How to get textbox value from datalist?

Question

I am using datalist to show product id, name and a textbox("Qty") allow user to input order Qty. I got System.NullReferenceException: Object reference not set to an instance of an object error when user click an item to order. My datasource provides only 2 columns (product id and name). I added a textbox("Qty") and a button to the datalist. I can not get the value from the textbox("Qty") to submit. Could it be my datasource does not contain the "Qty" column thus FindControl alway return null value? How do I fix the problem? Thanks. Here is my code:

<asp:DataList ID="DataList1" runat="server" CellPadding="10" DataKeyField="product_id" DataSourceID="SqlDataSource1" RepeatColumns="2">
 <ItemTemplate>
  <asp:Label ID="product_id" runat="server" 
     Text='<%# Eval("product_id") %>' /><br/>
  <asp:Label ID="product_name" runat="server" 
     Text='<%# Eval("product_name") %>' />
 <br />

<asp:TextBox ID="Qty" runat="server"></asp:TextBox>
<asp:Button ID="ButtonAddToCart" runat="server" Text="Add to Cart" CommandName="addtocart2"   OnCommand="DataList1_ItemCommand"
    />  
</ItemTemplate>
</asp:DataList>

Here is the code for the button:

public void DataList1_ItemCommand(object source, System.Web.UI.WebControls.CommandEventArgs e)

{
 var qtytxtbox =  DataList1.FindControl("Qty") as TextBox;
 // qtytxtbox always return null, why?

}

Answer 1

Your handler doesn't look correct. you should use DataListCommandEventArgs as second parameter. so try something like this

Markup:

<asp:DataList ID="DataList1" runat="server" OnItemCommand="DataList1_ItemCommand" vCellPadding="10" DataKeyField="product_id" DataSourceID="SqlDataSource1" RepeatColumns="2">

Then Add command name in button

<asp:Button ID="ButtonAddToCart" runat="server" Text="Add to Cart" CommandName="addtocart2" />  

and code behind

public void DataList1_ItemCommand(object source, DataListCommandEventArgs e)
{
  if(e.CommandName.Equals("addtocart2")
  {
    TextBox qtytxtbox = (TextBox)(e.Item.FindControl("Qty"));
  }
}