Question

following code is throwing a NullPointerException:

public class test extends Activity implements OnItemSelectedListener {
    private TextView explanation;

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

        explanation = (TextView) findViewById(R.id.picker_explanation_text);

        Spinner spinner = (Spinner) findViewById(R.id.spinner);
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                this, R.array.picker_array,
                android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner.setOnItemSelectedListener(new test());
        spinner.setAdapter(adapter);
    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int pos,
            long id) {
        explanation = (TextView) findViewById(R.id.picker_explanation_text);
    }
}

It is thrown because of explanation = (TextView) findViewById(R.id.picker_explanation_text); in the onItemSelected(...) method, but I have no idea why. It is, after all, working in the onCreate(...) method.

Answer 1

Instead of

    spinner.setOnItemSelectedListener(new test());

use

    spinner.setOnItemSelectedListener(this);

You want to use your real activity as the target; you are creating a new object that is never initialized with a context so when it is called it crashes.