从 listView Firebase 中删除项目

Question

I have this problem when i open the view of "Eventos", im trying to delete from de database the selected items from the listview.

enter image description here

public class ShowData extends AppCompatActivity {

DatabaseReference databaseReference;
ListView listView;
ArrayList<String> arrayList = new ArrayList<>();
ArrayAdapter<String> arrayAdapter;
Button btnDelete;
Module module;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_show_data);
    databaseReference = FirebaseDatabase.getInstance().getReference("Eventos");
    listView = (ListView) findViewById(R.id.listViewShow);
    btnDelete = (Button) findViewById(R.id.btnBorrarElemento);
    module=((Module)getApplication());
    arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, arrayList);
    listView.setAdapter(arrayAdapter); .....


... listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> paramAdapterView, View view, int position, long id) {
            module.setGvalue_titulo(arrayList.get(position));
            module.setGvalue_descripcion(arrayList.get(position));
            module.setGvalue_fecha(arrayList.get(position));
            module.setGvalue_url(arrayList.get(position));
        }
    });


    btnDelete.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
            final String str = module.getGvalue_titulo().substring(0, 6);
            if(str == ""){
                Toast.makeText(ShowData.this, "No se ha seleccionado ningun elemento para eliminar", Toast.LENGTH_SHORT).show();
            }
            else {
                databaseReference.child("Eventos").child(str).addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        databaseReference.child(str).removeValue();
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError databaseError) {

                    }
                });
                Toast.makeText(ShowData.this, "Evento Eliminado", Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(getApplicationContext(),ShowData.class);
                startActivity(intent);
            }
        }
    }); ....

The module have the getters and setters necesaries: enter image description here

In my manifest i have this: enter image description here

Answer 1

Your problem is that you are trying to cast your Application to Module , but it's not Module . Well, have you registered your Module as custom application implementation in your AndroidManifest.xml ? If the answer is "no" than this is the exact reason! Follow this answer to check how to do it easily.