带有组合框的 Silverlight DataGrid - 所选项目未显示

Question

我在 Silverlight 数据网格内使用组合框时遇到问题，这两个组合框都绑定到 DataContext，而 DataContext 又使用 RIA 从数据库检索数据。

我遇到的问题是，当您在组合框中选择一个值并单击该单元格时，该单元格显示为空，而不是显示新选择的值的单元格。但是，只有当您选择的值尚未在数据网格的另一个单元格中选择时，才会发生这种情况！选择唯一值会导致该框显示空

我的代码如下：

<navigation:Page x:Class="Chemical_Management_System.EditPermissions" 
       xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
       xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
       xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
       xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
       mc:Ignorable="d"
       xmlns:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"

       d:DesignWidth="640" d:DesignHeight="480"
       Title="EditPermissions Page" Width="640" HorizontalAlignment="Center" 
             xmlns:riaControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.DomainServices" 
             xmlns:my="clr-namespace:Chemical_Management_System.Web" 
             xmlns:myn="clr-namespace:Chemical_Management_System" 
             xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">



<Grid x:Name="LayoutRoot">
    <Border BorderBrush="Silver" BorderThickness="1" Height="45" HorizontalAlignment="Left" Margin="10,10,0,0" Name="Border1" Style="{StaticResource HeaderBackground}" VerticalAlignment="Top" Width="618">
        <TextBlock Height="23" Name="TextBlock21" Style="{StaticResource HeaderText}" Text="Edit Permissions" />
    </Border>
    <riaControls:DomainDataSource AutoLoad="True" d:DesignData="{d:DesignInstance my:Permissions, CreateList=true}" Height="0" Name="PermissionsDomainDataSource" QueryName="GetPermissionsQuery" SubmittedChanges="OnSubmitChanges"  Width="0">
        <riaControls:DomainDataSource.DomainContext>
            <my:DataContext />
        </riaControls:DomainDataSource.DomainContext>
    </riaControls:DomainDataSource>

    <riaControls:DomainDataSource AutoLoad="True" d:DesignData="{d:DesignInstance my:PermissionLookups, CreateList=true}" Height="0" Name="PermissionLookupsDomainDataSource" QueryName="GetPermissionLookupsQuery" Width="0">
        <riaControls:DomainDataSource.DomainContext>
            <my:DataContext />
        </riaControls:DomainDataSource.DomainContext>
    </riaControls:DomainDataSource>

    <riaControls:DomainDataSource AutoLoad="True" d:DesignData="{d:DesignInstance my:Users, CreateList=true}" Height="0" Name="UsersDomainDataSource" QueryName="GetUsersQuery" Width="0">
        <riaControls:DomainDataSource.DomainContext>
            <my:DataContext />
        </riaControls:DomainDataSource.DomainContext>
    </riaControls:DomainDataSource>

    <Button Content="Apply" Height="23" HorizontalAlignment="Left" Margin="553,445,0,0" Name="btnApply" VerticalAlignment="Top" Width="75" />
    <sdk:DataGrid AutoGenerateColumns="False" Height="378" HorizontalAlignment="Left" ItemsSource="{Binding ElementName=PermissionsDomainDataSource, Path=Data}" Margin="12,61,0,0" Name="PermissionsDataGrid" RowDetailsVisibilityMode="VisibleWhenSelected" VerticalAlignment="Top" Width="615">
        <sdk:DataGrid.Columns>

            <sdk:DataGridTemplateColumn Header="User" MinWidth="190">
                <sdk:DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding User.Name}" Padding="5,0,0,0" />
                    </DataTemplate>
                </sdk:DataGridTemplateColumn.CellTemplate>
                <sdk:DataGridTemplateColumn.CellEditingTemplate>
                    <DataTemplate>
                        <ComboBox ItemsSource="{Binding UsersDomainDataSource}" 

                                  Loaded="ComboBoxUsers_Loaded"
                                  SelectionChanged="UsersComboBox_SelectionChanged"
                              >
                            <ComboBox.ItemTemplate>
                                <DataTemplate>
                                    <TextBlock Text="{Binding Name}" />
                                </DataTemplate>
                            </ComboBox.ItemTemplate>

