验证textbox输入的是否是数字，包括小数

public bool isnumeric(string str)

        {

            int count = 0;

            if (str.Trim() == "" || str.Trim().Length == 0)

            {

                return false;

            }

            else

            {

                char[] ch = new char[str.Length];

                ch = str.ToCharArray();

                for (int i = 0; i < ch.Length; i++)

                {

                    if (!char.IsNumber(ch[i]) && ch[i] != '.')

                    {

                        return false;

                    }

                    if (ch[i]=='.')

                    {

                        count++;

                        if (i == 0 || i == ch.Length - 1)

                            return false;

                    }

                }

                if (count > 1)

                    return false;

                return true;

            }                     

        }