Question

我正在使用带有DataTemplate的ListBox。

                <ListBox Grid.Row="1" Grid.ColumnSpan="3" Grid.RowSpan="3" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" 
                                ItemsSource="{Binding Order.OrderLines}" >
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <Grid>
                            <Grid.RowDefinitions>
                                <RowDefinition />
                                <RowDefinition />
                                <RowDefinition />
                            </Grid.RowDefinitions>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition />
                                <ColumnDefinition />
                            </Grid.ColumnDefinitions>

                            <TextBlock Grid.Column="0">Qty</TextBlock>
                            <TextBox Text="{Binding LineQty, Mode=TwoWay}" Grid.Column="1" />

                            <TextBlock Grid.Row="1" Grid.Column="0">Weight</TextBlock>
                            <TextBox Text="{Binding Path=LineWeight}" Grid.Row="1" Grid.Column="1" />

                            <TextBlock Grid.Column="0" Grid.Row="2">Pallet Weights</TextBlock>
                            <TextBox Text="{Binding PalletWeights}" Grid.Row="2" Grid.Column="1" />
                        </Grid>
                    </DataTemplate>
                </ListBox.ItemTemplate>

            </ListBox>

TextBox值正确绑定。问题是我的ViewModel上有一个名为“ViewMode”的属性，我将TextBox的IsEnabled属性绑定到App.xaml Style DataTrigger：

            <Style TargetType="{x:Type TextBox}">
            <Style.Triggers>
                <DataTrigger Binding="{Binding ViewMode}" Value="Add">
                    <Setter Property="BorderBrush" Value="White"></Setter>
                    <Setter Property="BorderThickness" Value="2,2,0,0"></Setter>
                    <Setter Property="BorderBrush" Value="Black"></Setter>
                    <Setter Property="BorderThickness" Value="0,0,2,2"></Setter>
                    <Setter Property="Background" Value="LightBlue"></Setter>
                    <Setter Property="Foreground" Value="Black"></Setter>
                    <Setter Property="FontWeight" Value="Bold"></Setter>
                    <Setter Property="IsEnabled" Value="true"></Setter>
                </DataTrigger>
                <DataTrigger Binding="{Binding ViewMode}" Value="Edit">
                    <Setter Property="BorderBrush" Value="White"></Setter>
                    <Setter Property="BorderThickness" Value="2,2,0,0"></Setter>
                    <Setter Property="BorderBrush" Value="Black"></Setter>
                    <Setter Property="BorderThickness" Value="0,0,2,2"></Setter>
                    <Setter Property="Background" Value="LightBlue"></Setter>
                    <Setter Property="Foreground" Value="Black"></Setter>
                    <Setter Property="FontWeight" Value="Bold"></Setter>
                    <Setter Property="IsEnabled" Value="true"></Setter>
                </DataTrigger>
                <DataTrigger Binding="{Binding ViewMode}" Value="View">
                    <Setter Property="IsEnabled" Value="false"></Setter>
                    <Setter Property="Foreground" Value="Gray"></Setter>
                </DataTrigger>
            </Style.Triggers>
            <Setter Property="Margin" Value="2" />
        </Style>

这适用于我的所有其他TextBox。如何从DataTemplate中获取IsEnabled属性？ ListBox的DataContext引用了ViewModel属性“Order”，所以我认为它应该能够看到ViewModel属性“ViewMode”。

谢谢， -sid。

Answer 1

在DataTemplate中，您无法直接从ViewModel访问属性（您不会'继承'DataContext）。假设您的ViewModel是整个视图的DataContext，您可以创建一个代理：

class BindingProxy : Freezable
{

    #region Freezable Members

    protected override Freezable CreateInstanceCore()
    {
        return new BindingProxy();
    }

    #endregion

    /// <summary>
    /// Saves the DataContext from the whole view
    /// </summary>
    public object DataContext
    {
        get { return (object)GetValue(DataContextProperty); }
        set { SetValue(DataContextProperty, value); }
    }

    public static readonly DependencyProperty DataContextProperty =
        DependencyProperty.Register("DataContext", typeof(object), typeof(BindingProxy), new UIPropertyMetadata(null));
}

然后，在您的XAML文件中，您需要引用BindingProxy所在的命名空间：

<UserControl xmlns:utilities="clr-namespace:MyApp.NamespaceWhereBindingProxyIsLocated"
...

稍后，您为视图创建一个BindingProxy实例，并将其与视图的DataContext链接（请注意DataContext = {Binding}部分）：

<UserControl.Resources>
   <utilities:BindingProxy x:Key="proxy" DataContext="{Binding}"/>
</UserControl.Resources>

最后，您可以将它用作每个TextBox的DataContext：

<ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        ..
                        <TextBox Text="{Binding Path={TemplateBinding DataContext.LineQty}, Mode=TwoWay}" DataContext="{Binding Source={StaticResource proxy}, Path=DataContext}"/>
                        ..
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>

希望有所帮助

Answer 2

您需要在Binding中使用RelativeSource标记扩展名，以防您想要像这样前往Visual Tree -

<DataTrigger Binding="{Binding DataContext.ViewMode,
             RelativeSource={RelativeSource FindAncestor,
                               AncestorType = UserControl}}" 
             Value="Add">
</DataTrigger>

默认DataContext TextBox将object of OrderLine LineQty您的财产ViewMode所在的位置。因此，样式在OrderLine的对象而不是ViewModel中搜索DataContext属性，因此您需要使用RelativeSource明确要求它在您的UserControl的ViewModel中搜索它。你的{{1}}。

DataTemplate将ListBox绑定到ViewModel属性

2 个答案: