Sorry, I'm not really sure what i was thinking, don't use databinding, use the Init event instead....
onInit="BtnDelete_Init"
VB
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Protected Sub BtnDelete_Init(ByVal sender As Object, ByVal e As EventArgs)
Dim BtnDelete As ImageButton = CType(sender, ImageButton)
BtnDelete.Attributes.Add("onclick", "javascript: return confirm('Are you sure you wish to delete this item?');")
End Sub
C#
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protected void BtnDelete_Init(Object sender, EventArgs e)
{
ImageButton BtnDelete = (ImageButton) sender
BtnDelete.Attributes.Add("onclick","javascript: return confirm('Are you sure you wish to delete this item?');")
}