Visualforce - Beyond Basics Series 18 - Use Variables in Page

How to use variables in page ?

Visualforce page/component can use,

•   global variables
•   Functions
•   parameters from controller/extensions
•   local variables

I haven't seen many developers using variables that often. It's created using variable tag. It could be used when you have a very lengthy variable names (or) complex Function output (or) lengthy relationship chain to access parameters in controller/extension.

What is the advantage of it ?

It has all the advantages that a variable has in a programming language.

•    A common place to access it's value
•    No need to change it in all the place, if we ever want to change it
•    We can give a meaningful variable name
•    Code looks clean
•    Improve maintainablity

How to use them dynamically ?

We could either assign the variable name statically like this,
<apex:variable value="{!$CurrentPage.Name}" var="current_page_name"/>
or dynamically like this which means the varname could be any value dynamically assigned from anywhere.
<apex:variable value="{!$CurrentPage.Name}" var="{!varname}"/>

Where is the code ?

This is the illustration of showing static variable assignment. 'TodaysDate' is a controller parameter. But, you can dynamically, changes its value in the component using  variable assignment. you can see that in the code below,

	public class testcls5_12122016 {
	public Date TodaysDate { get; set;}
	public testcls5_12122016() {
	TodaysDate = System.Today();
	}
	}

view raw gistfile1.txt hosted with ❤ by GitHub

	<apex:component >
	<apex:attribute type="string" name="var" description="variable name"/>
	<!-- Dynamic variable Name -->
	<apex:variable var="{!var}" value="This is dummy value"/>
	<apex:componentBody/>
	</apex:component>

view raw gistfile1.txt hosted with ❤ by GitHub

	<apex:page controller="testcls5_12122016">
	<!-- Static variable Name -->
	<apex:variable var="currentpage" value="{!$CurrentPage.Name}"/>
	<!-- Output to User -->
	Current page is - {!currentpage}
	<!-- Dynamic variable Name -->
	<c:testcmp5_12122016 var="TodaysDate">
	Today's Date is {!TodaysDate}
	</c:testcmp5_12122016>
	</apex:page>

view raw gistfile1.txt hosted with ❤ by GitHub