Form1 放置 listBox1, button1, textBox1

textBox1 输入关键字，按 button1 ，关键字在 listBox1 中高亮为红色

        private void Form1_Load(object sender, EventArgs e)
        {
            listBox1.DrawMode = DrawMode.OwnerDrawFixed;
            listBox1.Items.Add("News today");
            listBox1.Items.Add("News yesterday");
        }

        private void button1_Click(object sender, EventArgs e)
        {
            listBox1.Refresh();
        }

        private void listBox1_DrawItem(object sender, DrawItemEventArgs e)
        {
            //
            // Draw the background of the ListBox control for each item.

            e.DrawBackground();

            string keyWords = textBox1.Text;

            string text = ((ListBox)sender).Items[e.Index].ToString();

            List<int> keyWordIndexes = new List<int>();

            //Keywords match
            if (!string.IsNullOrEmpty(keyWords))
            {
                int index = 0;
                while (index >= 0)
                {
                    index = text.IndexOf(keyWords, index);

                    if (index >= 0)
                    {
                        keyWordIndexes.Add(index);
                        index += keyWords.Length;
                    }
                }
            }

            //If no keywords matched show black color
            if (keyWordIndexes.Count == 0)
            {
                e.Graphics.DrawString(text, e.Font, Brushes.Black,
                    e.Bounds, StringFormat.GenericDefault);
                e.DrawFocusRectangle();
                return;
            }

            //Draw
            //Keywords red color

            int start = 0;
            float x = 0;
            float y = e.Bounds.Y;

            foreach (int i in keyWordIndexes)
            {
                string normal = text.Substring(start, i - start);

                e.Graphics.DrawString(normal, e.Font, Brushes.Black,
                    x, y);
               
                x += e.Graphics.MeasureString(normal, e.Font).Width;

                string key = text.Substring(i, keyWords.Length);

                e.Graphics.DrawString(key, e.Font, Brushes.Red,
                    x, y);

                x += e.Graphics.MeasureString(key, e.Font).Width;

                start = i + keyWords.Length;
            }

            if (start < text.Length)
            {
                string normal = text.Substring(start, text.Length - start);

                e.Graphics.DrawString(normal, e.Font, Brushes.Black,
                    x, y);

            }

            e.DrawFocusRectangle();

        }