public int obtenerCombinacionAleatoria() {

    ArrayList<Integer> listaNumeros = new ArrayList();
    int totalNumerosAgenerar = 0;
    int numero = 0;

    while (totalNumbersToGenerate != 4) {
        number = ((int) (Math.random() * 6) + 1);
        if (!listNumbers.contains(number)) {
            totalNumbersToGenerate++;
            listNumbers.add(number);

        }
        if (number == 1) {
            imageButton1.setImageResource(R.drawable.yellow);
        }
        if (number == 2) {
            imageButton2.setImageResource(R.drawable.blue);
        }
        if (number == 3) {
            imageButton3.setImageResource(R.drawable.purple);
        }
        if (number == 4) {
            imageButton4.setImageResource(R.drawable.red);
        }
        if (number == 5) {
            imageButton3.setImageResource(R.drawable.pink);
        }
        if (number == 6) {
            imageButton1.setImageResource(R.drawable.green);
        }
    }
    return 0;

}