Format richtextbox without selection

Question

I want to change the formatting in a richtextbox in two ways:

• text is selected => text should re-size. This works fine.
• text is not selected, just a caret cursor is set between a text. => font-size should change for further writing. It shouldn't change the already existing text before => this don't work.

Example for my second requierement: My richtextbox got the text

stackoverflow

and the caret cursor is between stackover and flow like this:

stackover|flow

Now I need to change the fontsize on the current caret position for example to 20. On further writing I just want the text on this position displayed bigger. I don't want to change the current existing text. Like:

stackovercoolflow

cool should be in fontsize 20 now and stackover flow in default font size (like before)

I found a lot of answers but nothing of them helped me.

Most hints were:

• Focus() on richtextbox
• Use Selection.Start and Selection.End
• Use an own method for 'SetFontSize'

But nothing of them worked for me...

Mostly I oriented myself on the following question wpf-richtextbox-fontface-fontsize

Currently I ended up with the followed code, but it only changes text-selection.

<Window x:Class="WpfApp2.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"
    mc:Ignorable="d"
    Title="MainWindow" Height="450" Width="800">
<StackPanel Orientation="Vertical">
    <RichTextBox Height="300" Width="300" x:Name="MyRichTextBox" />
    <ComboBox Width="300" x:Name="cmbbx" SelectedIndex="1" SelectionChanged="ComboBox_SelectionChanged" />
</StackPanel>

using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;

namespace WpfApp2
{
    public partial class MainWindow : Window
    {
        public ObservableCollection<double> Werte { get; set; }

        public MainWindow()
        {
            Werte = new ObservableCollection<double>();
            Werte.Add(4);
            Werte.Add(10);
            Werte.Add(20);
            Werte.Add(55);
            InitializeComponent();

            cmbbx.ItemsSource = Werte;
        }


        private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            var newSize = (double)cmbbx.SelectedValue;
            TextRange r = new TextRange(MyRichTextBox.Selection.Start, MyRichTextBox.Selection.End);
            r.ApplyPropertyValue(TextElement.FontSizeProperty, newSize);
        }

    }
}

This just changes text-selection. There is no formatting when nothing is selected (just cursor is set). I am working with .net 5

Answer 1

Probably you want something like below:

<Window x:Class="WpfApp2.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"        
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>            
        </Grid.RowDefinitions>
        <ComboBox Grid.Row="0" Width="60" x:Name="cmbbx" SelectedIndex="1" SelectionChanged="ComboBox_SelectionChanged" HorizontalAlignment="Left"/>        
        <RichTextBox Grid.Row="1" x:Name="rtb" AllowDrop="True" VerticalScrollBarVisibility="Auto" Padding="2"                    
                     SelectionChanged="rtb_SelectionChanged"
                     TextChanged="rtb_TextChanged">
            <FlowDocument/>
        </RichTextBox>       
    </Grid>
</Window>

using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Collections.ObjectModel;

namespace WpfApp2
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            var Werte = new ObservableCollection<double> { 4, 10, 16, 20, 26, 55 };

            InitializeComponent();
            cmbbx.ItemsSource = Werte;
        }
       
        private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (!rtb.Selection.IsEmpty)
            {
                if (cmbbx.SelectedValue is double newSize)
                {                   
                    var range = new TextRange(rtb.Selection.Start, rtb.Selection.End);
                    range.ApplyPropertyValue(TextElement.FontSizeProperty, newSize);
                }
            }           
        }    

        // Use `TextChanged` event to apply the currently selected font size to the entered text
        private void rtb_TextChanged(object sender, TextChangedEventArgs e)
        {
            // Disable recursive calling this event handler 
            rtb.TextChanged -= rtb_TextChanged;

            foreach (var change in e.Changes)
            {
                if (cmbbx != null)
                {
                    TextPointer tp = rtb.Document.ContentStart.GetPositionAtOffset(change.Offset);
                    var range = new TextRange(tp, tp.GetPositionAtOffset(1, LogicalDirection.Backward));
                    if (!string.IsNullOrEmpty(range.Text) && cmbbx.SelectedValue is double fontsize)
                    {
                        range.ApplyPropertyValue(TextElement.FontSizeProperty, fontsize);
                    }
                }
            }
            // Restore the event handler
            rtb.TextChanged += rtb_TextChanged;          
        }

        // The following `SelectionChanged` event handler is used to set a font size in the combobox 
        // depend on the current caret location.
        private void rtb_SelectionChanged(object sender, RoutedEventArgs e)
        {            
            if (rtb.Selection is TextSelection selection)
            {
                if (selection.GetPropertyValue(TextElement.FontSizeProperty) is double fsize)
                {
                    foreach (var it in cmbbx.Items)
                    {
                        if ((double)it == fsize)
                        {
                            // The currently selected document fragment is containing font with size presented in the ComboBox
                            cmbbx.SelectedItem = it;
                            return;
                        }
                    }                  
                }
                // The currently selected document fragment contains fonts 
                // with different font sizes or the font size doesn't included to the the combobox 
                cmbbx.SelectedItem = null;
            }
        }
    }
}

I added some notes in the code above. Let me know if an additional descriptions are required.