How to show Toast message in Preview of Lightning Application in Salesforce?

I am using:

showToast : function(component, event) {
        var toastEvent = $A.get("e.force:showToast");
        toastEvent.setParams({
            message:'This account does not have any contacts.',
        });
        toastEvent.fire();
    }

but this gives me an error. How can I use this in preview?