อยากได้ textbox รับค่าตามที่กำหนดครับ....รับค่าที่เป็นตัวเลข(ไม่ทราบว่า IsDigit กับ IsNumber ต่างกันยังไง)

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar == (char)Keys.Back)
            {
                m_Amount = Convert.ToDouble(textBox1.Text);
                m_Amount = ((m_Amount * 100) - ((m_Amount * 100) % 10)) / 1000;
                textBox1.Text = m_Amount.ToString("#,##0.00 ;#,##0.00-");
                textBox1.SelectionStart = textBox1.SelectionStart + textBox1.Text.Length;
            }
            else
            {
                e.Handled = true;
                if (e.KeyChar >= (char)48 && e.KeyChar <= (char)57)
                {
                    if (textBox1.Text.Length > 10)
                    {
                        e.Handled = false;
                        return;
                    }
                    m_Amount = Convert.ToDouble(textBox1.Text);
                    m_AmountNew = Convert.ToDouble(e.KeyChar.ToString());
                    m_Amount = ((m_Amount * 1000) + m_AmountNew) / 100;
                    textBox1.Text = m_Amount.ToString("#,##0.00 ;#,##0.00-");
                    textBox1.SelectionStart = textBox1.SelectionStart + textBox1.Text.Length;
                }
                else if (e.KeyChar == (char)8)
                {
                    m_Amount = Convert.ToDouble(textBox1.Text);
                    m_Amount = ((m_Amount * 100) - ((m_Amount * 100) % 10)) / 1000;
                    textBox1.Text = m_Amount.ToString("#,##0.00 ;#,##0.00-");
                    textBox1.SelectionStart = textBox1.SelectionStart + textBox1.Text.Length;
                }
            }
           
        }