How to handle data entered into a fragment of a Tabbed Activity in Android Studio

Question

I am learning to develop using Android Studio and I am with a beginner’s question: which class I perform data processing from a click of a fragment in a Tabbed Activity. To illustrate simply, I created a simple application using Tabbed Activity with a fragment containing an Edit text and a button. In the code of the screen, I try to call from the click of the button a class called "saved":

 <Button
    android:id="@+id/button3"
    android:layout_width="88dp"
    android:layout_height="48dp"
    android:layout_marginStart="132dp"
    android:layout_marginTop="61dp"
    android:layout_marginEnd="191dp"
    android:layout_marginBottom="382dp"
    android:text="Button"
    android:onClick="salvaDados"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/editText" />

The idea (at the moment) is simply to test the value of Edit text, with the following code:

     public void salvaDados(){
        Button botao = findViewById(R.id.button3);
        EditText texto = findViewById(R.id.editText);
        if(texto.getText().length() == 0){
            Toast.makeText(getApplication(),"nao tem nada",Toast.LENGTH_SHORT).show();
        }
        else
            Toast.makeText(getApplication(),"tem dados",Toast.LENGTH_SHORT).show();

    }

The question is, in what class do I treat it? 1. I tried to create the above class in fragment "mother activity" and gave error; 2. I tried to create a separate class only to process fragment data and also gave error. 3. the above example is just for me to know where I should treat all the code, since later I will do more complex things like save the data in the database, generate graphs on other screens, etc.

It has at least 15 hours that I am trying to solve this and I could not find any tutorial to help. Can someone give me a light? Thanks for your help!

Answer 1

Here is an example of the fragment class you can use:

public class seuFragmento extends Fragment {


    private View view;
    private Activity activity;

    public void onAttach(Context context) {
        super.onAttach(context);
        activity = (Activity) context;
    }

    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.seu_layout_fragment, container, false);

        salvaDados();

        return view;
    }
    public void salvaDados(){
        Button botao = view.findViewById(R.id.button3);
        EditText texto = view.findViewById(R.id.editText);
        if(texto.getText().length() == 0){
            Toast.makeText(activity,"nao tem nada",Toast.LENGTH_SHORT).show();
        }
        else
            Toast.makeText(activity,"tem dados",Toast.LENGTH_SHORT).show();

    }
}

You use the view raised in onCreateView to call findViewById. Use the context raised in onAttach to use in the toast. In the view changes R.layout.seu_layout_fragment to its own layout.