Creating a Numeric Up/Down Control with a Web Service Backend (VB)
Instead of letting a user type a value into a check box, a numeric up/down control (that exists on Windows and other operating systems) could prove as more comfortable. By default, the NumericUpDown control always increases or decreases a value by 1, but a web service proves more flexibility.
Overview
Instead of letting a user type a value into a check box, a numeric up/down control
(that exists on Windows and other operating systems) could prove as more comfortable.
By default, the NumericUpDown control always increases or decreases a value by 1,
but a web service proves more flexibility.
Steps
The ASP.NET AJAX Control Toolkit contains the NumericUpDown extender which automatically
adds two buttons to a text box: One for increasing its value, one for decreasing
it. However the control also supports a web service call (or page method call).
Whenever the up or down button is clicked, the JavaScript code connects to the web
server and executes a method there. The method signature is the following one:
Function MethodName(ByVal current As Integer, ByVal tag As String) As Integer
The current argument is the current value in the text box; the tag attribute is
additional context data that can be set as a property of the NumericUpDown extender
(but is not required).
For this sample, the numeric up/down control shall only allow values that are powers of two: 1, 2, 4, 8, 16, 32, 64, and so on. Therefore, the method executed when the user wants to increase the value must double the old value; the other method must divide value by two. So here is the complete web service:
<%@ WebService Language="VB" Class="NumericUpDown1" %>
Imports System.Web
Imports System.Web.Services
Imports System.Web.Services.Protocols
<System.Web.Script.Services.ScriptService()> _
Public Class NumericUpDown1
Inherits System.Web.Services.WebService
<WebMethod()> _
Function Up(ByVal current As Integer, ByVal tag As String) As Integer
If current <= 536870912 Then
Return current * 2
Else
Return current
End If
End Function
<WebMethod()> _
Function Down(ByVal current As Integer, ByVal tag As String) As Integer
If current >= 2 Then
Return CInt(current / 2)
Else
Return current
End If
End Function
End Class
Finally, create a new ASP.NET page. As usual, you need a ScriptManager control,
a TextBox control and a NumericUpDownExtender control. For the latter, you have
to provide the web service information:
ServiceDownMethodname of the down web method or page methodServiceDownPathpath to the web service with the down service method; omit if you are using a page methodServiceUpMethodname of the up web method or page methodServiceUpPathpath to the web service with the up service method; omit if you are using a page method
Here is the complete markup for the page:
<%@ Page Language="VB" %>
<!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 id="Head1" runat="server">
<title>Control Toolkit</title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="asm" runat="server" />
<div>
How many MB do you want? <asp:TextBox ID="TextBox1" Text="32" runat="server" />
<ajaxToolkit:NumericUpDownExtender ID="nud" runat="server"
TargetControlID="TextBox1" Width="100"
ServiceUpPath="NumericUpDown1.vb.asmx" ServiceDownPath="NumericUpDown1.vb.asmx"
ServiceUpMethod="Up" ServiceDownMethod="Down" />
</div>
</form>
</body>
</html>
If you run the page, notice how the value in the text box always doubles when you click on the upper button, and is halved when you click on the lower button.
Only numbers that are a power of 2 appear (Click to view full-size image)
By Christian Wenz, Christian Wenz is an author, trainer, and consultant. His main focus of working and writing is on web technologies and security. Christian has written or co-written over 100 books for various publishers. He works with both open source and closed source web technologies. This leads to the unusual situation that he has both been awarded a Microsoft MVP for ASP/ASP.NET and is listed in Zend's Who is Who of PHP. He is also listed in Mozilla's credits (about:credits) and is considered an expert in browser-agnostic JavaScript.
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