public class MainComboBox extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

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

        Button myButton =(Button)findViewById(R.id.button1);
        myButton.setOnClickListener(new Button.OnClickListener() {
            public void onClick(View v) {
            	
            Spinner sp =	(Spinner)findViewById(R.id.spinner);
            String spinnerString = null;
            spinnerString = sp.getSelectedItem().toString();
            int nPos = sp.getSelectedItemPosition();
            
             
                Toast.makeText(getApplicationContext(), "getSelectedItem=" + spinnerString,
                    Toast.LENGTH_LONG).show();
                Toast.makeText(getApplicationContext(), "getSelectedItemPosition=" + nPos,
                		Toast.LENGTH_LONG).show();
            }
        });
    }
}

public  class MyOnItemSelectedListener implements OnItemSelectedListener {

    public void onItemSelected(AdapterView<?> parent,
        View view, int pos, long id) {
      Toast.makeText(parent.getContext(), "Item is " +
          parent.getItemAtPosition(pos).toString(), Toast.LENGTH_LONG).show();
    }

    public void onNothingSelected(AdapterView parent) {
      // Do nothing.
    }
}

<resources>
    <string name="hello">Hello World, MainComboBox!</string>
    <string name="app_name">ComboBox</string>
    <string name="prompt">Choose a country</string>
    <string-array name="countries_array">
        <item>China</item>
        <item>India</item>
        <item>USA</item>
        <item>Indonesia</item>
        <item>Brazil</item>
        <item>Pakistan</item>
        <item>Nigeria</item>
        <item>Bangladesh</item>
        <item>Russia</item>
    </string-array>    
</resources>

<LinearLayout xmlns:android="//schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:padding="10dip"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content">
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dip"
        android:text="@string/prompt"
    />
    <Spinner 
        android:id="@+id/spinner"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:prompt="@string/prompt"
    />
    <Button android:text="Button" android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>

</LinearLayout>