In this article I will demonstrate how to create treeview in visualforce page.
Here in Visualforce Page displays a collapsible treeview, with Accounts and Contacts related to the account.
For this development we need JQuery plugins. Download the Jquery Plugin from here and Upload this Zip file into Static Resources with the name “JqueryTreeView”.

Create Apex class with following code:

public with sharing class TestTreeView
{
    //Wrapper class to contain the parent nodes and their child nodes
    public class WCTreeView
    {    
        public List<contact> Child {get; set;}
        Public Account Parent {get;set;}
         
        public WCTreeView(Account objAC, List<contact> objCList)
        {
            Child = objCList;
            Parent = objAC;
        }
    }
 
    Public List<wctreeview> TreeView;
     
    Public List<wctreeview> GetNodes()
    {
        TreeView = new List<wctreeview>();
        List<account> objACList = [Select Id, Name from Account];
        for (Integer i = 0; i < objACList.size(); i++)
        {
            List<contact> objCList = [Select Id, FirstName, LastName from Contact where AccountId = :objACList[i].Id];
            TreeView.add(new WCTreeView(objACList[i], objCList));
        }   
        return TreeView;
    }   
}

Now create the Visualforce page:

<apex:page controller="TestTreeView">
<!-- Include the Jquery Script files -->
<link href="{!URLFOR($Resource.JqueryTreeView,'Jquerytreeview/jquery.treeview.css')}" rel="stylesheet">
<script src="{!URLFOR($Resource.JqueryTreeView,'Jquerytreeview/jquery.js')}" type="text/javascript"></script>
<script src="{!URLFOR($Resource.JqueryTreeView,'Jquerytreeview/jquery.cookie.js')}" type="text/javascript"></script>
<script src="{!URLFOR($Resource.JqueryTreeView,'Jquerytreeview/jquery.treeview.js')}" type="text/javascript"></script>
<!-- End of Javascript files -->
<script type="text/javascript">
$(function() {
 $("#idTreeView").treeview({
 collapsed: true,
 animated: "medium",
 control:"#IdTreeControl",
 persist: "location"
 });
})
</script>
<!-- Start TreeView -->


<div id="IdTreeControl">
<a href="https://www.blogger.com/blogger.g?#"><span style="color: black;">Collapse All</span></a> | 
<a href="https://www.blogger.com/blogger.g?#"><span style="color: black;">Expand All</span></a>
</div>




<ul id="idTreeView">
<apex:repeat value="{!Nodes}" var="Pitem">


<li>
<b><apex:outputtext escape="false" style="color: black;" value="{!Pitem.Parent.Name}"></apex:outputtext></b>


<ul>
<apex:repeat value="{!Pitem.Child}" var="Citem">


<li>
<span class="formattextcon"><apex:outputtext escape="false" style="color: red;" value="{!Citem.LastName}"></apex:outputtext></span>
</li>


</apex:repeat>  
</ul>


</li>


</apex:repeat>
</ul>


<!-- End of TreeView -->      
</apex:page>

And here is the output:

Action support component adds AJAX support to other component. It allow the component to be refreshed asynchronously by calling the controller’s method when any event occurs (like onclik, onblur etc). It also allows to rerender page sections as desired.
In this article I will demonstrate how to use actionsupport in visualforce page.
Create Apex class with following code:

Public with sharing class TestActionSupport
{
    public Integer Total {get;set;}
     
    Public TestActionSupport()
    {
        Total = 0;
    }
     
    Public void IncreaseNumber()
    {
        Total ++;
    }
}

Now create the Visualforce page:

<apex:page controller="TestActionSupport">
<apex:form>
<apex:pageblock>
<apex:pageblocksection>
<apex:outputpanel id="idPanel1"> 
<apex:outputtext value="Click here to increase number">
<apex:actionsupport action="{!IncreaseNumber}" event="onclick" rerender="idResult">
</apex:actionsupport></apex:outputtext></apex:outputpanel>
<apex:outputtext id="idResult" label="No. of Clicked:" value="{!Total}">
</apex:outputtext></apex:pageblocksection>
</apex:pageblock>
</apex:form>
</apex:page>

In the above apex class, initially variable “Total” value is set to 0. But when we will click on visualforce page “Click here to increase number” then controller action method will be called and variable “Total” will be increase. The action support also rerender the outputText which refreshes the outputText and hence shows the new value set in controller method.

Before Click:

After Click: