Question

I’m trying to get a couple spinners to change dynamically based on their previous spinner selections. I can update the list but when i use adapter.clear() it crashes. Here is my code:

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;

public class CarKitsAct extends Activity{

    ArrayAdapter<String> adMod, adEd;
    String[] models, edition;
    Boolean initSpMan = true;
    Boolean initSpMod = true;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.carkitslayout);

    // Construct TextViews
        TextView textMan = (TextView) findViewById(R.id.textMan);
        textMan.setText(R.string.selectmanufacturer);
        TextView textMod = (TextView) findViewById(R.id.textMod);
        textMod.setText(R.string.selectmodel);
        TextView textEd = (TextView) findViewById(R.id.textEd);
        textEd.setText(R.string.selectedition);

    // Construct Spinners
        Spinner spMan = (Spinner) findViewById(R.id.spMan);
        Spinner spMod = (Spinner) findViewById(R.id.spMod);
        Spinner  spEd = (Spinner) findViewById(R.id.spEd);

    // Construct Manufacturer Spinner Adapter
        ArrayAdapter<CharSequence> adMan;
        adMan = ArrayAdapter.createFromResource(this, R.array.cars, android.R.layout.simple_spinner_item);
        adMan.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spMan.setAdapter(adMan);

    // Set initial values for model and edition spinners
        models = getResources().getStringArray(R.array.AC);
        edition = getResources().getStringArray(R.array.ACAcceca);

    //Construct adapters for models and editions
        adMod = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, models);
        adMod.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        adMod.setNotifyOnChange(true);
        spMod.setAdapter(adMod);

        adEd = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, edition);
        adEd.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        adEd.setNotifyOnChange(true);
        spEd.setAdapter(adEd);

    // Set up listeners for item selection
        spMan.setOnItemSelectedListener(new ManItemSelectedListener());
    }

    public class ManItemSelectedListener implements OnItemSelectedListener {
        public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
            if (initSpMan ==  true) {
                initSpMan = false;
            } else {
                models = getResources().getStringArray(2130968577 + pos);
                adMod.clear();
                adMod.addAll(models);
                adMod.notifyDataSetChanged();               
            }
    }
        public void onNothingSelected(AdapterView<?> parent) {}
    }
}

As you can see I tried using a boolean flag to determine whether the spinners have just been created or not but then when I change a selection it dies.

Answer 1

You are probably getting an UnsupportedOperationException, right? This is because the adapters get initialised with an array of objects, which it interally converts to an AbstractList, which cannot be modified.

To solve your problem, you simply need to feed something that implements the List<?> interface to the adapter. Example:

String[] strings = getResources().getStringArray(R.array.cars);
List<String> items = new ArrayList<String>(Arrays.asList(strings));
ArrayAdapter<String> adMan = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, items);