sapui5 - Popup - Navigate to another xml view

Dear UI5 experts

I am extending an fiori app and have replaced a view and placed a popup. Now my requirement is when I click the close button in the popup I want to open an xmlview.

code.

sap.m.MessageBox.error( "Error Message - some error", 
{ icon: sap.m.MessageBox.Icon.ERROR, title: "Confirmation Error", onClose: function (oAction) { <br> this.router = sap.ui.core.UIComponent.getRouterFor(this); <br>this.router.navTo("customview"); } } );

can some one pls advise on the error I am getting.

'navTo' of undefined