C# RichTextbox的字体格式和颜色

【关于字体格式】

设置的是第一个字符的颜色，这时richtextBox的rtf中记录下位置0的颜色，重置text时，在rtf中的位置从位置0开始,因此颜色还是Color.Red,第三次也应该同样如此
richTextBox1.Text = "123";
richTextBox1.Select(0, 1);
richTextBox1.SelectionColor = Color.Red;
richTextBox1.Clear();//清除文本，包括样式
//或richTextBox1.Text="";
richTextBox1.Text = "abc";
richTextBox1.Text = "efg";
这样重置后的文本颜色就会是黑色.

【关键字着色】

publicpartialclass RichTextBox : Form
    ...{
        public RichTextBox()
        ...{
             InitializeComponent();
         }

        privatevoid tSql_TextChanged(object sender, EventArgs e)//文本框改变事件
        ...{
            int index=this.tSql.SelectionStart;   //记录修改的位置
            this.tSql.SelectAll();
            this.tSql.SelectionColor= Color.Black;
string[] keystr=...{"select", "from","where"," and"," or"," order"," by"," desc"," when"," case",
   " then ", " end"," on"," in"," is"," else"," left"," join"," not"," null" };
            for (int i = 0; i < keystr.Length; i)
                this.getbunch(keystr[i],this.tSql.Text);

            this.tSql.Select(index,0);    //返回修改的位置
            this.tSql.SelectionColor= Color.Black;

         }
        publicint getbunch(string p,string s)//给关键字上色
        ...{
            int cnt=0;int M= p.Length;int N = s.Length;
            char[] ss= s.ToCharArray(), pp= p.ToCharArray();
            if (M> N) return 0;
            for (int i = 0; i < N- M1; i)
{
                int j;
                for (j=0; j< M; j)
                ...{
                    if (ss[ij]!= pp[j])break;
                 }
                if (j== p.Length)
                ...{
                    this.tSql.Select(i, p.Length);
                    this.tSql.SelectionColor= Color.Blue;
                     cnt;
                 }
}
            return cnt;

         }

     }

【绘制颜色提议】

最好的做法是继承RichTextBox，重载新类的Paint方法。

并且在设置SelectionLength的时候，禁止控件的重绘过程，这样才不会出现被语法高亮的文本有一个突然选中的过程。
以下2个方法将会对你解决这一问题有很大的帮助.
[DllImport("user32")]
private static extern int SendMessage(IntPtr hwnd, int wMsg, int wParam, IntPtr lParam);
private const int WM_SETREDRAW = 0xB;

//停止控件的重绘
private void BeginPaint()
{
SendMessage(yourRichTextBox.Handle, WM_SETREDRAW, 0, IntPtr.Zero);
}
//允许控件重绘.
private void EndPaint()
{
SendMessage(yourRichTextBox.Handle, WM_SETREDRAW, 1, IntPtr.Zero);
yourRichTextBox.Refresh();
}