ASP.NET 2.0 AJAX Extensions Update Panel - Nested Update Panel

The thumb rule with nested update panels is as follows:-
Parent Update Panel refreshes all the contents including Child Update Panel's contents even if the Child Update Panel's update mode is set to Conditional; Child Update Panel refreshes only its contents and doesnt refresh that of the Parent Update Panel unless, the update mode for the parent update panel is not set to Conditional;The HTML for the Nested Update Panel is as below:-

<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<div>
<table width="80%" border="3">
<tr>
<td>
Label outside all the Update Panels
<asp:Label ID="Label3" runat="Server" Font-Bold="true"></asp:Label>
<br />
<br />
<asp:Button ID="Button3" runat="Server" Text="Refresh" />
<br />
<br />
</td>
</tr>
<tr>
<td>
<table width="65%" border="2">
<tr>
<td>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
Label within the Parent Update Panel
<asp:Label ID="Label1" runat="server" Font-Bold="true"></asp:Label>
<br />
<br />
<asp:Button ID="Button1" runat="server" Text="Refresh" />
<table width="40%" border="1">
<tr>
<td>
<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<br />
<br />
Label within the Child Update Panel
<asp:Label ID="Label2" runat="server" Font-Bold="True"></asp:Label>
<br />
<br />
<asp:Button ID="Button2" runat="server" Text="Refresh" />
</ContentTemplate>
</asp:UpdatePanel>
</td>
</tr>
</table>
</ContentTemplate>
</asp:UpdatePanel>
</td>
</tr>
</table>
</td>
</tr>
</table>
</div>
</form>

Code behind
protected void Page_Load(object sender, EventArgs e){
Label1.Text = System.DateTime.Now.ToString();
Label2.Text = System.DateTime.Now.ToString();
Label3.Text = System.DateTime.Now.ToString(); }
When you run the above page, you will notice that the label outside the Update Panels, the parent update panel contents and the child update panel contents.
When you click on the top most button, it refreshes the whole page and subsequently, all the labels get refreshed with the new date time.
However, when you click on the second refresh button which is marked inside the Parent Update Panel you will notice that the top most label doesnt get refreshed but both the Label 2 and Label 3 gets refreshed, although I have marked UpdateMode as conditional for the Child UpdatePanel. The reason being, the parent updates all the child update panels nested within.
Finally, when you click on the last Refresh button which is marked inside the Child Update Panel, you will notice that only the respective label gets refreshed.
Note that, if I remove the property UpdateMode=Conditional for the UpdatePanel1 (parent), both the labels will get refreshed.

ASP.NET 2.0 AJAX Extensions Update Panel - Multiple Update Panels

One of the main properties of an UpdatePanel is its UpdateMode property. The UpdateMode property is by default set to "Always".
However, when you have more than a single update panel or when you want to control as to when the Update Panel needs to get refresh, then setting the UpdateMode property to "Condition" is the first step.
Let us consider a scenario where we have 3 Update Panels in a page. The HTML for the same is as below:-
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<div>
<table width="100%">
<tr>
<td style="height: 64px">
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<b><u>Section 1</u></b>
<br /><br />
<asp:Label ID="Label1" runat="server"></asp:Label>
<asp:TextBox ID="TextBox1" runat="server" />
<br /><br />
<asp:Button ID="Button1" runat="Server" Text="Refresh" OnClick="Button1_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</td>
<td style="height: 64px">
<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<b><u>Section 2</u></b>
<br /><br />
<asp:Label ID="Label2" runat="server"></asp:Label>
<asp:TextBox ID="TextBox2" runat="server" />
<br /><br />
<asp:Button ID="Button2" runat="Server" Text="Refresh" OnClick="Button2_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</td>
<td style="height: 64px">
<asp:UpdatePanel ID="UpdatePanel3" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<b><u>Section 3</u></b>
<br /><br />
<asp:Label ID="Label3" runat="server"></asp:Label>
<asp:TextBox ID="TextBox3" runat="server" />
<br /><br />
<asp:Button ID="Button3" runat="Server" Text="Refresh" OnClick="Button3_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</td>
</tr>
</table>
</div>
</form>
Note that for all the UpdatePanels, I have set the UpdateMode to conditional. The application logic or codebehind for the above is as follows:-
protected void Page_Load(object sender, EventArgs e){
Label1.Text = System.DateTime.Now.ToString();
Label2.Text = System.DateTime.Now.ToString();
Label3.Text = System.DateTime.Now.ToString(); }
protected void Button1_Click(object sender, EventArgs e) { TextBox2.Text = TextBox1.Text; }
protected void Button2_Click(object sender, EventArgs e){ }
protected void Button3_Click(object sender, EventArgs e){ }
When you run this page, you will notice that there are four Sections - Section 1, 2 & 3. When you click on the Refresh button, the date time value gets refreshed only for the particular section. The other values doesnt get changed.
If you remove the UpdateMode=Conditional from the above UpdatePanel declarations, you will notice that all the labels get refreshed.
Hence, setting the UpdateMode as Conditional is important if you like to control the way the UpdatePanels get refreshed.

Singleton Pattern class vs. Static Classes

(1) Static Class cannot be extended whereas singleton pattern class can be extended.
(2) Static Class can still have instances (unwanted instances) whereas singleton pattern class prevents it.
(3) Static Class cannot be initialized with a STATE(parameter), whereas singleton pattern class can.
Note: The difference is in Singleton pattern there is an instance of an object and the object resides in Heap memory area and can be passed in different threads.
But if u make the entire class as static with all static methods there will be no object instance, your entire code will be just loaded in the code section.