angular 2路由器引导懒惰模块

Question

I have some unclarities about angular 2 router guide .

CanDeactivateGuard is used in CrisisCenterRoutingModule which is part of CrisisCenterModule which is lazy loaded by AppRoutingModule (loadChildren: 'app/crisis-center/crisis-center.module#CrisisCenterModule').

The main question: why should CanDeactivateGuard be declared in AppRoutingModule providers? why not to CrisisCenterRoutingModule providers?

The guide's answer is: we also need to add the Guard to our main AppRoutingModule providers so the Router can inject it during the navigation process.

Answer 1

Well, it seems that indeed CanDeactivateGuard could be provided by CrisisCenterRoutingModule too instead of AppRoutingModule. Now the question is why then the guide pointed AppRoutingModule as the one to provide CanDeactivateGuard? The answer I guess is that the CanDeactivateGuard is a service useful to any module and because lazy loaded modules have their own root injector this means it would be created an additional instance of CanDeactivateGuard for any lazy load module that would provide it too. CanDeactivateGuard has no state so it's useless to have more than one instance of it so it's better to put it in AppRoutingModule.