static bool IsNumeric(string str)
  {
   if (str==null || str.Length==0)
    return false;
   foreach(char c in str)
   {
    if (!Char.IsNumber(c))
    {
     return false;
    }
   }
   return true;
  }

    方法二:
private bool IsNumeric(string s)

         {

              char ch0 = '0';

              char ch9 = '9';

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

              {

                  if ((s[i] < ch0 || s[i] > ch9))

                   {

                         this.lblwarning.Text="此处应输入整数且非负！";

                         return false;

                   }

              }

              return true;

         }

以上两种方法都只能验证字符串是否为整数，不能验证小数，一下两种方法就解决了这个问题。

方法三:

static bool IsNumeric (string str)
{  
   System.Text.RegularExpressions.Regex reg1 
       = new System.Text.RegularExpressions.Regex(@"^[-]?\d+[.]?\d*$"); 
   return reg1.IsMatch(str);
}

方法四：

public static bool IsConvert(string Expression,Type DataType)

{

  switch(DataType.Name)

  {

       case "Double":

              try

              {

                     Double.Parse(Expression);

                     return true;

              }

              catch

              {

                     return false;

              }

       case "DateTime":

              try

              {

                     DateTime.Parse(Expression);

                     return true;

              }

              catch

              {

                     return false;

              }

       default:

              return true;

  }

}