call a vb.net subrouting from a javascript function? - asp.net

Question

hi folks i have a subroutine called CheckDate() in the code behind.
How would I call that subroutine from a javascript function?
Cheers,
-Jonesy

Answer 1

You can't call it directly as function call.
because Javascript is a scripting langauge aimed for web browsers.
you may use AJAX or full page post sending the parameters to allow you to execute the subroutine.
Read more about Ajax it is the better way to go.

Answer 2

To expand on what Kronass said there I've found this article to be useful in the past for doing what you want http://encosia.com/2008/05/29/using-jquery-to-directly-call-aspnet-ajax-page-methods/. Encosia also has a heap of other blog plots on this if you do a bit of searching
What you're looking to use is normally called a WebMethod, ScriptMethod or Page Method depending on which framework you're using

Answer 3

One way to do this is by using the ICallbackEventHandler interface. I saw you had a question regarding the AjaxControToolkit CalendarExtender the other day so I'm guessing this question is in relation to that and how you do some validation in a server-side method. ICallbackEventHandler is AJAX, but you can write your validation as a normal method, not a PageMethod/WebMethod. It's slightly more fiddly on the Javascript side, but not by much.
Let's start with our basic textbox and calendar extender:
<form id="form1" runat="server">
<asp:ScriptManager runat="server" ID="ScriptManager" />
<div>
<asp:TextBox runat="server" ID="DateTextBox" />
<ajaxtoolkit:CalendarExtender runat="server" ID="CalendarExtender" TargetControlID="DateTextBox"
PopupButtonID="SelectorButton" OnClientDateSelectionChanged="checkDate" Format="dd MMM yyyy" />
<asp:ImageButton runat="server" ID="SelectorButton" ImageUrl="Path to a pretty graphic" />
<br />
<asp:Label runat="server" ID="ValidDateLabel" />
</div>
</form>
I've added the OnDateSelectionChanged attribute of the extender as this will kick off the process of calling the server-side method; we'll come back to what goes in there shortly.
In the class declaration in your code-behind, you need to say that you are implementing the interface:
Partial Public Class _Default
Inherits System.Web.UI.Page
Implements ICallbackEventHandler
To implement the interface we then need to add two more methods to handle the two methods in the interface, RaiseCallbackEvent and GetCallbackResult. We also need a property for a bit of temporary storage of the date we are trying to validate.
Private mCallbackDate As Date
Private Property CallbackDate() As Date
Get
Return mCallbackDate
End Get
Set(ByVal value As Date)
mCallbackDate = value
End Set
End Property
Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements ICallbackEventHandler.RaiseCallbackEvent
'eventArgument will contain the date the user selected from the extender
Dim testDate As Date
If eventArgument = String.Empty Then
Else
If Date.TryParse(eventArgument, testDate) Then
'If we have a legal date selected then store it
Me.CallbackDate = testDate
End If
End If
End Sub
Public Function GetCallbackResult() As String Implements ICallbackEventHandler.GetCallbackResult
Dim result As String = String.Empty
'Get the date that we stored in memory and pass it to our CheckDate function
'We'll pass back to the Javascript in the page the string 'true' if the date is
'valid under our business rules and 'false' if it isn't
If checkDate(Me.CallbackDate) Then
Return "true"
Else
Return "false"
End If
End Function
Public Function checkDate(ByVal dateToCheck As Date) As Boolean
'If the date is in the future then return True, otherwise False
If dateToCheck > Date.Today Then
Return True
Else
Return False
End If
End Function
There's one more bit of server-side we need to add, in Page_Load, which does the hooking up of the Javascript and server-side code. The ClientScriptManager's GetCallbackEventReference function will inject a bit of script into our page that takes care of the communication between browser and server. Then we just need to register a script block that calls the injected script - we'll call this function checkDateOnServer.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim callbackScript As String
callbackScript = "function checkDateOnServer(arg){" & _
Page.ClientScript.GetCallbackEventReference(Me, "arg", "receiveDateValidation", "") & _
"}"
ClientScript.RegisterClientScriptBlock(Me.GetType, "callback", callbackScript, True)
End Sub
Back to the client-side bits. We need to write a Javascript checkDate function that'll pass the user's selected date into the callback.
function checkDate()
{
// Get the date the user selected
var selectedDate = document.getElementById('DateTextBox').value;
// This will start the callback sequence
checkDateOnServer(selectedDate);
}
The last bit we need to do is receive the value coming back from the server, which we said in Page_Load would be called receiveDateValidation.
function receiveDateValidation(arg, context)
{
var ValidDateLabel = document.getElementById('SelectedDateLabel');
// We get a string value back from the server which is 'true' or 'false'
if (arg == 'true')
{
ValidDateLabel.innerText = 'Your date IS valid';
}
else
{
ValidDateLabel.innerText = 'Your date IS NOT valid';
}
}