Android (Kotlin): Type mismatch in Observer

Question

I am implementing an MVVM Android architecture in which in the main application component ( MainActivity ), I listen to the ModelView 's LiveData storage for any changes. However, in the following piece of code:

private final var viewModel:ScheduleViewModel = ViewModelProviders.of(this).get(ScheduleViewModel::class.java)

viewModel.getSchedule().observe(this, object:Observer<String> {
    fun onChanged(feed:String){
    }
})

I get the following error:

Required: Observer<in String!>
Found: 

Below are my imports:

import android.os.Build
import android.os.Bundle
import android.util.Base64
import androidx.annotation.Nullable
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.ViewModelProviders
import androidx.loader.app.LoaderManager
import androidx.loader.content.Loader
import androidx.viewpager.widget.ViewPager
import com.example.mvvmarchitecture.ui.main.TabsAdapter
import com.google.android.material.tabs.TabLayout
import java.io.InputStream
import java.net.HttpURLConnection
import java.net.URL
import java.util.*

Answer 1

To fix that, replace Observer<String> with Observer<in String> .

But even easier, use a lambda instead of an anonymous object, so you don't have to worry about matching up the type:

viewModel.getSchedule().observe(this) { feed ->
    //...
}

Answer 2

What does viewModel.getSchedule() return? if your function is defined like this

fun getSchedule():MutableLiveData<String>(){
// your code
return liveDataOfString
}

this it should compile.

viewModel.getSchedule().observe(this, object :androidx.lifecycle.Observer<in String> {
            override fun onChanged(t: String?) {
                TODO("Not yet implemented")
            }

        })

https://kotlinlang.org/docs/generics.html