condional rendering with a redirect - salesforce

Question

Here is the set up. I have a standard page layout with custom buttons.
When the user clicks a button, i want to check a value in the extension class. If the value is null or 0- i want a pages message to appear, otherwise i want to redirect them to another VF page.
the way that i'm attempting to do this is put a VF section on the page layout, and have it conditionally rendered using an action:support method, but I can't get it to work..
HALP!

Answer 1

You do not need to add a VF page to the layout.
Try to use the Salesforce AJAX Toolkit for your custom button:
1) First create a WebService to calculate your value:
global with sharing class yourController{
WebService static Integer calculateValue(Integer i) {
Integer result = i + 5;
return result;
}
}
2) Then create a custom button for your object: Display Type -
Detail Page Button Behavior - Execute JavaScript Content Source - onClick JavaScript
3) Then add this code to the button:
// Loading the ajax toolkit data
{!REQUIRESCRIPT("/soap/ajax/20.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/10.0/apex.js")}
// Making a call to the webservice method
var value = sforce.apex.execute("yourController","calculateValue", {i:5});
// If the value is 0 or blank
if(value == 0 || value == ''){
// Pop up a message
alert('Your message text here');
else{
// Otherwise redirecting user to another page
window.location = "/apex/YourCustomPage";
}
4) Now save your button and do not forget to add it to the layout page :)

Answer 2

If the method called from the button returns a PageReference, you can create a PageReference object and use the .setRedirect( True) method to do a redirect. You're probably returning Null right now, which indicates "no action".
You can set the target of the redirect when you create the PageReference, or use the new ApexPages.StandardController() method to select one of the controllers for a given object type, or just Page.vfPageName to reference another Visualforce page.
When your method returns that PageReference, the browser will redirect to the new URL.