Question

我正在构建一个WP7应用程序，它包含在第一页中的一个列表框中，以显示多个任务的ID和一个详细信息页面，以显示每个任务（选定）的详细信息。

我需要将任务ID从第一页传递到第二页。我知道它是由列表框的SelectionChanged事件执行的。

这是我的XAML代码：

<phone:PhoneApplicationPage 
    x:Class="TaskListAlpha03.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="696"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait" Orientation="Portrait"
    shell:SystemTray.IsVisible="True"    
    xmlns:controls="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone.Controls">

    <phone:PhoneApplicationPage.Resources>
        <DataTemplate x:Key="TaskListListBoxTemplate">            
            <StackPanel Orientation="Vertical" Margin="0,0,0,20">                
                <TextBlock Text="{Binding Crm_object_id}" FontSize="32" FontFamily="Segoe WP Bold" Foreground="Gray"/>
                <!--<TextBlock Text="{Binding Comment}" Margin="10,0,0,0"/>              -->
            </StackPanel>            
        </DataTemplate>
    </phone:PhoneApplicationPage.Resources>

        <!--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="12,17,0,40">
            <TextBlock x:Name="ApplicationTitle" Text="TASK LIST ALPHA" Style="{StaticResource PhoneTextNormalStyle}"/>
            <TextBlock x:Name="PageTitle" Text="tasks" 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">
            <ListBox 
                        x:Name="allTaskListTasksListBox" 
                        ItemsSource="{Binding AllTaskListTasks}" 
                        ItemTemplate="{StaticResource TaskListListBoxTemplate}"
                        SelectionChanged="allTaskListTasksListBox_SelectionChanged" />
        </Grid>
    </Grid>


</phone:PhoneApplicationPage>

这是cs代码：

    private void allTaskListTasksListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {            
        ListBoxItem lbi = ((sender as ListBox).SelectedItem as ListBoxItem);
        NavigationService.Navigate(new Uri("/View/Details.xaml?msg=" + lbi.Content.ToString(), UriKind.RelativeOrAbsolute));
    }

在第二页中，我有一个示例代码来检查它是否有效：

protected override void OnNavigatedTo
        (System.Windows.Navigation.NavigationEventArgs e)
        {
            base.OnNavigatedTo(e);
            string msg = "";
            if (NavigationContext.QueryString.TryGetValue("msg", out msg))
                PageTitle.Text = msg;
        }

当我执行应用程序时，我有一个“NullReferenceException”。

对不起我的英文：S和谢谢。

Answer 1

问题在于ListBoxItem lbi = ((sender as ListBox).SelectedItem as ListBoxItem);。您将它转换为ListBoxItem，实际上它是您将它绑定到ListBox的自定义项。做类似的事情：

var item = ((sender as ListBox).SelectedItem as YourItem);

Answer 2

这里有几点......
1）我会在项目上使用Tap事件而不是选择更改事件。它有助于防止意外导航 2）如果你做使用selectionchanged事件，请尝试以下代码来获取你的项目。如果在列表中取消选择项目，您的当前代码将尝试触发。

private void allTaskListTasksListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{   
    if(e.AddedItems.Count > 0) // the items that were added to the "selected" collection
    {
        var mySelectedItem = e.AddedItems[0] as myItemType;
        if(null != mySelectedItem) // prevents errors if casting fails
        {
            NavigationService.Navigate(
               new Uri("/View/Details.xaml?msg=" + mySelectedItem.Crm_object_id, 
                       UriKind.RelativeOrAbsolute)
            );
        }
    }
}

ListBox的SelectionChanged事件。在页面之间传递参数

2 个答案: