问未声明的前缀。如何在Windows Phone中声明？

EN

Error   1   'mvvmnavigation' is an undeclared prefix. Line 1, position 2.


<mvvmnavigation:baseapplicationpage 
    x:Class="MVVMNavigation.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"
    mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait" Orientation="Portrait"
    shell:SystemTray.IsVisible="True">

    <!--LayoutRoot is the root grid where all 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="12,17,0,28">
            <TextBlock x:Name="ApplicationTitle" Text="MY APPLICATION" Style="{StaticResource PhoneTextNormalStyle}"/>
            <TextBlock x:Name="PageTitle" Text="page name" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/>
        </StackPanel>

        <!--ContentPanel - place additional content here-->
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0"></Grid>
    </Grid>

    <!--Sample code showing usage of ApplicationBar-->
    <!--<phone:PhoneApplicationPage.ApplicationBar>
        <shell:ApplicationBar IsVisible="True" IsMenuEnabled="True">
            <shell:ApplicationBarIconButton IconUri="/Images/appbar_button1.png" Text="Button 1"/>
            <shell:ApplicationBarIconButton IconUri="/Images/appbar_button2.png" Text="Button 2"/>
            <shell:ApplicationBar.MenuItems>
                <shell:ApplicationBarMenuItem Text="MenuItem 1"/>
                <shell:ApplicationBarMenuItem Text="MenuItem 2"/>
            </shell:ApplicationBar.MenuItems>
        </shell:ApplicationBar>
    </phone:PhoneApplicationPage.ApplicationBar>-->

</mvvmnavigation:baseapplicationpage>

namespace MVVMNavigation
{
    public partial class MainPage : MVVMNavigation.BaseApplicationPage
    {
        // Constructor
        public MainPage()
        {
            InitializeComponent();
        }
    }
}

using System;
using GalaSoft.MvvmLight.Messaging;
using Microsoft.Phone.Controls;

namespace MVVMNavigation
{
    public class BaseApplicationPage : PhoneApplicationPage
    {
        public void NavigateTo(Uri uri)
        {
            if (uri.ToString() == "/GoBack.xaml")
                NavigationService.GoBack();
            else
                NavigationService.Navigate(uri);
        }

        protected override void OnNavigatedFrom(System.Windows.Navigation.NavigationEventArgs e)
        {
            Messenger.Default.Unregister<Uri>(this);
            base.OnNavigatedFrom(e);
        }

        protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
        {
            Messenger.Default.Register<Uri>(this, "NavigationRequest", NavigateTo);
            base.OnNavigatedTo(e);
        }
    }
}