windows forms RichTextBox 控件中不显示所选文本

Question

For some reason I have to use a Windows.Forms. RichTextBox control within my WPF Window:

<Window x:Class="TestSelectionRTBDansWPF.MainWindow"
        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"
        xmlns:wf="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms"
        xmlns:local="clr-namespace:TestSelectionRTBDansWPF"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid Margin="10">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Button x:Name="btnSelect" Content="Select 10 first characters" Padding="10" Margin="0 0 0 10" Width="160" Click="BtnSelect_Click"/>
        <WindowsFormsHost Grid.Row="1">
            <wf:RichTextBox x:Name="rtb" Dock="Fill" Text="Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis non mauris id ipsum auctor vehicula sed ut felis. Donec porttitor nisi eget ex porttitor, sed posuere sapien pretium."/>
        </WindowsFormsHost>
    </Grid>
</Window>

At some point, I wan't to select text in my RichTextBox from another thread:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void BtnSelect_Click(object sender, RoutedEventArgs e)
    {
        Thread th = new Thread(() =>
        {
            Thread.Sleep(2000);
            SelectText(0, 10);
        });
        th.Start();
    }

    delegate void ParametrizedMethodInvoker5(int arg1, int arg2);
    public void SelectText(int start, int length)
    {
        if (!Dispatcher.CheckAccess())
        {
            Dispatcher.Invoke(new ParametrizedMethodInvoker5(SelectText), start, length);
            return;
        }
        rtb.SelectionStart = start;
        rtb.SelectionLength = length;
        MessageBox.Show("Selection done!\nSelected text: " + rtb.SelectedText);
    }
}

The message box correctly displays selected text, but nothing is highlighted in the displayed RichTextBox control. EDIT: when using mouse or keyboard, selection works perfectly fine.

While writing this post, I realized that adding a reference to System.Drawing and setting the rtb.SelectionBackColor property do the trick, though it looks more like a patch than a real solution for I will have to handle SelectionChanged to reset the background color of previous selected text.

Has anyone any clues on this?

Answer 1

The selection works but the RichTextBox has not the focus. You can simply set the focus to the RichTextBox via rtb.Focus(); after selecting or focus the control manually via the tab key.