Edo Gasali said:

@tbetts1982 After some consideration, finally I am now using UltraFormattedTextEditor as you suggest as workaround mate.

Thanks for your idea.

You're welcome. The amount of code necessary to make the formatted editor a decent editor for users like that dialog would cause any programmer a headache. It's much easier to use the dialog than to reinvent the wheel. If they really intended users to click a button to open the dialog for editing an already editable textbox, why not cut out the middle man and work out a solution to combine the functionality of the dialog into their user control?

@tbetts1982 After some consideration, finally I am now using UltraFormattedTextEditor as you suggest as workaround mate.

Thanks for your idea.

Hey, I really do appreciate your help mate!
However I have did another workaround, resetting the text style in override method OnFontChanged().
Basically it just clear and re-write the text.
Sounds not a good way, but it works well without performance issue.

Thanks for your help!

This might not be the necessary answer you're looking for, but I did have fun hacking away at the WinFormattedTextEditor. When you're in the design view they give you this really nice editor for the value of that text editor, so I thought it would be nice to use that on a form as well. Here's my insane results, with Office 2007 color scheming!

You can really put that editor into any container. In this example I used the form's fill panel since I made use of the WinFormManager, but you can shove it into any panel you want.

Office2007ColorTable.ColorScheme = Office2007ColorScheme.Black;
Infragistics.Win.SupportDialogs.FormattedTextEditor.FormattedTextUIEditorForm editor_form = new Infragistics.Win.SupportDialogs.FormattedTextEditor.FormattedTextUIEditorForm();
editor_form = new Infragistics.Win.SupportDialogs.FormattedTextEditor.FormattedTextUIEditorForm(ultraFormattedTextEditor1);
editor_form.TopLevel = false;
editor_form.FormBorderStyle = FormBorderStyle.None;
editor_form.Dock = DockStyle.Fill;
editor_form.Visible = true;
Infragistics.Win.UltraWinToolbars.UltraToolbarsManager top_toolmanager = Infragistics.Win.UltraWinToolbars.UltraToolbarsManager.FromForm(editor_form);
top_toolmanager.Style = Infragistics.Win.UltraWinToolbars.ToolbarStyle.Office2007;
foreach (Control editor_control in editor_form.Controls)
{
    switch (editor_control.Name)
    {
        case "pnlButtons":
            if (editor_control.Name == "pnlButtons")
                editor_control.Visible = false;
            break;
        case "ultraTabControl1":
            ((Infragistics.Win.UltraWinTabControl.UltraTabControl)editor_control).ViewStyle = Infragistics.Win.UltraWinTabControl.ViewStyle.Office2007;
            break;
    }
}
Form1_Fill_Panel.ClientArea.Controls.Add(editor_form);

This reply post was more of a for fun one, but if you have any questions about what I did above or how to change something, let me know.

I am looking around on UltraFormattedTextEditor finding the way to create multiple color in the text. Does it support multiple color in a textbox?
On my previous sample project it just show a color, but on the actual I need it to support multiple color. That's the reason I use RichTextBox which support multiple text style in one place :)

Does anyone here have solution?
I've found another person having the same problem last year and he doesn't get answered: http://community.infragistics.com/forums/p/47540/253744.aspx#253744
Works around for multiple color in textbox is acceptable.

Thanks.