Пока решил проблему таким способом:
Ext.define("EwsOffice.view.altawin.grorders.Grorders", {
extend: "Ext.grid.Panel",
...
bind: { selection: "{selection}" },
viewModel: { data: { selection: null } },
tbar: [{
text: "Import",
handler: "onImportButtomClick",
bind: {
disabled: "{!selection}"
}
}],