C# WPF: Changing color of Text upon Character Detection

Question

I'm writing a Console for users, so that they can write code in it similar to Visual Studio. I was wondering how to change the color of a set of text in a WPF TextBox as soon as the program detects the input of a certain character, such as the /* */ comment tags.

When a user enters a /* tag, the text after the tag should be colored in green and when the users closes the tags, the texts should turn back to white. I tried doing this with the TextChanged method but I don't know how to proceed.

('console' is the TextBox in my Window)

private void console_TextChanged(object sender, TextChangedEventArgs e)
{
      if (e.Changes.Equals("/*"))
      {
             console.Foreground = Brushes.Green;
      }
}

console_TextChanged means that when you type text and focus out of the textbox then it will be called. You should use KeyPress event instead. — Lucassith, May 06 '15 at 13:25
I see. But even if I use KeyPress, I'd have to scan the previously typed text to see if the 'currently typing' text is within comment tags, mate. How can I do that? @Lucassith — Jay, May 06 '15 at 13:29
http://stackoverflow.com/questions/14085607/textbox-text-color-change identical question although there is no good answer. — Lucassith, May 06 '15 at 13:42
I saw that @Lucassith but it doesn't provide a proper answer for the question — Jay, May 06 '15 at 14:11

score 0 · Accepted Answer · answered May 06 '15 at 14:49

You cannot use TextBox to change some specific portion of color. In this case you need RichTextBox. You use the PreviewTextInput event to get the typed text/char. I have written some logic to make the foreground of the RichTextBox change when typing specific char. I think you can build your logic one top of this code.

 <RichTextBox x:Name="rtb" Width="200" Height="200" PreviewTextInput="rtb_PreviewTextInput"/>

 public partial class MainWindow : Window
{
    string prevText=string.Empty;
    TextPointer start;
    public MainWindow()
    {
        InitializeComponent();            
    }      
    private void rtb_PreviewTextInput(object sender, TextCompositionEventArgs e)
    {
        if (e.Text.Equals("*") && (prevText.Equals("/")))
        {
            start = rtb.CaretPosition;
            TextPointer end = rtb.Document.ContentEnd;
            TextRange range = new TextRange(start, end);
            range.ApplyPropertyValue(RichTextBox.ForegroundProperty, Brushes.Green);
        }
        if (e.Text.Equals("/") && (prevText.Equals("*")))
        {                
            TextPointer end = rtb.CaretPosition; 
            TextRange range = new TextRange(start, end);
            range.ApplyPropertyValue(RichTextBox.ForegroundProperty, Brushes.Red);
        }
        prevText = e.Text;
    }        
}

Hey this is a great start! However the start of comment tag /* malfunctions a bit, the green doesn't show up. Any idea why? — Jay, May 06 '15 at 16:15
I thought of giving idea in which you can improve.. May be complete logic might some time... — Ayyappan Subramanian, May 06 '15 at 16:23
Currently when you add some text then if you place /* inbetween the text it will change font green to the rest of the text — Ayyappan Subramanian, May 06 '15 at 16:24
Hey thanks again for taking the time. I'll play around it a bit and see what I can do. I'll select your answer now but if you have the time and you come up with a better code please email it to me, mate :) dinukawylde@gmail.com. Thank you sir. — Jay, May 06 '15 at 16:28
Only problem is having to add the tag later to see the color. How can I modify the code such that it changes the color as soon as the /* is entered, Ayyappan? — Jay, May 06 '15 at 16:56

C# WPF: Changing color of Text upon Character Detection

1 Answers1