使用撤消和重做命令更改RichTextBox工具栏颜色

Question

1- Run following code.

<Window x:Class="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">

<StackPanel>
    <ToolBar>
        <Button x:Name="UndoButton" Width="30" CommandTarget="{Binding ElementName=RichTextBox1}" Command="ApplicationCommands.Undo">
            <TextBlock x:Name="UndoTextBlock" Foreground="Gray" FontFamily="Wingdings 3" FontSize="24" Text="Q"/>
        </Button>

        <Button x:Name="RedoButton" Width="30" CommandTarget="{Binding ElementName=RichTextBox1}" Command="ApplicationCommands.Redo">
            <TextBlock x:Name="RedoTextBlock" Foreground="Gray" FontFamily="Wingdings 3" FontSize="24" Text="P"/>
        </Button>
    </ToolBar>

    <RichTextBox x:Name="RichTextBox1">
        <FlowDocument>
            <Paragraph>
                <Run Text="Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum."/>
            </Paragraph>
        </FlowDocument>
    </RichTextBox>
</StackPanel>

</Window> 

2- Check if UndoButton is highlighted when you put your mouse on the UndoButton.

3- Delete some text from opening window.

4- Check if UndoButton is highlighted when you put your mouse on the UndoButton.

5- As you can see if you delete some text then UndoButton is highlighted when you put your mouse on the UndoButton

My question is here;

I want to change Foreground color of UndoTextBlock from Gray to Green when User delete some text (when UndoButton is active).

Answer 1

I think can handle the TextChanged event of RichTextBox1.

First, get the original content from RichTextBox.

Then, compare the original content with the new content.

If the content has changed, change the Foreground colour for undoTextBlock to Green.

    private void RichTextBox1_OnTextChanged(object sender, TextChangedEventArgs e)
    {
        var textRange = new TextRange(RichTextBox1.Document.ContentStart,RichTextBox1.Document.ContentEnd);
        var text = textRange.Text;

        if (string.IsNullOrEmpty(text.Trim()))
            return;

        if (!_loaded)
        {
            _orginalContent = text;
            _loaded = true;
        }

        var newContent = text;
        if (newContent == _orginalContent)
            UndoTextBlock.Foreground = Brushes.Gray;
        else
            UndoTextBlock.Foreground = Brushes.Green;
    }