大家帮小弟调一下子这个error

大家帮小弟调一下这个error


错误：

错误 1 Event handler 'LongListSelector_SelectionChanged' not found on class 'welcome.MainPage'

<phone:PhoneApplicationPage

    x:Class="welcome.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:DataContext="{d:DesignData SampleData/MainViewModelSampleData.xaml}"

    FontFamily="{StaticResource PhoneFontFamilyNormal}"

    FontSize="{StaticResource PhoneFontSizeNormal}"

    Foreground="{StaticResource PhoneForegroundBrush}"

    SupportedOrientations="Portrait"  Orientation="Portrait"

    shell:SystemTray.IsVisible="False">


    <Grid x:Name="LayoutRoot" Background="Transparent">


        <phone:Panorama Title="Time Machine" FontFamily="Segoe WP Black">

            <phone:Panorama.Background>

                <ImageBrush ImageSource="/welcome;component/Assets/BGP.png"/>

            </phone:Panorama.Background>


            <phone:PanoramaItem Header="     LOOK!" FontWeight="Bold" FontStyle="Italic" FontFamily="Andy" FontSize="24">

                

                            <StackPanel Margin="0,-6,0,12">

                                <TextBlock Text="Time is ELAPSEING......" FontSize="48"/>

                            </StackPanel>

                       

            </phone:PanoramaItem>


            <phone:PanoramaItem>

                <phone:LongListSelector Margin="0,-38,-22,2" ItemsSource="{Binding Items}" SelectionChanged="LongListSelector_SelectionChanged">

                    <phone:LongListSelector.ListHeaderTemplate>

                        <DataTemplate>

                            <Grid Margin="12,0,0,38">

                                <Grid.RowDefinitions>

                                    <RowDefinition Height="Auto"/>

                                    <RowDefinition Height="*"/>

                                </Grid.RowDefinitions>

                                <TextBlock Text="    HEARD!"

                                           Style="{StaticResource PanoramaItemHeaderTextStyle}"

                                           Grid.Row="0" FontWeight="Bold" FontStyle="Italic"/>