Why is textbox.Text returning an empty string?

Question

First let me preface this with the fact that I know this question has been asked a slew of times. I've tried implementing everything I've read and have not resolved my issue yet.

I have a shopping cart being displayed in a GridView and I am trying to get the update function to work. After I click edit (on the row in question) and I change the value in the textbox, and then click update, I am always getting an empty string returned.

I've read countless posts about it being a PostBack issue, however I have encapsulated my DataBind method within an if(!Page.IsPostBack){} so I dont believe that is my issue.

These are the relevant methods in my CodeFile:

protected void Page_Load(object sender, EventArgs e)
{

    if (Session["thisCart"] == null)
    {
        Session["thisCart"] = new ShoppingCart();
    }
    thisCart = (ShoppingCart)Session["thisCart"];

    if (!Page.IsPostBack)
    {
        FillData();
    }

}

private void FillData()
{
    gvShoppingCart.DataSource = thisCart.Items;
    gvShoppingCart.DataBind();
    if (thisCart.Items.Count == 0)
    {
        lblGrandTotal.Visible = false;
    }
    else
    {
        lblGrandTotal.Text = string.Format("Grand Total = {0,19:C}", thisCart.GrandTotal);
        lblGrandTotal.Visible = true;
    }
}

protected void gvShoppingCart_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
    TextBox txtQuantity = (TextBox)gvShoppingCart.Rows[e.RowIndex].Cells[3].Controls[0];
    int quantity = Int32.Parse(txtQuantity.Text);
    thisCart.Update(e.RowIndex, quantity);
    gvShoppingCart.EditIndex = -1;
    FillData();        
}

And this is the aspx file:

<asp:GridView ID="gvShoppingCart" runat="server" AutoGenerateColumns="False" OnRowCancelingEdit="gvShoppingCart_RowCancelingEdit" OnRowDeleting="gvShoppingCart_RowDeleting" OnRowEditing="gvShoppingCart_RowEditing" OnRowUpdating="gvShoppingCart_RowUpdating" ClientIDMode="AutoID">
    <Columns>
        <asp:BoundField DataField="NAME" HeaderText="Product name" ReadOnly="True" />
        <asp:ImageField DataImageUrlField="IMAGE" DataImageUrlFormatString="~\Images\{0}" HeaderText="Image" ReadOnly="True">
        </asp:ImageField>
        <asp:BoundField DataField="PRICE" HeaderText="Price" ReadOnly="True" />
        <asp:BoundField DataField="QUANTITY" HeaderText="Quantity" />
        <asp:TemplateField HeaderText="Total">
            <ItemTemplate>
                <asp:Label ID="Label1" runat="server" Text='<%# Double.Parse(Eval("PRICE").ToString()) * Int32.Parse(Eval("QUANTITY").ToString()) %>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField ShowHeader="False">
            <EditItemTemplate>
                <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="True" CommandName="Update" Text="Update"></asp:LinkButton>
                &nbsp;<asp:LinkButton ID="LinkButton2" runat="server" CausesValidation="False" CommandName="Cancel" Text="Cancel"></asp:LinkButton>
            </EditItemTemplate>
            <ItemTemplate>
                <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="False" CommandName="Edit" Text="Edit"></asp:LinkButton>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:CommandField ShowDeleteButton="True" />
    </Columns>
</asp:GridView>

I'm usually pretty good at finding answers, but this one has got me stumped.

The site crashes after clicking update because the returned value from int quantity = Int32.Parse(txtQuantity.Text); is "" and obviously you cant parse an int from that.

As for the tag of possible duplicate of "ASP.NET validation error message to change labels text." I was unable to find anything that points me in the direction of an answer.

Answer 1

Call FillData() in Page_PreInit . Otherwise, when the ASP.Net runtime goes to restore ViewState for the grid, including your new Textbox data, there's nowhere to put it yet. Remember that every single server event uses a brand new instance of your page class and must rebuild the entire page from scratch.

Answer 2

This was a royal pain to figure out since I'm just learning ASP.net and C#.

When I was able to make this work on an earlier assignment I wasn't using a Master page, with this project I am. The problem lies in the fact that I am using a <form runat="server"> tag in the Master page. Since you can only have one <form runat="server"> tag per page, my GridView wasn't wrapped in one. Once I removed the Master page and added the <form runat="server"> wrapper around the GridView, everything works as intended.