IONIC4新特性-生命周期方法

The CanActivate and CanDeactivate interfaces can be used to implement the same type of logic that the removed events ionViewCanEnter and ionViewCanLeave did.

例子：

@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private authService: AuthService) {}

  canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot) {
    return this.authService.isAuthenticated();
  }
}