You have a numeric type variable, which will hold a numeric value obtained from a database. The database may return this value as null. You need a simple, clean way to store this numeric value, even if it is returned as null.
Use a
nullablevalue type. There are two ways of creating a nullable value type. The first way is to use the ? type modifier:
In addition, testing the nullable type can be done in
One of two ways. First, by using the HasValue property as shown here:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="NullableType.aspx.cs" Inherits="NullableType" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<table border="1">
<tr>
<td>
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
</td>
<td>
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" /></td>
</tr>
</table>
</div>
</form>
</body>
</html>
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class NullableType : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Button1_Click(object sender, EventArgs e)
{
//Essentially both of the following statements are equivalent:
int? myDBInt = null;
Nullable<int> myDBInt = new Nullable<int>();
if (myDBInt.HasValue)
Label1.Text = "Has a value: " + myDBInt.Value;
else
Label1.Text = "Does not have a value (NULL)";
}
}