[转载]固定(冻结)表头及首列DataGrid

来源：codeproject 作者：David R Lewis

Introduction
During a recent project, I was asked to make the DataGrid behave like an Excel

freeze pane. That’s right; freeze the header row and freeze the left column of

a DataGrid. After several hours of searching for someone that has done this and

posted the code, I gave up and tried to figure out a solution myself. The

project source code above provides three ASPX files. One to lock the column(s) from the client side, one to lock the column (s) from

the server side, and one to lock the column from the server side and then

unlock/lock the column from the client side.

Background
The plan is actually fairly simple. While browsing the net for a solution, I

found a great article on how to create a freeze pane from an HTML table. The

solution is CSS based and only works with Internet Explorer, but does degrade

well in other browsers. I would like to thank Brett Merkey for providing this

solution. His ‘Lock or Freeze Columns with Non-scroll headers’ provided me

with the idea and can be viewed here.

The solution is fairly simple, and in the end, you will have two different

ways to lock the DataGrid columns.

Here is a synopsis of what we will be doing to create the freeze pane effect:

Creating a simple DataGrid with data surrounded by a <div> tag.
Modifying the DataGrid to render <th> tags inside the header row.
Creating a style sheet that will lock the DataGrid header row and column(s).
Locking the column(s) from the client side.
Locking the column(s) for the server side.
Using the code
Modifying the DataGrid to render <th> tags
The first problem that we run into is that the DataGrid does not render

the <th> element but rather the common <td> element in the header. Luckily for us,

Microsoft put out a rather obscure hotfix for this. Most of us have already

downloaded this hotfix without knowing it. You can view more information (or

download it if you have not done so yet) here.

Among other things, this hotfix adds the property UseAccessibleHeader to the

DataGrid. This property, when set to true, ‘renders DataGrid table headers in

<th> tags with a scope="col" attribute.’

The finished DataGrid code will look something like this:

Creating the style sheet
The style sheet is the key to this project. There are two things that need

to be noted. First, CSS expressions are used. CSS expressions were

introduced in Internet Explorer 5.0, and it allows you to assign a JavaScript

expression to a CSS property. In this case, we are setting the horizontal

and vertical scrolling position of the document elements by using expressions.

Second, there is a certain order in which the styles need to be set. If you

change the order of the styles listed below, you will come up with some rather

odd results. And in case you’re wondering… yes I went through almost every

incorrect order before actually coming up with an order that works.
Here is the CSS code:

/* Div container to wrap the datagrid */
div#div-datagrid {
width: 420px;
height: 200px;
overflow: auto;
scrollbar-base-color:#ffeaff;
}

/* Locks the left column */
td.locked, th.locked {
font-size: 14px;
font-weight: bold;
text-align: center;
background-color: navy;
color: white;
border-right: 1px solid silver;
position:relative;
cursor: default;
/*IE5+ only*/
left: expression(document.getElementById("div-datagrid").scrollLeft-2);
}

/* Locks table header */
th {
font-size: 14px;
font-weight: bold;
text-align: center;
background-color: navy;
color: white;
border-right: 1px solid silver;
position:relative;
cursor: default;
/*IE5+ only*/
top: expression(document.getElementById("div-datagrid").scrollTop-2);
z-index: 10;
}

/* Keeps the header as the top most item. Important for top left item*/
th.locked {z-index: 99;}

/* DataGrid Item and AlternatingItem Style*/
.GridRow {font-size: 10pt; color: black; font-family: Arial;
             background-color:#ffffff; height:35px;}
.GridAltRow {font-size: 10pt; color: black; font-family: Arial;
             background-color:#eeeeee; height:35px;}

Locking the column(s) from the client side
In order to lock the column from the client side, we just need to create a

script that changes the style of the first column to ‘locked’. Multiple

columns can be frozen just by modifying the code below. The following

script is added to the head of the ASPX file to lock the first column.

Locking the column(s) from the server side
Again, in order to lock the column from the server side, we just need

to change the style of the first column to ‘locked’. In order to

implement this, we use the ItemDataBound method of the DataGrid.

The following code sets the style of the first column to ‘locked’.

This is actually extremely simple with the code below:

Sub Item_Bound(ByVal sender As Object, ByVal e As DataGridItemEventArgs) _
Handles DataGrid1.ItemDataBound
e.Item.Cells(0).CssClass = "locked"
End Sub

And to freeze the first two columns, it’s just as easy: