Question

I am making an android app, where, during startup I disable the pauze button of the media player. After the ok button is clicked (and music starts to play), I want to enable the pauze button.

This code works fine, except for the last line (I did delete some non-relevant lines). That gives me a runtime error (NullPointerException).

I used MainActivity.this to access the button. What am I doing wrong?

Thank you for any help!

public class MainActivity extends Activity {

    // initialise variables
    TextView textOut;
    MediaPlayer mediaPlayer;
    Button buttonPauze;
    Button ok;

    // *******************************************************
    // set Layout - on create
    // *******************************************************
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textOut = (TextView) findViewById(R.id.textView1);


        // *******************************************************
        // set the play, generate and pauze buttons
        // *******************************************************
        Button buttonPauze = (Button) findViewById(R.id.buttonPauze);
        Button ok = (Button) findViewById(R.id.buttonStart);

        buttonPauze.setOnClickListener(buttonPauseOnClickListener);
    buttonPauze.setEnabled(false);
    ok.setEnabled(true);

    // *******************************************************
    // on click generate
    // *******************************************************
    ok.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            MainActivity.this.buttonPauze.setEnabled(true);

Answer 1

Replace:

Button buttonPauze = (Button) findViewById(R.id.buttonPauze);

with:

buttonPauze = (Button) findViewById(R.id.buttonPauze);

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Basically, you had 2 buttonPauze‘s, one as local variable and the other as a class field. By removing the Button, you are using the class field buttonPauze locally and assign a proper object to it.

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Same thing with ok!