Highlight Part of TextBox Text in .Net Windows Form

Question

Requirement

I am using Vistual Studio 2005. I need Textbox which

• Should support Japanese language. User should be able to paste Japanese text in textbox.
• Text in textbox should always be Bold.
• Text after 100 characters should be highlighted in Yellow color when user is typing.
• Textbox should not allow any other formatted text.

Solution I tried

1. Normal Textbox with FontStyle set to Bold.
   Issue : I can paste Japanese text and text always remains BOLD. Only issue is textbox does not support highlighting of text as user types.

2. RichTextBox : Highlight text in TextChanged eventhandler.

   handler = new System.EventHandler(richTextBox1_TextChanged);
   
   private void richTextBox1_TextChanged(object sender, EventArgs e)
   {
       this.richTextBox1.TextChanged -= this.handler;
       int index = richTextBox1.SelectionStart;
   
       richTextBox1.Select(0, richTextBox1.Text.Length);
       richTextBox1.SelectionBackColor = Color.White;
       richTextBox1.SelectionLength = 0;
   
       if (richTextBox1.Text.Length > 100)
       {
           richTextBox1.Select(100, richTextBox1.Text.Length);
           richTextBox1.SelectionBackColor = Color.Yellow;
           richTextBox1.SelectionLength = 0;
       }
   
       richTextBox1.SelectionStart = index;
       this.richTextBox1.TextChanged += this.handler;
   }
   

   Highthing works fine. But there are following issues.

   • When I copy paste Japanese text into richtextbox, it is shown as Squre boxes. But if I assign same japanese text programmatically, it is displayed correctly. Even in normal textbox the pasted text is shown correctly. So not sure what is the problem with richtextbox.

   • I could not disable formatting of richtextbox. e.g. If I copy some html text with hyperlinks and paste in richtextbox, I see the hyperlinks. And my requriment says NO formatting except BOLD is allowed.

I want to acheive this functionality using windows form controls. Third party control would be my last option.

Can someone help?

Thanks in Advance!

~Sambha

Answer 1

I got one solution, but not sure if this is the efficient way of doing it and if it will cause some other issues.

Solution : Create subclass from RichTextBox and ovverride KeyDown event. Check if Ctrol+V or Shift+Inst key was pressed, call paste method using DataFormats.UnicodeText.

class MyRichTextBox : RichTextBox
{

protected override void OnKeyDown(KeyEventArgs e)
{
    switch (e.KeyData)
    {
        case (Keys.Shift | Keys.Insert): 
        case (Keys.Control | Keys.V):

            this.Paste(DataFormats.GetFormat(DataFormats.UnicodeText));
            e.SuppressKeyPress = true;

            return;
    }

    base.OnKeyDown(e);
}

}