if (richTextBox1.Text.Contains(txtFind.Text))
{
string[] s = richTextBox1.Text.Split(new string[] { txtFind.Text }, StringSplitOptions.None);
int len = 0; //起始长度变量
for (int i = 0; i < s.Length; i++)
{
len += s[i].Length;
richTextBox1.SelectionStart = len + i * txtFind.Text.Length;
richTextBox1.SelectionLength = txtFind.Text.Length;
richTextBox1.SelectionColor = Color.Red;
}
}
else
{
MessageBox.Show("error");
}