                        </ComboBox>

                    </DataTemplate>
                </sdk:DataGridTemplateColumn.CellEditingTemplate>
            </sdk:DataGridTemplateColumn>
            <sdk:DataGridTemplateColumn Header="Permission" MinWidth="175">
                <sdk:DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding PermissionLookup.Description}" />
                    </DataTemplate>
                </sdk:DataGridTemplateColumn.CellTemplate>
                <sdk:DataGridTemplateColumn.CellEditingTemplate>
                    <DataTemplate>
                        <ComboBox ItemsSource="{Binding PermissionLookupsDomainDataSource}" 

                                  Loaded="ComboBox_Loaded"
                                  SelectionChanged="PermissionLookupComboBox_SelectionChanged"
                              >
                            <ComboBox.ItemTemplate>
                                <DataTemplate>
                                    <TextBlock Text="{Binding Description}" />
                                </DataTemplate>
                            </ComboBox.ItemTemplate>

                        </ComboBox>

                    </DataTemplate>
                </sdk:DataGridTemplateColumn.CellEditingTemplate>
            </sdk:DataGridTemplateColumn>
            <sdk:DataGridTextColumn x:Name="DescriptionColumn" Binding="{Binding Path=Description}" Header="Description" MinWidth="245" />

        </sdk:DataGrid.Columns>
    </sdk:DataGrid>
    <Button Content="New" Height="23" HorizontalAlignment="Left" Margin="12,445,0,0" Name="btnNew" VerticalAlignment="Top" Width="75" />
    <Button Content="Delete" Height="23" HorizontalAlignment="Left" Margin="93,445,0,0" Name="btnDelete" VerticalAlignment="Top" Width="75" />
    <Button Content="Cancel" Height="23" HorizontalAlignment="Left" Margin="472,445,0,0" Name="btnCancel" VerticalAlignment="Top" Width="75" />
</Grid>

Partial Public Class EditPermissions
Inherits Page

Dim Context As New Web.DataContext()
Dim user As New CurrentUser()

Public Sub New()
    InitializeComponent()

    AddHandler user.userLoadedCompleted, AddressOf userLoaded
End Sub

'Executes when the user navigates to this page.
Protected Overrides Sub OnNavigatedTo(ByVal e As System.Windows.Navigation.NavigationEventArgs)

End Sub

Private Sub userLoaded()
    If user.permissionCheck("Admin") = False Then
        MessageBox.Show("You do not have permission to access this page")
        NavigationService.Navigate(New Uri("/Home", UriKind.Relative))
    End If
End Sub

Private Sub PermissionsDomainDataSource_LoadedData(ByVal sender As System.Object, ByVal e As System.Windows.Controls.LoadedDataEventArgs) Handles PermissionsDomainDataSource.LoadedData

    If e.HasError Then
        System.Windows.MessageBox.Show(e.Error.ToString, "Load Error", System.Windows.MessageBoxButton.OK)
        e.MarkErrorAsHandled()
    End If
End Sub


Private Sub PermissionLookupsDomainDataSource_LoadedData(ByVal sender As System.Object, ByVal e As System.Windows.Controls.LoadedDataEventArgs) Handles PermissionLookupsDomainDataSource.LoadedData

    If e.HasError Then
        System.Windows.MessageBox.Show(e.Error.ToString, "Load Error", System.Windows.MessageBoxButton.OK)
        e.MarkErrorAsHandled()
    End If
End Sub

Private Sub ComboBox_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
    ' set combobox items source from wherever you want
    Dim combo As ComboBox = sender
    combo.ItemsSource = Me.PermissionLookupsDomainDataSource.DataView
End Sub

Private Sub ComboBoxUsers_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
    ' set combobox items source from wherever you want
    Dim combo As ComboBox = sender
    combo.ItemsSource = Me.UsersDomainDataSource.DataView
End Sub

Private Sub btnApply_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnApply.Click
    Me.PermissionsDomainDataSource.SubmitChanges()
    NavigationService.Navigate(New Uri("/AdminHome", UriKind.Relative))
End Sub

Private Sub btnDelete_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnDelete.Click
    If PermissionsDataGrid.SelectedItem IsNot Nothing Then
        Dim selected As Web.Permissions = PermissionsDataGrid.SelectedItem
        Me.PermissionsDomainDataSource.DataView.Remove(selected)
    Else
        MessageBox.Show("Please select a permission entry to delete")
    End If

