Excel VSTO插件中如何正确操作ElementHost托管的WPF控件？

我正在开发Excel VSTO插件，想要使用WPF控件，参考相关官方教程后添加了TabControl做测试。需求是点击Ribbon按钮时，根据条件以编程方式切换TabItem并修改其属性，但最初只能访问TabItem的Header文本，无法修改Header或设置IsSelected属性。

最初的错误代码 #

VB代码 #

Imports Microsoft.Office.Tools
Imports Microsoft.Office.Tools.Ribbon

Public Class Ribbon1
    Private myUserControl1 As MyUserControl
    Private myCustomTaskPane As CustomTaskPane

    Private Sub btnCheck_Click(sender As Object, e As RibbonControlEventArgs) Handles btnCheck.Click
        ' Show the taskpane
        myUserControl1 = New MyUserControl
        myCustomTaskPane = Globals.ThisAddIn.CustomTaskPanes.Add(myUserControl1, "Test addin")
        myCustomTaskPane.Width = 500
        myCustomTaskPane.Visible = True
        Dim uc As New UserControl1

        ' Check if there's a table
        If isThereATable() Then
            MsgBox("There is")
            MsgBox(uc.Tab2.Header) ' works
            uc.Tab2.Header = "new header" ' does not work

        Else
            MsgBox("There is not")
        End If

    End Sub
End Class

对应的WPF XAML代码 #

<UserControl x:Class="UserControl1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:AutoTable"
             mc:Ignorable="d" 
             d:DesignHeight="450" Width="500">
    <Grid Width="500">
        <TabControl BorderThickness="1" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" HorizontalAlignment="Left" Width="500" Name="MainTab">
            <TabItem Header="Init" Name="Tab1" >
                <Grid Background="#FFE5E5E5" Margin="0">
                    <TextBlock HorizontalAlignment="Left" TextWrapping="Wrap" Text="The following button should create a table." VerticalAlignment="Top" FontSize="16" Margin="10,10,0,0"/>
                    <Button Content="Create table" HorizontalAlignment="Left" Margin="5,60,0,0" VerticalAlignment="Top" Width="100" Click="Button_Click" Height="30" FontSize="14"/>
                </Grid>
            </TabItem>
            <TabItem Header="CC" Name="Tab2" >
                <Grid Background="#FFE5E5E5"/>
            </TabItem>
        </TabControl>
    </Grid>
</UserControl>

问题原因与解决方法 #

核心问题 #

1. 控件托管要求：Excel VSTO的CustomTaskPane仅支持托管Windows Forms控件，WPF用户控件必须嵌套在Windows Forms用户控件中才能被正确加载。
2. 实例引用错误：最初代码中初始化了新的UserControl1实例uc，但修改的是这个未加载到界面的实例属性，而非已经添加到任务窗格的那个实例，导致界面无变化。

修正后的代码 #

Public Class Ribbon1
    Private ThisUserControl As UserControlWF
    Private ThisTaskPane As Microsoft.Office.Tools.CustomTaskPane

    Private Sub ShowTaskPane_Click(sender As Object, e As RibbonControlEventArgs) Handles ShowTaskPane.Click
        ThisUserControl = New UserControlWF

        ' CustomTaskPanes只能添加Windows Forms UI元素，直接添加WPF控件会报错
        ThisTaskPane = Globals.ThisAddIn.CustomTaskPanes.Add(ThisUserControl, "Title")
        ThisTaskPane.Width = 510
        ThisTaskPane.Visible = True

        ' 加载任务窗格后根据条件修改控件属性
        If isThereATable() Then
            MsgBox("There is a table")
            ' 修改已加载到界面的WPF控件实例属性
            ThisUserControl.UserControlWPF1.Tab2.Header = "Different Header" ' 原Header为"TabItem2"
            ThisUserControl.UserControlWPF1.Tab2.IsSelected = True ' 默认选中Tab1

            ' 错误做法：初始化新实例而非操作已加载的实例
            ' Dim uc As New UserControlWPF
            ' MsgBox(uc.Tab2.Header) ' 能读取类默认属性
            ' uc.Tab2.Header = "Different Header" ' 修改的是未加载的实例，界面无变化
        Else
            MsgBox("There is no table")
        End If
    End Sub
End Class

内容的提问来源于stack exchange，提问作者Edgar O.