MyToolWindowControl.xaml

<DataTemplate xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:vs="http://schemas.microsoft.com/visualstudio/extensibility/2022/xaml"
              xmlns:styles="clr-namespace:Microsoft.VisualStudio.Shell;assembly=Microsoft.VisualStudio.Shell.15.0"
              xmlns:colors="clr-namespace:Microsoft.VisualStudio.PlatformUI;assembly=Microsoft.VisualStudio.Shell.15.0">
  <Border Background="{DynamicResource {x:Static colors:EnvironmentColors.ToolWindowBackgroundBrushKey}}"
          TextElement.Foreground="{DynamicResource {x:Static colors:EnvironmentColors.ToolWindowTextBrushKey}}"
          Padding="5">
    <StackPanel Orientation="Horizontal"
                HorizontalAlignment="Center"
                VerticalAlignment="Center">
      <TextBlock Margin="0,0,5,0"
                 Text="Custom Message:"
                 VerticalAlignment="Center" />
            <TextBox x:Name="TitleTextBox"
                     MinHeight="26"
                     MinWidth="200"
                     HorizontalContentAlignment="Left"
                     VerticalContentAlignment="Center"
                     Text="{Binding Message, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                     Style="{StaticResource {x:Static styles:VsResourceKeys.TextBoxStyleKey}}">
                <TextBox.ContextMenu>
                  <ContextMenu Style="{DynamicResource {x:Static styles:VsResourceKeys.ContextMenuStyleKey}}">
                    <MenuItem Header="Clear" Command="{Binding ClearCommand}">
                      <MenuItem.Icon>
                        <vs:Image Source="KnownMonikers.ClearWindowContent" />
                      </MenuItem.Icon>
                    </MenuItem>
                    <MenuItem Header="Default message" Command="{Binding DefaultTextCommand}">
                      <MenuItem.Icon>
                        <vs:Image Source="DefaultText" />
                      </MenuItem.Icon>
                    </MenuItem>
                  </ContextMenu>
                </TextBox.ContextMenu>
            </TextBox>
            <Button x:Name="ShowMessageButton"
                    Content="Show Dialog"
                    IsEnabled="False"
                    Margin="5,0,0,0"
                    MinHeight="25"
                    MinWidth="60"
                    Style="{StaticResource {x:Static styles:VsResourceKeys.ButtonStyleKey}}"
                    Command="{Binding ShowMessageCommand}" />
    </StackPanel>
  </Border>
  <DataTemplate.Triggers>
    <DataTrigger Binding="{Binding HasError}" Value="False">
      <Setter TargetName="ShowMessageButton" Property="IsEnabled" Value="True" />
    </DataTrigger>
  </DataTemplate.Triggers>
</DataTemplate>