Question

Basically I want to implement a filtering option for a Grid view and I have a dropdown list containing the column names and a checkboxlist containing the available filtering values for that column. Every time I select a different column, I have to load the filtering values for that column into the checkbox list.
The problem I have is that when I change the column in the dropdown list, the event for the checklist is fired and the application crashes.

My controls are defined like this:

<div class="LeftAligned">  
     <asp:Label ID="FilterLabel" runat="server" Text="Filter by:" />  
     <asp:DropDownList runat="server" ID="FilterReviewsDropDownList" AutoPostBack="true" OnSelectedIndexChanged="FilterReviewsDropDownList_SelectedIndexChanged" />  
     <asp:ImageButton ID="FilterReviewsButton" runat="server" ImageUrl="~/images/filter.png" AlternateText="VALUE" CssClass="filter_button" OnClick="FilterReviewsButton_Click" />  
     <div onmouseout="javascript:bMouseOver=false;" onmouseover="javascript:bMouseOver=true;" class="filter_div">  
           <asp:CheckBoxList AutoPostBack="true" ID="FilterReviewsCheckBoxList" ClientIDMode="Static" runat="server" CssClass="filter_checklist collapsed"   
            OnSelectedIndexChanged="FilterReviewsCheckBoxList_Selected">  
           </asp:CheckBoxList>  
     </div>  
     <%--asp:Button runat="server" ID="ApplyFilterButton" Text="Apply Filter" OnClick="ApplyFilterButton_Click"/>  
     <asp:Button runat="server" ID="ClearFilterButton" Text="Clear Filter" OnClick="ClearFilterButton_Click"/--%>  
</div>

In the CodeBehind file I have the following code:

protected void FilterReviewsButton_Click(object sender, EventArgs e)
{
    FilterReviewsCheckBoxList.CssClass = "filter_checklist";
}

protected void FilterReviewsDropDownList_SelectedIndexChanged(object sender, EventArgs e)
{
    LoadFilterCheckboxes(FilterReviewsDropDownList.SelectedIndex);
}

private void LoadFilterCheckboxes(int iColumn)
{
    SortedSet<string> oItems = new SortedSet<string>();

    for (int i = 0; i < ReviewsGridView.Rows.Count; i++)
    {
        IEnumerable<Label> oLabels = ReviewsGridView.Rows[i].Cells[iColumn].Controls.OfType<Label>();
        string sValue = "";
        if (oLabels != null && oLabels.Count() > 0)
        {
            sValue = oLabels.First().Text;
        }
        else
        {
            sValue = ReviewsGridView.Rows[i].Cells[iColumn].Text;
        }
        if (!oItems.Contains(sValue))
            oItems.Add(sValue);
    }

    FilterReviewsCheckBoxList.Items.Clear();
    FilterReviewsCheckBoxList.Items.Add("All");
    FilterReviewsCheckBoxList.Items[0].Selected = true;
    foreach (string sItem in oItems)
    {
        FilterReviewsCheckBoxList.Items.Add(sItem);
        FilterReviewsCheckBoxList.Items[FilterReviewsCheckBoxList.Items.Count - 1].Selected = true;
    }
}

protected void FilterReviewsCheckBoxList_Selected(object sender, EventArgs e)
{
    string sResult = Request.Form["__EVENTTARGET"];
    if (string.IsNullOrEmpty(sResult))
    {
        FilterReviewsCheckBoxList.Items[0].Selected = true; //weird bug fix...
        return;
    }

    string[] sCheckedBox = sResult.Split('$');
    //get the index of the item that was checked/unchecked
     int i = int.Parse(sCheckedBox[sCheckedBox.Length - 1].Split('_')[1]);
     if (i == 0)
     {
         if (FilterReviewsCheckBoxList.Items[i].Selected == true)
         {
             for (int j = 1; j < FilterReviewsCheckBoxList.Items.Count; j++)
                 FilterReviewsCheckBoxList.Items[j].Selected = true;
         }
         else
         {
            for (int j = 1; j < FilterReviewsCheckBoxList.Items.Count; j++)
                FilterReviewsCheckBoxList.Items[j].Selected = false;
         }
     }
     else
     {
        if (FilterReviewsCheckBoxList.Items[i].Selected == false)
        {
            FilterReviewsCheckBoxList.Items[0].Selected = false;
        }
        else
        {
            //if (oFirstTable != null)
            //{
            //    oTable = oFirstTable;
            //    oView = oTable.DefaultView;
            //}
            bool bAllChecked = true;
            for (int j = 1; j < FilterReviewsCheckBoxList.Items.Count; j++)
            {
                 if (FilterReviewsCheckBoxList.Items[j].Selected == false)
                 {
                     bAllChecked = false;
                     break;
                 }
            }
            if (bAllChecked)
                 FilterReviewsCheckBoxList.Items[0].Selected = true;
        }
    }
}

Any idea of why FilterReviewsCheckBoxList_Selected is called (with the dropdownlist as the sender argument) when changing the dropdown list?

Answer 1

For anyone who may encounter the same problem, the fix is to avoid static binding of the grid view to entity data source. Instead, bind the grid dynamically in the page load event.