Call more than one callback at a time

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I need a WorkerClass that generates sequential numbers to print through a Callback Interface these numbers in the MainActivity and in a SegundaActivity when opened. My problem is that when SegundaActivity is open the MainActivity no longer receives the numbers that are being generated in the WorkerClass. Here is my code:

  

Class MainActivity 

public class MainActivity extends AppCompatActivity implements MeuCallback {

    private Button button1;

    private MinhaWorkerClass minhaWorkerClass;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        button1 = (Button) findViewById(R.id.button1);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, SegundaActivity.class);
                startActivity(intent);
            }
        });

        minhaWorkerClass = minhaWorkerClass.getInstancia();
        if (minhaWorkerClass != null) {
            minhaWorkerClass.criaCallback(this);
        }
    }

    @Override
    public void imprimeNumero(int numero) {
        Log.i("Rute", "MainActivity-Numero: " + numero);
    }
}
  

Classe SegundaActivity 

public class SegundaActivity extends AppCompatActivity implements MeuCallback {

    private MinhaWorkerClass minhaWorkerClass;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_segunda);

        minhaWorkerClass = minhaWorkerClass.getInstancia();
        if (minhaWorkerClass != null) {
            minhaWorkerClass.criaCallback(this);
        }
    }

    @Override
    public void imprimeNumero(int numero) {
        Log.i("Rute", "SegundaActivity-Numero: " + numero);
    }
}
  

Class MyWorkerClass 

public class MinhaWorkerClass {

    private MeuCallback meuCallback;

    private static MinhaWorkerClass instancia;

    // Construtor privado:
    private MinhaWorkerClass() {

        constroiSequenciaNumeros();
    }

    public static synchronized MinhaWorkerClass getInstancia() {
        if (instancia == null) {
            instancia = new MinhaWorkerClass();
        }

        // Retorna sempre a unica instancia criada desta Classe:
        return instancia;
    }

    public void criaCallback(MeuCallback meuCallback){
        this.meuCallback = meuCallback;
    }

    private void constroiSequenciaNumeros() {

        new Thread(new Runnable() {
            @Override
            public void run() {

                for (int i = 0; i < 1000; i++) {

                    if (meuCallback != null) {
                        meuCallback.imprimeNumero(i);
                    }
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }
}
  

Interface MyCallback 

public interface MeuCallback {

    void imprimeNumero(int numero);
}
    
asked by anonymous 31.01.2018 / 00:00

1 answer

2

The MyWorkerClass class, as implemented, can only register a callback .

In order to register more than one you have to save them to an array. 

public class MinhaWorkerClass {

    private ArrayList<MeuCallback> callbacks = new ArrayList<>();

    ...
    ...

    public void addCallback(MeuCallback callback){

        if(!callbacks.contains(callback)){
            callbacks.add(callback);
        }
        return;
    }

    public void removeCallback(MeuCallback callback){

        callbacks.remove(callback);
        return;
    }

    private void constroiSequenciaNumeros() {

        new Thread(new Runnable() {
            @Override
            public void run() {

                for (int i = 0; i < 1000; i++) {

                    //Percorre o ArrayList e chama imprimeNumero()
                    //em todos os callbaks registados.

                    for(MeuCallback meuCallback : calbacks) {
                        meuCallback.imprimeNumero(i);
                    }

                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }
}

NOTE: This implementation can cause memory leak if the class that implements MyCallback is an Activity / Fragment and these are destroyed / recreated by Android, this will happen, for example, whenever there is rotation the device. To avoid this situation use minhaWorkerClass.removeCallback(this) in method onDestroy() . Note that there are situations where onDestroy () might not be called.

    
31.01.2018 / 11:53
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