public bool Allow { get; set; }

Public Property Allow As Boolean

using DevExpress.XtraGrid.Views.Grid;

gridView1.EditFormShowing += new EditFormShowingEventHandler(OnEditFormShowing);
//...
private void OnEditFormShowing(object sender, EditFormShowingEventArgs e) {
    GridView view = sender as GridView;
    if (view == null) return;
    if (view.GetRowCellValue(e.RowHandle, "ShipCountry").ToString() == "France") e.Allow = false;
}

Imports DevExpress.XtraGrid.Views.Grid

AddHandler GridView1.EditFormShowing, AddressOf OnEditFormShowing
'...
Private Sub OnEditFormShowing(sender As Object, e As EditFormShowingEventArgs)
    Dim view As GridView = TryCast(sender, GridView)
    If view Is Nothing Then
        Return
    End If
    If view.GetRowCellValue(e.RowHandle, "ShipCountry").ToString() = "France" Then
        e.Allow = False
    End If
End Sub

async void GridView1_EditFormShowing(object sender, DevExpress.XtraGrid.Views.Grid.EditFormShowingEventArgs e) {
    e.Allow = false;
    var row = gridView1.GetRow(e.RowHandle) as DevExpress.Data.Async.Helpers.ReadonlyThreadSafeProxyForObjectFromAnotherThread;

void GridView_EditFormShowing(object sender, DevExpress.XtraGrid.Views.Grid.EditFormShowingEventArgs e) {
    e.Allow = false;

Private Sub GridView_EditFormShowing(ByVal sender As Object, ByVal e As Views.Grid.EditFormShowingEventArgs)
    e.Allow = False
    Dim employee As Employee = Nothing