Question

I have a TabControl with TextBox controls in the ContentTemplate. When I type some text in one tab and switch to another tab, the Undo history in the original tab is gone when I go back.

Another problem that comes up is any text that was selected is deselected and the caret moves to the beginning of the TextBox.

If I make a window with just hardcoded TabItem controls, the undo history is preserved. The issue has something to do with my binding or templates.

Here is my XAML for the main window

<Window x:Class="TabbedTextAreaTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="auto"/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Button Command="{Binding AddNewTab}">Add Tab</Button>
        <TabControl ItemsSource="{Binding Tabs}" Grid.Row="1">
            <TabControl.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Header}"/>
                </DataTemplate>
            </TabControl.ItemTemplate>
            <TabControl.ContentTemplate>
                <DataTemplate>
                    <TextBox Text="{Binding Content, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
                </DataTemplate>
            </TabControl.ContentTemplate>
        </TabControl>
    </Grid>
</Window>

Is there a way to preserve the undo/redo history and selected text when switching tabs without manually catching those commands?

Answer 1

When you use a TabControl which gets its tabs via databinding on ItemsSource, WPF doesn’t keep the visual tree for each item around as you switch. Thus, when you switch from tab 1 to tab 2, then back to tab 1, the controls on tab 1 are not actually the same control instances which you saw on tab 1 the first time.

There are a number of ways around to deal with this – TabControls which have explicit TabItem instances do keep their visual trees when you switch tabs, so probably the easiest way to do it is to wrap your collection of tab items in something which makes TabItems for them.

Unfortunately right now I can’t find a link to an example of how to do this. There are references to articles elsewhere on SO, but they all seem to point to pages which no longer exist, and I don’t have time to dig any deeper.