Question

I am using this tutorial to freeze the header of the GridView. I did everything as explained in the tutorial but I got the following error in IE9 and I don’t know why.

Error:
Line: 182

Error: Unable to get value of the property ‘offsetWidth’: object is
null or undefined

I defined the GridView in the Javascript code as show below:

 <script type = "text/javascript">
    var GridId = "<%=GridView1 %>";
    var ScrollHeight = 300;
    window.onload = function () {
        var grid = document.getElementById(GridId);
        var gridWidth = grid.offsetWidth;
        var gridHeight = grid.offsetHeight;
        var headerCellWidths = new Array();
        for (var i = 0; i < grid.getElementsByTagName("TH").length; i++) {
            headerCellWidths[i] = grid.getElementsByTagName("TH")[i].offsetWidth;
        }
        grid.parentNode.appendChild(document.createElement("div"));
        var parentDiv = grid.parentNode;

        var table = document.createElement("table");
        for (i = 0; i < grid.attributes.length; i++) {
            if (grid.attributes[i].specified && grid.attributes[i].name != "id") {
                table.setAttribute(grid.attributes[i].name, grid.attributes[i].value);
            }
        }
        table.style.cssText = grid.style.cssText;
        table.style.width = gridWidth + "px";
        table.appendChild(document.createElement("tbody"));
        table.getElementsByTagName("tbody")[0].appendChild(grid.getElementsByTagName("TR")[0]);
        var cells = table.getElementsByTagName("TH");

        var gridRow = grid.getElementsByTagName("TR")[0];
        for (var i = 0; i < cells.length; i++) {
            var width;
            if (headerCellWidths[i] > gridRow.getElementsByTagName("TD")[i].offsetWidth) {
                width = headerCellWidths[i];
            }
            else {
                width = gridRow.getElementsByTagName("TD")[i].offsetWidth;
            }
            cells[i].style.width = parseInt(width - 3) + "px";
            gridRow.getElementsByTagName("TD")[i].style.width = parseInt(width - 3) + "px";
        }
        parentDiv.removeChild(grid);

        var dummyHeader = document.createElement("div");
        dummyHeader.appendChild(table);
        parentDiv.appendChild(dummyHeader);
        var scrollableDiv = document.createElement("div");
        if(parseInt(gridHeight) > ScrollHeight){
             gridWidth = parseInt(gridWidth) + 17;
        }
        scrollableDiv.style.cssText = "overflow:auto;height:" + ScrollHeight + "px;width:" + gridWidth + "px";
        scrollableDiv.appendChild(grid);
        parentDiv.appendChild(scrollableDiv);
    }
</script>

So how I fix this problem?

Answer 1

You have written code incorrectly

Instead of

var GridId = "<%=GridView1 %>";

Change to

var GridId = "<%=GridView1.ClientID %>"; //<= Check this

When ASP.Net controls are rendered their Id gets mangled and to get the mangled on client side the notation is as shown above.

Hope this solves your problem.