Table with Fixed Header

Sometimes we need to display an html table with fixed header,following is the code for a table with fixed header.

This task can be completed with keeping two things in mind.

 1. Div tag with style="height:300px; overflow:auto;”
  This makes division section fixed in page and allow scrollbar to apper.

 2. Making Table header position relative to parent (div) ,
  <tr style="position:relative; top:expression(offsetParent.scrollTop); ">
  
 In this example, I have added 2 elements in table, to see the effect you need to enter more elements that exceeds the div tag height.

 Moreover, we can use style="position:relative; top:expression(offsetParent.scrollTop); " to make header fixed for datagrid also.


 CODE:
<div style="height:300px; overflow:auto; ">
  <table cellspacing="5" width= "952px" style="border-right: black thin solid; border-top: black thin solid; border-left: black thin solid; border-bottom: black thin solid; border-collapse: separate; table-layout: auto; vertical-align: middle; overflow: auto; text-align: center; background-color: navajowhite;" cellpadding="5" frame="box">
  <thead style="background:Brown">
  <tr style="position:relative; top:expression(offsetParent.scrollTop);">
  <th>Station</th>
  <th>Date</th>
  <th>Status</th>
  <th style="width: 161px">Num.</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>KABC</td>
  <td>09/12/2002</td>
  <td>Submitted</td>
  <td>0</td>
  </tr>
  <tr>
  <td>KCBS</td>
  <td>Lockdown</td>
  <td></td>
  <td>2</td>
  </tr> 
  </tbody>
  </table>
</div >

Nullable type in .Net 2.0

Nullable type allows a varible to store null value, Infact this is the special about the type. The main purpose is it will add two members to the variable HasValue and Value Members.
for example, if you store data for a yes/no question and if the user did not answer the question then null will be stored in that place. This means it stores True, False and third state nothing as null also. This will be represented as shown below.

In VB.Net,
Dim b as Nullable(Of Boolean) = Nothing
.....
If b.HasValue Then
Do if b has some value and not null
Else
Do if b is null
End If
In C#,
Nullable b = null;

Otherwise it can be used this way also, only applicable for C#,
bool? b = null;
.....
if (b.HasValue) {Do if it is not null} else {Do if it null}