error retrieving data from firebase with KOTLIN

Question

I'm trying to retrieve data from firebase, but I get:

java.lang.ClassCastException: java.util.HashMap cannot be cast to com.android.mlc.model.Usuario

I don't know why the cast fails:

private fun listarDatos() {

    databaseReference.child("Usuario").addValueEventListener(object : ValueEventListener{
        override fun onCancelled(p0: DatabaseError) {
            Toast.makeText(baseContext, "Failed to load post.",
                Toast.LENGTH_SHORT).show()
        }

        override fun onDataChange(dataSnapshot: DataSnapshot) {

            Log.w("Usuarios1", "mehe")
            for (UsuariosFirebase in dataSnapshot.children) {
                  listaUsuarios.add(UsuariosFirebase.value as Usuario) <--- ERROR
      

                arrayAdapterUusuario = ArrayAdapter<Usuario>(this@MainActivity,android.R.layout.simple_list_item_1, listaUsuarios)
                listaV_Usuarios.adapter = arrayAdapterUusuario
            }


        }
    })
}

Why can't I cast the value UsuarioFireBase.value to Usuario?

Please edit your question and add your database structure as a screenshot. Please respond with @AlexMamo — Alex Mamo
– Alex Mamo, Commented Jul 6, 2020 at 11:02
Seems to be the same case. stackoverflow.com/questions/46957319/… — cnux9
– cnux9, Commented Feb 18, 2021 at 9:32

Frank van Puffelen · Accepted Answer · 2020-07-06 18:17:23Z

1

As far as I can see, your UsuariosFirebase.value returns a Map<String, Object>, which indeed can't be cast to Usuario as the error indicates.

To get the data from the DataSnapshot as a Usuario object, you will have to tell Firebase to do that conversion for you:

listaUsuarios.add(UsuariosFirebase.getValue<Usuario>())

Also see the documentation on getting values from Firebase.

The above requires that you have the Kotlin extensions (KTX) for Firebase Realtime Database installed. If you're having a hard time making that work, you can also use this variant, which is a pretty direct rewrite of the Java code:

listaUsuarios.add(UsuariosFirebase.getValue(Usuario::class.java))

edited Jul 6, 2020 at 18:17

answered Jul 6, 2020 at 14:52

Frank van Puffelen

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3 Comments

darkblade60 Over a year ago

no type arguments expected for fun getValue: Any? ... im gonna cry

Frank van Puffelen Over a year ago

Can you try listaUsuarios.add(UsuariosFirebase.getValue(Usuario::class.java))? That's what I've seen used elsewhere, but my answer is based on what the documentation suggest.

darkblade60 Over a year ago

yes, ty bro, UsuariosFirebase.getValue(Usuario::class.java) works fine :)

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