Asp.net - DataTable row indexes do no match the order when bound to Gridview

Barnabeck
September 1, 2023
112 views
0 votes
2 Answers

I have a Gridview with different items, ordered by the integer column "Order". I am saving the DataTable that feeds the Gridview as "Session Parameter".

Item        Order      LinkButtons
----------------------------------
Item1         1         up   down
Item2         2         up   down
Item3         3         up   down

The idea is to customize the order of the items by moving them up and down with the LinkButtons.

This is what I do:

I get the row index from the RowClick Event

LinkButton lb = (sender as LinkButton);
string OrderNr = lb.CommandArgument;
int OrderNummer = Convert.ToInt16(OrderNr);
GridViewRow row = (GridViewRow)lb.NamingContainer;
int idx = row.RowIndex;

Call the Session table and change the Order Parameter

DataTable t = Session["SessionData"] as DataTable;
t.Rows[idx][1] = Convert.ToString(OrderNummer - 1);
t.Rows[idx-1][1] = Convert.ToString(OrderNummer);

I then reorder the DataTable and bind it back to the Grid

t.DefaultView.Sort = "OderNr";
t = t.DefaultView.ToTable();

This unfortunately works only on the first Operation. Afterwards what is returned from t.Rows[idx] is unpredictable to me as the Gridrow Row Index doesn’t match the DataTable Row index.

Very confusing

Tags: asp.net c#session-variables

Answers

Not influent in C#, code may need optimization/fine-tuning.

aspx

<asp:GridView ID="GridView1" runat="server">
    <Columns>
        <asp:TemplateField ShowHeader="false">
            <ItemTemplate>
                <asp:LinkButton ID="Btn_UP" runat="server" Text="UP" CommandArgument='<%# Eval("Order") %>' OnCommand="Btn_UP_Command"></asp:LinkButton>
                <asp:LinkButton ID="Btn_DN" runat="server" Text="Down" CommandArgument='<%# Eval("Order") %>' OnCommand="Btn_DN_Command"></asp:LinkButton>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Page_Load

if (!IsPostBack)
{
    GridView1.DataSource = Get_DataTable();
    GridView1.DataBind();
}

Get_DataTable

public DataTable Get_DataTable()
{
    if (Session["dt"] == null)
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Item", typeof(string));
        dt.Columns.Add("Order", typeof(int));
        for (int i = 1; i <= 10; i++)
            dt.Rows.Add($"Item {i}", i);
        return dt;
    }
    else
        return (DataTable)Session["dt"];
}

Btn_UP_Command

DataTable dt = Get_DataTable();
int order = int.Parse(e.CommandArgument.ToString());
if (order == 1)
    return;
dt.Select($"Order={order}")[0]["Order"] = -1;
dt.Select($"Order={order - 1}")[0]["Order"] = order;
dt.Select("Order=-1")[0]["Order"] = order - 1;
dt.DefaultView.Sort = "Order";
Session["dt"] = dt.DefaultView.ToTable();
GridView1.DataSource = dt;
GridView1.DataBind();

Btn_DN_Command

DataTable dt = Get_DataTable();
int order = int.Parse(e.CommandArgument.ToString());
if (order == dt.Rows.Count)
    return;
dt.Select($"Order={order}")[0]["Order"] = -1;
dt.Select($"Order={order + 1}")[0]["Order"] = order;
dt.Select("Order=-1")[0]["Order"] = order + 1;
dt.DefaultView.Sort = "Order";
Session["dt"] = dt.DefaultView.ToTable();
GridView1.DataSource = dt;
GridView1.DataBind();

The problem here is that you using "default" view for the grid binding.

But default view DOES NOT change the row index of the base table!!!

This results in 2 possible solutions:

You consider using dataitem index from the GridView, and NOT row index.

Or, simpler is to sort the base table.

You can do this with this:

        rstData.DefaultView.Sort = "MyOrder";
        rstData = rstData.DefaultView.ToTable();
        Session["rstData"] = rstData;

Note VERY close in above, we have to shove the rstData table BACK into session[], since we have re-built the table with .ToTable(), and that in effect is a new instance of the object.

So, here is a working example (I have included the MyOrder column in this example). Also keep in mind, that rows are 0 based, and your example started with 1. For this example, "MyOrder" column starts at 0, and not one.

So, say this markup:

<asp:GridView ID="GVHotels" runat="server" AutoGenerateColumns="False"
    DataKeyNames="ID" CssClass="table" 
    Width="45%" >
    <Columns>
        <asp:BoundField DataField="FirstName" HeaderText="FirstName" />
        <asp:BoundField DataField="LastName" HeaderText="LastName" />
        <asp:BoundField DataField="City" HeaderText="City" />
        <asp:BoundField DataField="HotelName" HeaderText="HotelName" />
        <asp:BoundField DataField="Description" HeaderText="Description" />
        <asp:BoundField DataField="MyOrder" HeaderText="Order" />
        <asp:TemplateField>
            <ItemTemplate>
                <asp:Button ID="cmdUp" runat="server" Text="UP"
                    OnClick="cmdUp_Click" CssClass="btn" />
            </ItemTemplate>
        </asp:TemplateField>

        <asp:TemplateField>
            <ItemTemplate>
                <asp:Button ID="cmdDown" runat="server" Text="Down"
                    OnClick="cmdDown_Click" CssClass="btn" />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

And code behind:

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string strSQL = @"SELECT * FROM tblHotelsA
                        WHERE Active = 1";

            rstData = General.MyRst(strSQL);
            LoadGrid();
        }
        else
            rstData = (DataTable)Session["rstData"];
    }

    void LoadGrid()
    {
        rstData.DefaultView.Sort = "MyOrder";
        rstData = rstData.DefaultView.ToTable();
        Session["rstData"] = rstData;
        GVHotels.DataSource = rstData;
        GVHotels.DataBind();

    }

    protected void cmdUp_Click(object sender, EventArgs e)
    {
        Button btn = (Button)sender;
        GridViewRow gRow = (GridViewRow)btn.NamingContainer;
        int IX = gRow.RowIndex;            
        if (IX > 0)
        {
            rstData.Rows[IX]["MyOrder"] = IX - 1;
            rstData.Rows[IX - 1]["MyOrder"] = IX;
            LoadGrid();
        }
    }

    protected void cmdDown_Click(object sender, EventArgs e)
    {
        Button btn = (Button)sender;
        GridViewRow gRow = (GridViewRow)btn.NamingContainer;
        int IX = gRow.RowIndex;
        if (IX < rstData.Rows.Count - 1)
        {
            rstData.Rows[IX]["MyOrder"] = IX + 1;
            rstData.Rows[IX + 1]["MyOrder"] = IX;
            LoadGrid();
        }
    }

The result is this:

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Asp.net – DataTable row indexes do no match the order when bound to Gridview

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