I have created a singleton service sidenavservice to get reference to mat sidenav using viewchild this way i can control like open close toggle etc sidenav from anywhere in the app. Estoy implementando en mi proyecto el ejemplo de sidenav de kenji 1996 link de su repositorio. To toggle a sidenav from another component you need.
This Article Is About Creating Sidenav Component Using Angular Material 6 With Routing Along With Mat Toolbar The Different Routes Wi Angular Material It Works