End Sub

Private Sub btnNew_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnNew.Click
    Dim permission As New Web.Permissions
    Me.PermissionsDomainDataSource.DataView.Add(permission)
End Sub

Private Sub btnCancel_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnCancel.Click
    Me.PermissionsDomainDataSource.RejectChanges()
    NavigationService.Navigate(New Uri("/AdminHome", UriKind.Relative))
End Sub

Private Sub OnSubmitChanges(ByVal sender As Object, ByVal e As SubmittedChangesEventArgs)
    If (e.HasError) Then
        MessageBox.Show("Error: " + e.Error.ToString)
    End If

End Sub

Private Sub UsersComboBox_SelectionChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs)

    Dim permission As Web.Permissions = PermissionsDataGrid.SelectedItem
    Dim selected As ComboBox = sender
    Dim user As Web.Users = selected.SelectedItem

    permission.UserID = user.ID
    selected.UpdateLayout()
End Sub

Private Sub PermissionLookupComboBox_SelectionChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs)

    Dim permission As Web.Permissions = PermissionsDataGrid.SelectedItem
    Dim selected As ComboBox = sender
    Dim permissionLookup As Web.PermissionLookups = selected.SelectedItem

    permission.PermissionID = permissionLookup.ID

End Sub
End Class

Answer 1

这是可能的解决方案之一..

http://richardgavel.wordpress.com/2009/04/17/silverlight-combobox-and-asynchronous-population-of-underlying-data/

Answer 2

你知道，我已经解决这个问题很多年了，但找不到解决方案。当我把它发布到网上的那一刻……我突然意识到了。我讨厌这种事发生。不管怎样，解决办法如下。

由于数据库和数据对象是使用强类型链接构建的，因此您可以通过执行 Permission.User.Property 来访问任何给定权限组中引用的用户。您还可以分配给此 Permission.User 来设置链接。

虽然我之前确实尝试使用 DataDomainSources 执行此操作，但它总是给我一个错误，指出该对象已绑定到另一个 DataDomainSources。这是因为您有一个用于权限的 DataDomainSource，还有一个用于用户的 DataDomainSource。

但是，使用 DataContext 时不存在此限制，因为用户和权限都存在于同一 DataContext 中。

因此我重新编写了代码如下：

<navigation:Page x:Class="Chemical_Management_System.EditPermissions" 
       xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
       xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
       xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
       xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
       mc:Ignorable="d"
       xmlns:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"

       d:DesignWidth="640" d:DesignHeight="480"
       Title="EditPermissions Page" Width="640" HorizontalAlignment="Center" 
             xmlns:riaControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.DomainServices" 
             xmlns:my="clr-namespace:Chemical_Management_System.Web" 
             xmlns:myn="clr-namespace:Chemical_Management_System" 
             xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">



<Grid x:Name="LayoutRoot" >
    <Border BorderBrush="Silver" BorderThickness="1" Height="45" HorizontalAlignment="Left" Margin="10,10,0,0" Name="Border1" Style="{StaticResource HeaderBackground}" VerticalAlignment="Top" Width="618">
        <TextBlock Height="23" Name="TextBlock21" Style="{StaticResource HeaderText}" Text="Edit Permissions" />
    </Border>


    <Button Content="Apply" Height="23" HorizontalAlignment="Left" Margin="553,445,0,0" Name="btnApply" VerticalAlignment="Top" Width="75" />
    <Button Content="New" Height="23" HorizontalAlignment="Left" Margin="12,445,0,0" Name="btnNew" VerticalAlignment="Top" Width="75" />
    <Button Content="Delete" Height="23" HorizontalAlignment="Left" Margin="93,445,0,0" Name="btnDelete" VerticalAlignment="Top" Width="75" />
    <Button Content="Cancel" Height="23" HorizontalAlignment="Left" Margin="472,445,0,0" Name="btnCancel" VerticalAlignment="Top" Width="75" />
    <sdk:DataGrid AutoGenerateColumns="False" Height="364" HorizontalAlignment="Left" Margin="10,75,0,0" Name="dataGrid" VerticalAlignment="Top" Width="618" DataContext="dataContext.Permissions">
        <sdk:DataGrid.Columns>
            <sdk:DataGridTextColumn x:Name="DescriptionColumn" Binding="{Binding Path=Description}" Header="Description" MinWidth="245" />

