Show tooltip with property value for ListView grid cells

Hello Joe,
In WinForms it is possible to accomplish this task via the ToolTipController component. Here is an example:

C#
using System;  
using DevExpress.ExpressApp;  
using DevExpress.ExpressApp.Win.Editors;  
using DevExpress.Utils;  
using DevExpress.XtraGrid;  
using DevExpress.XtraGrid.Views.Grid;  
using DevExpress.XtraGrid.Views.Grid.ViewInfo;  
using MainDemo.Module.BusinessObjects;  

namespace MainDemo.Module.Win {  
    public class WinViewController1 : ObjectViewController<ListView, Contact> {  
        ToolTipController tooltipController;  
        protected override void OnActivated() {  
            base.OnActivated();  
            tooltipController = new ToolTipController();  
            tooltipController.GetActiveObjectInfo += tooltipController_GetActiveObjectInfo;  
        }  
        protected override void OnViewControlsCreated() {  
            base.OnViewControlsCreated();  
            GridListEditor gridListEditor = View.Editor as GridListEditor;  
            if(gridListEditor != null) {  
                gridListEditor.Grid.ToolTipController = tooltipController;  
            }  
        }  
        void tooltipController_GetActiveObjectInfo(object sender, ToolTipControllerGetActiveObjectInfoEventArgs e) {  
            if(e.SelectedControl is GridControl) {  
                GridView view = ((GridControl)e.SelectedControl).GetViewAt(e.ControlMousePosition) as GridView;  
                if(view == null) return;  
                GridHitInfo hi = view.CalcHitInfo(e.ControlMousePosition);  
                if(hi.HitTest == GridHitTest.RowCell && hi.Column != null && hi.Column.FieldName == "Manager!") {  
                    Contact relatedContact = (Contact)view.GetRowCellValue(hi.RowHandle, hi.Column);  
                    if(relatedContact != null) {  
                        object toolTipInfoIdentifier = String.Format("{0}_{1}_{2}", hi.HitTest.ToString(), hi.RowHandle.ToString(), hi.Column.FieldName);  
                        e.Info = new ToolTipControlInfo(toolTipInfoIdentifier, relatedContact.FullName);  
                    }  
                }  
            }  
        }  
        protected override void OnDeactivated() {  
            base.OnDeactivated();  
            if(tooltipController != null) {  
                tooltipController.GetActiveObjectInfo -= tooltipController_GetActiveObjectInfo;  
                tooltipController = null;  
            }  
        }  
    }  
}  

Visual Basic
Imports System  
Imports DevExpress.ExpressApp  
Imports DevExpress.ExpressApp.Win.Editors  
Imports DevExpress.Utils  
Imports DevExpress.XtraGrid  
Imports DevExpress.XtraGrid.Views.Grid  
Imports DevExpress.XtraGrid.Views.Grid.ViewInfo  
Imports MainDemo.Module.BusinessObjects  

Namespace MainDemo.Module.Win  
    Public Class WinViewController1  
        Inherits ObjectViewController(Of ListView, Contact)  

        Private tooltipController As ToolTipController  
        Protected Overrides Sub OnActivated()  
            MyBase.OnActivated()  
            tooltipController = New ToolTipController()  
            AddHandler tooltipController.GetActiveObjectInfo, AddressOf tooltipController_GetActiveObjectInfo  
        End Sub  
        Protected Overrides Sub OnViewControlsCreated()  
            MyBase.OnViewControlsCreated()  
            Dim gridListEditor As GridListEditor = TryCast(View.Editor, GridListEditor)  
            If gridListEditor IsNot Nothing Then  
                gridListEditor.Grid.ToolTipController = tooltipController  
            End If  
        End Sub  
        Private Sub tooltipController_GetActiveObjectInfo(ByVal sender As Object, ByVal e As ToolTipControllerGetActiveObjectInfoEventArgs)  
            If TypeOf e.SelectedControl Is GridControl Then  
                Dim view As GridView = TryCast(CType(e.SelectedControl, GridControl).GetViewAt(e.ControlMousePosition), GridView)  
                If view Is Nothing Then  
                    Return  
                End If  
                Dim hi As GridHitInfo = view.CalcHitInfo(e.ControlMousePosition)  
                If hi.HitTest = GridHitTest.RowCell AndAlso hi.Column IsNot Nothing AndAlso hi.Column.FieldName = "Manager!" Then  
                    Dim relatedContact As Contact = CType(view.GetRowCellValue(hi.RowHandle, hi.Column), Contact)  
                    If relatedContact IsNot Nothing Then  
                        Dim toolTipInfoIdentifier As Object = String.Format("{0}_{1}_{2}", hi.HitTest.ToString(), hi.RowHandle.ToString(), hi.Column.FieldName)  
                        e.Info = New ToolTipControlInfo(toolTipInfoIdentifier, relatedContact.FullName)  
                    End If  
                End If  
            End If  
        End Sub  
        Protected Overrides Sub OnDeactivated()  
            MyBase.OnDeactivated()  
            If tooltipController IsNot Nothing Then  
                RemoveHandler tooltipController.GetActiveObjectInfo, AddressOf tooltipController_GetActiveObjectInfo  
                tooltipController = Nothing  
            End If  
        End Sub  
    End Class  
End Namespace  

Note that it is possible to display the calculated property in the lookup column as well. Refer to the How to: Specify a Display Member for a Lookup Editor topic to learn how to do this.

In ASP.NET WebForms you can use a solution from the ASPxGridListEditor: ToolTip in Data thread.