Find and highlight word in Windows Forms RichTextBox using C# and VB.Net

Hi aginell4life,

Refer below sample.

I have added a TextBox, a Button and a RichTextBox control to the Form.

Namespaces

C#

using System.Linq;
using System.Collections.Generic;

VB.Net

Imports System.Linq
Imports System.Collections.Generic

Code

C#

private void Form1_Load(object sender, EventArgs e)
{
    richTextBox1.Text = "Writing about yourself can seem embarrassing at first. " +
                        "Cover letters, personal essays, and bio notes about yourself come with some " +
                        "specific tricks and tips that can make it a lot less intimidating when choosing style and content. " +
                        "Learn the basics and you will be able to make your personal writing stand out";
    txtWord.Text = "will";
}

public void hl(RichTextBox T, string Word, Color color1)
{
    T.Text = "Writing about yourself can seem embarrassing at first. " + 
        "Cover letters, personal essays, and bio notes about yourself come with some " + 
        "specific tricks and tips that can make it a lot less intimidating when choosing style and content. " + 
        "Learn the basics and you will be able to make your personal writing stand out";
    List<string> statements = richTextBox1.Text.Split('.').ToList();
    for (int j = statements.Count - 1; j >= 0; j += -1)
    {
        if (!statements[j].Trim().ToLower().Contains(txtWord.Text.ToLower().Trim()))
            statements.RemoveAt(j);
    }
    T.Text = string.Join(".", statements);

    int pos = 0;
    string s = T.Text;
    int i = 0;
    bool StopWhile = false;
    while (!StopWhile)
    {
        int j = s.IndexOf(Word, i);
        if (j < 0)
            StopWhile = true;
        else
        {
            T.Select(j, Word.Length);
            T.SelectionColor = color1;
            T.SelectionBackColor = Color.Yellow;
            i = j + 1;
        }
    }
    T.Select(pos, 0);
}

private void btnHighlight_Click(object sender, EventArgs e)
{
    hl(richTextBox1, txtWord.Text, Color.Red);
}

VB.Net

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    richTextBox1.Text = "Writing about yourself can seem embarrassing at first. " +
                        "Cover letters, personal essays, and bio notes about yourself come with some " +
                        "specific tricks and tips that can make it a lot less intimidating when choosing style and content. " +
                        "Learn the basics and you will be able to make your personal writing stand out"
    txtWord.Text = "will"
End Sub

Public Sub hl(ByVal T As RichTextBox, ByVal Word As String, ByVal color1 As Color)

    T.Text = "Writing about yourself can seem embarrassing at first. " +
                        "Cover letters, personal essays, and bio notes about yourself come with some " +
                        "specific tricks and tips that can make it a lot less intimidating when choosing style and content. " +
                        "Learn the basics and you will be able to make your personal writing stand out"
    Dim statements As List(Of String) = richTextBox1.Text.Split("."c).ToList()
    For j As Integer = statements.Count - 1 To 0 Step -1
        If Not statements(j).Trim().ToLower().Contains(txtWord.Text.ToLower().Trim()) Then
            statements.RemoveAt(j)
        End If
    Next
    T.Text = String.Join(".", statements)

    Dim pos As Integer = 0
    Dim s As String = T.Text
    Dim i As Integer = 0
    Dim StopWhile As Boolean = False
    While Not StopWhile
        Dim j As Integer = s.IndexOf(Word, i)
        If j < 0 Then
            StopWhile = True
        Else
            T.Select(j, Word.Length)
            T.SelectionColor = color1
            T.SelectionBackColor = Color.Yellow
            i = j + 1
        End If
    End While
    T.Select(pos, 0)
End Sub

Private Sub btnHighlight_Click(sender As Object, e As EventArgs) Handles btnHighlight.Click
    hl(richTextBox1, txtWord.Text, Color.Red)
End Sub

Screenshot