将DataTemplate与ContentControl绑定到ContentTemplateSelector

Question

我的Window.Resources中有3个Window.Resources，强类型为三个不同的类：

<DataTemplate x:Key="myTemplateA" DataType="{x:Type local:SampleClassA}">
    <Grid>
        <TextBlock Text="{Binding Path=SampleProperty1}"></TextBlock>
        <TextBlock Text="{Binding Path=SampleProperty2}"></TextBlock>
        <TextBlock Text="{Binding Path=SamplePropertyA}"></TextBlock>
    </Grid>
</DataTemplate>

<DataTemplate x:Key="myTemplateB" DataType="{x:Type local:SampleClassB}">
    <Grid>
        <TextBlock Text="{Binding Path=SampleProperty1}"></TextBlock>
            <TextBlock Text="{Binding Path=SampleProperty2}"></TextBlock>
            <TextBlock Text="{Binding Path=SamplePropertyB}"></TextBlock>
        </Grid>
    </DataTemplate>

    <DataTemplate x:Key="myTemplateBase" DataType="{x:Type local:SampleClass}">
        <Grid>
            <TextBlock Text="{Binding Path=SampleProperty1}"></TextBlock>
            <TextBlock Text="{Binding Path=SampleProperty2}"></TextBlock>
        </Grid>
    </DataTemplate>

还有一个小小的DataTemplateSelector：

<local:SampleDataTemplateSelector x:Key="myBindPropertyTemplateSelector"
    TemplateA="{StaticResource myTemplateA}"
    TemplateB="{StaticResource myTemplateB}" 
    SampleClassBaseTemplate="{StaticResource myTemplateBase}" />

显然，有一个DataTemplateSelector类，称为SampleDataTemplateSelector。

Public Class SampleDataTemplateSelector
    Inherits DataTemplateSelector

    Public Property TemplateA As DataTemplate
    Public Property TemplateB As DataTemplate
    Public Property SampleClassBaseTemplate As DataTemplate

    Public Overrides Function SelectTemplate(item As Object, container As DependencyObject) As DataTemplate

        If item Is Nothing Then Return SampleClassBaseTemplate

        If item.GetType.Equals(GetType(SampleClassA)) Then
            Return TemplateA
        End If

        If item.GetType.Equals(GetType(SampleClassB)) Then
            Return TemplateB
        End If

        Return SampleClassBaseTemplate
    End Function

End Class

DataTemplateSelector必须区分3个简单的类: SampleClass和2个派生类SampleClassA、SampleClassB。

Public Class SampleClass
    Public Property SampleProperty1 As String = "Class SampleClass Property1"
    Public Property SampleProperty2 As String = "Class SampleClass Property2"
End Class

Public Class SampleClassA
    Inherits SampleClass
    Public Property SamplePropertyA As String = "Class SampleClassA"
End Class

Public Class SampleClassB
    Inherits SampleClass
    Public Property SamplePropertyB As String = "Class SampleClassB"
End Class

在我的窗口xaml中，ContentControl设置如下：

<ContentControl Content="{Binding BindProperty}" ContentTemplateSelector="{StaticResource myBindPropertyTemplateSelector}" />

其中BindProperty是在后面的窗口代码上定义的属性：

Dim myBindProperty As SampleClass
Public ReadOnly Property BindProperty As SampleClass
    Get
        Return myBindProperty
    End Get
End Property

毕竟，在我的窗口加载事件中存在BindProperty初始化。

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
    myBindProperty = New SampleClassA()
End Sub

没有编译错误。在执行过程中，SampleDataTemplateSelector的SelectTemplate例程上的item参数从来都不是什么，所以它不能选择正确的模板.什么都没显示出来。我做错什么了？

Answer 1

我重新创建了您的项目，如果您将DataContext = Me添加到Window_Loaded中，它就会工作。我将您的模板更改为使用StackPanel而不是网格(这样文本块就不会相互重叠)。以下是一个完整的工作版本：

​

​

MainWindow.xaml

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication20"
    Loaded="Window_Loaded"
    Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <DataTemplate x:Key="myTemplateA" DataType="{x:Type local:SampleClassA}">
            <StackPanel>
                <TextBlock Text="{Binding Path=SampleProperty1}"></TextBlock>
                <TextBlock Text="{Binding Path=SampleProperty2}"></TextBlock>
                <TextBlock Text="{Binding Path=SamplePropertyA}"></TextBlock>
            </StackPanel>
        </DataTemplate>

        <DataTemplate x:Key="myTemplateB" DataType="{x:Type local:SampleClassB}">
            <StackPanel>
                <TextBlock Text="{Binding Path=SampleProperty1}"></TextBlock>
                <TextBlock Text="{Binding Path=SampleProperty2}"></TextBlock>
                <TextBlock Text="{Binding Path=SamplePropertyB}"></TextBlock>
            </StackPanel>
        </DataTemplate>

        <DataTemplate x:Key="myTemplateBase" DataType="{x:Type local:SampleClass}">
            <StackPanel>
                <TextBlock Text="{Binding Path=SampleProperty1}"></TextBlock>
                <TextBlock Text="{Binding Path=SampleProperty2}"></TextBlock>
            </StackPanel>
        </DataTemplate>

        <local:SampleDataTemplateSelector x:Key="myBindPropertyTemplateSelector"
            TemplateA="{StaticResource myTemplateA}"
            TemplateB="{StaticResource myTemplateB}" 
            SampleClassBaseTemplate="{StaticResource myTemplateBase}" />
    </Window.Resources>
    <Grid>
        <ContentControl Content="{Binding BindProperty}" ContentTemplateSelector="{StaticResource myBindPropertyTemplateSelector}" />
    </Grid>
</Window>

MainWindow.xaml.vb

Class MainWindow 
    Dim myBindProperty As SampleClass
    Public ReadOnly Property BindProperty As SampleClass
        Get
            Return myBindProperty
        End Get
    End Property

    Private Sub Window_Loaded(sender As Object, e As RoutedEventArgs)
        myBindProperty = New SampleClassA()
        DataContext = Me
    End Sub
End Class

Public Class SampleClass
    Public Property SampleProperty1 As String = "Class SampleClass Property1"
    Public Property SampleProperty2 As String = "Class SampleClass Property2"
End Class

Public Class SampleClassA
    Inherits SampleClass
    Public Property SamplePropertyA As String = "Class SampleClassA"
End Class

Public Class SampleClassB
    Inherits SampleClass
    Public Property SamplePropertyB As String = "Class SampleClassB"
End Class

Public Class SampleDataTemplateSelector
    Inherits DataTemplateSelector

    Public Property TemplateA As DataTemplate
    Public Property TemplateB As DataTemplate
    Public Property SampleClassBaseTemplate As DataTemplate

    Public Overrides Function SelectTemplate(item As Object, container As DependencyObject) As DataTemplate

        If item Is Nothing Then Return SampleClassBaseTemplate

        If item.GetType.Equals(GetType(SampleClassA)) Then
            Return TemplateA
        End If

        If item.GetType.Equals(GetType(SampleClassB)) Then
            Return TemplateB
        End If

        Return SampleClassBaseTemplate
    End Function

End Class