windows-phone-7 - this.DataContext 是 NULL 吗？用于填充 - 切换到 Autofac

Question

我正在使用 MVVM Light、适用于 windows phone 7 的 Autofac 和 Autofac 定位器。

使用自动法

http://www.nuget.org/packages/Autofac.Wp7

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Ioc;
using Microsoft.Practices.ServiceLocation;
using MvvmLight1.Model;
using Autofac;

namespace MvvmLight1.ViewModel
{
    public class ViewModelLocator
    {
        static ViewModelLocator()
        {
            var builder = new ContainerBuilder();

            builder.RegisterType<MainViewModel>();

            var container = builder.Build();
            ServiceLocator.SetLocatorProvider(() => new AutofacServiceLocator(container));
        }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance",
            "CA1822:MarkMembersAsStatic",
            Justification = "This non-static member is needed for data binding purposes.")]
        public MainViewModel Main
        {
            get
            {
                return ServiceLocator.Current.GetInstance<MainViewModel>();
            }
        }
    }
} 


using Microsoft.Phone.Controls;

namespace MvvmLight1
{
    public partial class MainPage : PhoneApplicationPage
    {
        // Constructor
        public MainPage()
        {
            InitializeComponent();
            var main = this.DataContext as MainPage; // will be null
        }
    }
}

<phone:PhoneApplicationPage x:Class="MvvmLight1.MainPage"
                            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                            xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
                            xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
                            xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
                            xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
                            xmlns:ignore="http://www.ignore.com"
                            mc:Ignorable="d ignore"
                            FontFamily="{StaticResource PhoneFontFamilyNormal}"
                            FontSize="{StaticResource PhoneFontSizeNormal}"
                            Foreground="{StaticResource PhoneForegroundBrush}"
                            SupportedOrientations="Portrait"
                            Orientation="Portrait"
                            d:DesignWidth="480"
                            d:DesignHeight="768"
                            shell:SystemTray.IsVisible="True"
                            DataContext="{Binding Main, Source={StaticResource Locator}}">

    <!--LayoutRoot contains the root grid where all other page content is placed-->
    <Grid x:Name="LayoutRoot"
          Background="Transparent">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <!--TitlePanel contains the name of the application and page title-->
        <StackPanel x:Name="TitlePanel"
                    Grid.Row="0"
                    Margin="24,24,0,12">
            <TextBlock x:Name="ApplicationTitle"
                       Text="{Binding ApplicationTitle}"
                       Style="{StaticResource PhoneTextNormalStyle}" />
            <TextBlock x:Name="PageTitle"
                       Text="{Binding PageName}"
                       Margin="-3,-8,0,0"
                       Style="{StaticResource PhoneTextTitle1Style}" />
        </StackPanel>

        <!--ContentPanel - place additional content here-->
        <Grid x:Name="ContentGrid"
              Grid.Row="1">

            <TextBlock Text="{Binding WelcomeTitle}"
                       Style="{StaticResource PhoneTextNormalStyle}"
                       HorizontalAlignment="Center"
                       VerticalAlignment="Center"
                       FontSize="40" 
                       TextWrapping="Wrap" 
                       TextAlignment="Center" />

        </Grid>
    </Grid>
</phone:PhoneApplicationPage>


using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using Autofac;
using Microsoft.Practices.ServiceLocation;

namespace MvvmLight1
{
    public sealed class AutofacServiceLocator : ServiceLocatorImplBase
    {
        readonly IComponentContext _container;

        public AutofacServiceLocator(IComponentContext container)
        {
            if (container == null)
                throw new ArgumentNullException("container");
            _container = container;
        }

        protected override object DoGetInstance(Type serviceType, string key)
        {
            return key != null ? _container.ResolveNamed(key, serviceType) : _container.Resolve(serviceType);
        }

        protected override IEnumerable<object> DoGetAllInstances(Type serviceType)
        {
            var enumerableType = typeof(IEnumerable<>).MakeGenericType(serviceType);

            object instance = _container.Resolve(enumerableType);
            return ((IEnumerable)instance).Cast<object>();
        }
    }
}


using GalaSoft.MvvmLight;
using MvvmLight1.Model;

namespace MvvmLight1.ViewModel
{
    public class MainViewModel : ViewModelBase
    {
        public MainViewModel()
        {

        }
    }
}

现在我的 MainPage.cs 构造函数中的 viewModel 将始终为空。

当我刚刚使用 SimpleIoc 时，它被主对象填充。