Return onPostExecute() String

Question

I have this code:
Mainactivity:

@Override
protected void onCreate(Bundle savedInstanceState) {
...

    btn_login.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            final String user = txt_usuario.getText().toString();
            final String pssw = txt_senha.getText().toString();

            //progressBar.setVisibility(View.VISIBLE);

            LoginBackground lb = new LoginBackground();
            lb.execute(user, pssw);
        }
    });
}

private void retornoLogin(String ret) {

    if (ret.equals("OK"))
    {
        Toast.makeText(this, "Logado com sucesso", Toast.LENGTH_SHORT).show();
    }
    else if (ret.equals("ERRO"))
    {
        Toast.makeText(this, "Login incorreto", Toast.LENGTH_SHORT).show();
    }

}

And this:

Loginbackground:

@Override
protected String doInBackground(String... params) {

    String p1 = params[0];
    String p2 = params[1];

    SistemaHttp sHttp = new SistemaHttp(null);
    String logado = sHttp.retornaUsuario(p1, p2);

    return logado;
}

@Override
protected void onPostExecute(String str)
{
    Log.d("TESTE","(LoginBackground) onPostexecute(" + str + ")");
}

To MainActivity sending two parameters(user and password) to the class LoginBackground which checks through the class SistemaHttp if there is a registered user with this data in the database. If there is one, the class SistemaHttp returns to the doInBackground a String to "OK".
So I wanted to take this String and pass it on to the MainActivity to throw it in the way RetornoLogin() and display a Toast according to the answer that came. Obs: everything is working until the onPostExecute, I put a Log() to display the doInBackground() and it displays normal OK, just do not know proceed from then on.

Answer 1

Declare an interface in the class Loginbackground:

public interface OnLoginCompletedListener{
    void onLoginCompleted(String result);
}

Add an instance variable:

private OnLoginCompletedListener onLoginCompletedListener;

Declare a new method:

public void setOnLoginCompletedListener(OnLoginCompletedListener onLoginCompletedListener){
    this.onLoginCompletedListener = onLoginCompletedListener;
}

Change the onPostExecute() for:

@Override
protected void onPostExecute(String str)
{
    if(onLoginCompletedListener != null){
       //Chama o listener passando a string
        onLoginCompletedListener.onLoginCompleted(str);
    }
}

Make the Activity who uses Loginbackgroud implement the interface OnLoginCompletedListener

Implement the interface:

@Override
void onLoginCompleted(String result){

    //Chame o método retornoLogin()
    retornoLogin(result);

    //Ou se preferir passe para a aqui o seu código
}

After creating the instance of Loginbackgroud use your method setOnLoginCompletedListener() for "set" the Listener:

-----
LoginBackground lb = new LoginBackground();
lb.setOnLoginCompletedListener(MainActivity.this);
lb.execute(user, pssw);

The method onLoginCompleted() of Activity will be called when onPostExecute() be executed.