone 8.1）

这是 Styles.xml

<?xml version="1.0" encoding="utf-8" ?> 
<resources>
    <style name="Theme.Splash" parent="android:Theme">
        <item name="android:windowBackground">@drawable/splashlogo</item>
        <item name="android:windowNoTitle">true</item>
    </style>
</resources>

SplashActivity.cs

[Activity(MainLauncher = true, NoHistory = true, Theme = "@style/Theme.Splash", Icon = "@drawable/icon3")]
public class SplashActivity : AppCompatActivity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        var intent = new Intent(this, typeof(MainActivity));
        StartActivity(intent);
        Finish();
    }
}

MainActivity.cs

[Activity(Label = "Splash App",  ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsApplicationActivity
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
        global::Xamarin.Forms.Forms.Init(this, bundle);
        LoadApplication(new App());  // << Problem here
    }

所述LoadApplication方法调用OnCreate方法上述负载的App.Xaml.cs类的应用程序的构造，其运行如下代码

公共App（）{InitializeComponent（）; MainPage = new NavigationPage（new WebPageHoster（）{标题=“加载网页”}）; }

这将显示初始屏幕，并在设置WebView的url后返回到OnCreate方法并给出此错误

System.NullReferenceException: Object reference not set to an instance of an object

我无法找到导致此错误的原因。这是Android清单文件。

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="TheApp.TheApp" android:installLocation="auto" android:versionCode="1">
    <uses-sdk android:minSdkVersion="15" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
    <application android:icon="@drawable/icon3" android:theme="@style/Theme.AppCompat" android:label="Splash Web Host"></application>
</manifest>