Selecting or DeSelecting multiple checkbox inside a gridview

function SelectAllOrDeselect(CheckBox, Type, Column, HCheckBox) {
    try {
        var TotalChkBx = parseInt('<%= grd_EmpSelection.Rows.Count %>');
        var TargetBaseControl = document.getElementById('<%= grd_EmpSelection.ClientID%>');
        var TargetChildControl = null;

        if (Column == "1") TargetChildControl = "chkTestSelect";
        else TargetChildControl = "chkTrainingSelect";

        var Inputs = TargetBaseControl.getElementsByTagName("input");
        var SelectCount = 0;
        //Checked/Unchecked all the checkBoxes in side the GridView.
        if (Type == "1") {
            for (var iCount = 0; iCount < Inputs.length; ++iCount) {
                if (Inputs[iCount].type == 'checkbox' && Inputs[iCount].id.indexOf(TargetChildControl, 0) >= 0) 
                    Inputs[iCount].checked = CheckBox.checked;
            }

            //Reset Counter
            SelectCount = CheckBox.checked ? TotalChkBx : 0;
        } else if (Type == "2") {
            //Reset Counter
            for (var iCount = 0; iCount < Inputs.length; ++iCount) {
                if (Inputs[iCount].type == 'checkbox' && Inputs[iCount].id.indexOf(TargetChildControl, 0) >= 0) 
                    if (Inputs[iCount].checked == true) SelectCount++;
            }

            //Modifiy Counter;        
            if (!CheckBox.checked && SelectCount > 0) SelectCount--;

            //Change state of the header CheckBox.
            if (SelectCount < TotalChkBx) HCheckBox.checked = false;
            else if (SelectCount == TotalChkBx) HCheckBox.checked = true;
        }
    } catch (err) {}
}

protected void grd_EmpSelection_RowCreated(object sender, GridViewRowEventArgs e)
    {
        //e.Row.RowState == DataControlRowState.Edit not works on Alternating Rows 
        //if ((e.Row.RowState & DataControlRowState.Edit) > 0)
        if (e.Row.RowType == DataControlRowType.DataRow && (e.Row.RowState == DataControlRowState.Normal || e.Row.RowState == DataControlRowState.Alternate))
        {

            CheckBox chkTestSelectAll = (CheckBox)this.grd_EmpSelection.HeaderRow.FindControl("chkTestSelectAll");
            CheckBox chkTestSelect = (CheckBox)e.Row.Cells[1].FindControl("chkTestSelect");

            chkTestSelectAll.Attributes["onclick"] = string.Format("javascript:SelectAllOrDeselect(this,'1','1', {0});", chkTestSelectAll.ClientID);
            chkTestSelect.Attributes["onclick"] = string.Format("javascript:SelectAllOrDeselect(this,'2','1', {0});", chkTestSelectAll.ClientID);


            CheckBox chkTrainingSelectAll = (CheckBox)this.grd_EmpSelection.HeaderRow.FindControl("chkTrainingSelectAll");
            CheckBox chkTrainingSelect = (CheckBox)e.Row.Cells[1].FindControl("chkTrainingSelect");

            chkTrainingSelectAll.Attributes["onclick"] = string.Format("javascript:SelectAllOrDeselect(this,'1','2', {0});", chkTrainingSelectAll.ClientID);
            chkTrainingSelect.Attributes["onclick"] = string.Format("javascript:SelectAllOrDeselect(this,'2','2', {0});", chkTrainingSelectAll.ClientID);

        }
    }

The gridview checkbox will maintain the checked state during postback.

Reference
http://www.codeproject.com/KB/webforms/SelectingAllCheckBoxes.aspx