TextBox输入限制

1.只能输入数字：
        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!(((e.KeyChar >= '0') && (e.KeyChar <= '9')) || e.KeyChar <= 31))
            {
                if (e.KeyChar == '.')
                {
                    e.Handled = true;
                }
                else
                    e.Handled = true;
            }
            else
            {
                if (e.KeyChar <= 31)
                {
                    e.Handled = false;
                }
                else if ((e.KeyChar >= '0') && (e.KeyChar <= '9'))
                {
                    if (((TextBox)sender).Text.ToString() != "")
                    {
                        if (Convert.ToDouble(((TextBox)sender).Text) == 0)
                        {
                            if (((TextBox)sender).Text.Trim().IndexOf('.') > -1)
                            {
                                e.Handled = false;
                            }
                            else
                            {
                                e.Handled = true;
                            }
                        }
                    }
                    else
                    {
                        e.Handled = false;
                    }
                }
            }
        }
2.只能输入小数
        private void textBox2_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!(((e.KeyChar >= '0') && (e.KeyChar <= '9')) || e.KeyChar <= 31))
            {
                if (e.KeyChar == '.')
                {
                    if (((TextBox)sender).Text.Trim().IndexOf('.') > -1 || ((TextBox)sender).Text.Trim() == "")
                        e.Handled = true;
                }
                else
                    e.Handled = true;
            }
            else
            {
                if (e.KeyChar <= 31)
                {
                    e.Handled = false;
                }
                else if ((e.KeyChar >= '0') && (e.KeyChar <= '9'))
                {
                    if (((TextBox)sender).Text.ToString() != "")
                    {
                        if (Convert.ToDouble(((TextBox)sender).Text) == 0)
                        {
                            if (((TextBox)sender).Text.Trim().IndexOf('.') > -1)
                            {
                                e.Handled = false;
                            }
                            else
                            {
                                e.Handled = true;
                            }
                        }
                    }
                    else
                    {
                        e.Handled = false;
                    }
                }
            }
        }
3.单引号用"`"来代替：
        private void textBox3_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar == Convert.ToChar("'"))
            {
                ((TextBox)sender).Text = ((TextBox)sender).Text + "`";
                ((TextBox)sender).SelectionStart = Convert.ToInt32(((TextBox)sender).Text.Length);
                e.Handled = true;
            }
        }