error casting button in datagrid

Hughesie78 · May 1st, 2008, 09:11 AM

this line of code gives me the error( CS0266: Cannot implicitly convert type 'System.Web.UI.Control' to 'System.Web.UI.WebControls.Button'. An explicit conversion exists (are you missing a cast?))

Button deleteButton = e.Item.Cells[0].Controls[0];

I then change to cast :
Button deleteButton = (Button)e.Item.Cells[0].Controls[0];

and get the following error:
Specified argument was out of the range of valid values.
Parameter name: index
this is a handler on a datagrid to delete files, here is the entire code:
void articleList_ItemDataBound(object sender, DataGridItemEventArgs e) {
        // First, make sure we're NOT dealing with a Header or Footer row
        if (((e.Item.ItemType != ListItemType.Header)
                    && (e.Item.ItemType != ListItemType.Footer))) {
            // Now, reference the Button control that the Delete ButtonColumn
            // has been rendered to
            Button deleteButton = e.Item.Cells[0].Controls[0];
            // We can now add the onclick event handler
            deleteButton.Attributes["onclick"] = ("javascript:return " + ("confirm(\'Are you sure you want to delete the file "
                        + (DataBinder.Eval(e.Item.DataItem, "Name") + "?\')")));
        }
    }

any ideas?

samjudson · May 1st, 2008, 09:21 AM

Often you will have additional 'invisible' controls in a cell, usually just LiteralControl instances for padding.

Double check how many controls are in the e.Item.Cells[0].Controls.Count, and if its 3 - then pick the middle one (i.e. e.Item.Cells[0].Controls[1]).

Otherwise you'll have to loop through until e.Item.Cells[0].Controls[i] is Button is true.

/- Sam Judson : Wrox Technical Editor -/

planoie · May 2nd, 2008, 08:04 AM

Also, do you have a pager active? You are not filtering out that item type. I find it easier to do something like this (please excuse incorrect syntax, doing this from memory):

Code:

switch(e.Item.ItemType){
  case ListItemType.Item:
  case ListItemType.AlternateItem:
    //do work here
    break;
}

Regarding getting at the control itself, I find it less problematic to use the ID of the control. So inside the item template you have a control:

Code:

    <asp:button runat="server" id="btnMyButton" />

Then in your codebehind:

Code:

    Button myButton = (Button)e.Item.FindControl("btnMyButton");

This will find the button anywhere in the item, regardless of cell. This greatly reduces bugs and maintenance issues if you want to move things around.

-Peter
peterlanoie.blog