如何在组件中使用可观察的主题变量？

I have a shared service with providers in my root component. I an using this service to manipulate parent for the count of items selected. On the parent this count is surrounded by anchor so it takes user to all items selected. However i am using a variable of shared service to do this, while i believe there should be some way so that i can call observable to fetch the info. My code for service isI have a shared service with providers in my ro