On the surface, the C1RichTextBox control appears just like a standard TextBox. It provides the same properties to control the font, colors, text, and selection. That can be an advantage – if you have an application that uses TextBox controls, you may be able to simply replace them with C1RichTextBox controls without any additional changes.

For example, the following code implements a simple search-and-replace routine that works on TextBox and on C1RichTextBox controls:

To write the code in Visual Basic:

Private Sub SearchAndReplace(tb As TextBox, find As String, replace As String)
    Dim start As Integer = 0
    While True
        Dim pos As Integer = tb.Text.IndexOf(find, start)
        If pos < 0 Then
            Exit While
        End If
        tb.[Select](pos, find.Length)
        ' Optionally show a dialog box to confirm the change.
        tb.SelectedText = replace
        start = pos + 1
    End While
End Sub

To write the code in C#:

void SearchAndReplace(TextBox tb, string find, string replace)
{
  for (int start = 0; ; )
  {
    int pos = tb.Text.IndexOf(find, start);
    if (pos < 0) break;
    tb.Select(pos, find.Length);
    // Optionally show a dialog box to confirm the change.
    tb.SelectedText = replace;
    start = pos + 1;
  }
}

The code looks for matches in the C1RichTextBox.Text property. It selects each match using the C1RichTextBox.Select method, and then replaces the text using the SelectedText property. To convert this method for use with the C1RichTextBox control, you would simply change the type of the first argument to use a C1RichTextBox instead of a regular TextBox.

This is what the C1RichTextBox has in common with the regular TextBox. But of course it goes way beyond that. Suppose you wanted to highlight the replacements with a yellow background. This would be impossible with a regular TextBox. With the C1RichTextBox, you could accomplish that with one additional line of code:

To write the code in Visual Basic:

Private Sub SearchAndReplace(tb As C1RichTextBox, find As String, replace As String)
    Dim start As Integer = 0
    While True
        Dim pos As Integer = tb.Text.IndexOf(find, start)
        If pos < 0 Then
            Exit While
        End If
        tb.[Select](pos, find.Length)
        ' Optionally show a dialog box to confirm the change.
        tb.Selection.InlineBackground = New SolidColorBrush(Colors.Yellow)
        tb.SelectedText = replace
        start = pos + 1
    End While
End Sub

To write the code in C#:

void SearchAndReplace(C1RichTextBox tb, string find, string replace)
{
  for (int start = 0; ; )
  {
    int pos = tb.Text.IndexOf(find, start);
    if (pos < 0) break;
    tb.Select(pos, find.Length);
    // Optionally show a dialog box to confirm the change.
    tb.Selection.InlineBackground = new SolidColorBrush(Colors.Yellow);
    tb.SelectedText = replace;
    start = pos + 1;
  }
}

The C1RichTextBox.Selection property provides properties that allow you to inspect and modify the formatting of the current selection. With this property and the ones in common with the TextBox control, you can easily create documents and add rich formatting.

You could use the technique described above to implement a toolbar or to add syntax coloring to documents. These topics are described in more detail in later sections.