Android implement search with view model and live data

Question

I\'m working on a project in android for a udacity course I\'m currently trying to implement a search function while adhering to android architecture components and using fi

Answer 1

I faced the same issue and solved it with the answer of @Rohit, thanks! I simplified my solution a bit to illustrate it better. There are Categories and each Category has many Items. The LiveData should only return items from one Category. The user can change the Category and then the fun search(id: Int) is called, which changes the value of a MutableLiveData called currentCategory. This then triggers the switchMap and results in a new query for items of the category:

class YourViewModel: ViewModel() {

    // stores the current Category
    val currentCategory: MutableLiveData = MutableLiveData()

    // the magic happens here, every time the value of the currentCategory changes, getItemByCategoryID is called as well and returns a LiveData
    val items: LiveData> = Transformations.switchMap(currentCategory) { category ->
           // queries the database for a new list of items of the new category wrapped into a LiveData
           itemDao.getItemByCategoryID(category.id)
    }

    init {
        currentCategory.value = getStartCategoryFromSomewhere()
    }

    fun search(id: Int) { // is called by the fragment when you want to change the category. This can also be a search String...
        currentCategory.value?.let { current ->
            // sets a Category as the new value of the MutableLiveData
            current.value = getNewCategoryByIdFromSomeWhereElse(id)
        }
    }
}