            <sdk:DataGridTemplateColumn Header="User" MinWidth="190">
                <sdk:DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding User.Name}" Padding="5,0,0,0" />
                    </DataTemplate>
                </sdk:DataGridTemplateColumn.CellTemplate>

                <sdk:DataGridTemplateColumn.CellEditingTemplate>
                    <DataTemplate>
                        <ComboBox Loaded="UserComboBox_Loaded" SelectionChanged="UserComboBox_SelectionChanged">
                            <ComboBox.ItemTemplate>
                                <DataTemplate>
                                    <TextBlock Text="{Binding Name}" />
                                </DataTemplate>
                            </ComboBox.ItemTemplate>
                        </ComboBox>
                    </DataTemplate>
                </sdk:DataGridTemplateColumn.CellEditingTemplate>


            </sdk:DataGridTemplateColumn>

            <sdk:DataGridTemplateColumn Header="Permission" MinWidth="190">
                <sdk:DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding PermissionLookup.Description}" Padding="5,0,0,0" />
                    </DataTemplate>
                </sdk:DataGridTemplateColumn.CellTemplate>

                <sdk:DataGridTemplateColumn.CellEditingTemplate>
                    <DataTemplate>
                        <ComboBox Loaded="PermissionComboBox_Loaded" SelectionChanged="PermissionComboBox_SelectionChanged">
                            <ComboBox.ItemTemplate>
                                <DataTemplate>
                                    <TextBlock Text="{Binding Description}" />
                                </DataTemplate>
                            </ComboBox.ItemTemplate>
                        </ComboBox>
                    </DataTemplate>
                </sdk:DataGridTemplateColumn.CellEditingTemplate>


            </sdk:DataGridTemplateColumn>


        </sdk:DataGrid.Columns>
    </sdk:DataGrid>
</Grid>

Partial Public Class EditPermissions
Inherits Page

Dim Context As New Web.DataContext()
Dim user As New CurrentUser()


Public Sub New()
    InitializeComponent()

    AddHandler user.userLoadedCompleted, AddressOf userLoaded

    Context.Load(Context.GetPermissionsQuery())
    Context.Load(Context.GetUsersQuery())
    Context.Load(Context.GetPermissionLookupsQuery)


    dataGrid.ItemsSource = Context.Permissions


End Sub

'Executes when the user navigates to this page.
Protected Overrides Sub OnNavigatedTo(ByVal e As System.Windows.Navigation.NavigationEventArgs)

End Sub

Private Sub userLoaded()
    If user.permissionCheck("Admin") = False Then
        MessageBox.Show("You do not have permission to access this page")
        NavigationService.Navigate(New Uri("/Home", UriKind.Relative))
    End If
End Sub





Private Sub UserComboBox_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs)
    Dim combo As ComboBox = sender
    combo.ItemsSource = Context.Users
End Sub

Private Sub UserComboBox_SelectionChanged(sender As System.Object, e As System.Windows.Controls.SelectionChangedEventArgs)
    Dim combo As ComboBox = sender
    Dim user As Web.Users = combo.SelectedItem

    Dim currentPermission As Web.Permissions = dataGrid.SelectedItem
    currentPermission.User = user

End Sub


Private Sub PermissionComboBox_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs)
    Dim combo As ComboBox = sender
    combo.ItemsSource = Context.PermissionLookups
End Sub

Private Sub PermissionComboBox_SelectionChanged(sender As System.Object, e As System.Windows.Controls.SelectionChangedEventArgs)
    Dim combo As ComboBox = sender
    Dim permissionLookup As Web.PermissionLookups = combo.SelectedItem

    Dim currentPermission As Web.Permissions = dataGrid.SelectedItem
    currentPermission.PermissionLookup = permissionLookup

End Sub

Private Sub btnApply_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles btnApply.Click
    Context.SubmitChanges()
End Sub

Private Sub btnNew_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles btnNew.Click
    Dim newpermission As New Web.Permissions
    Context.Permissions.Add(newpermission)
End Sub


End Class