Android : How to put models (not strings) into spinner

I'm trying to put models into spinner. But the problem is that the spinner is empty after I put adapter with models.

Here is model:

public Model {
    private String mId;

    private String mTitle;

    public String getId() {
        return mId;
    }

    public String getTitle() {
        return mTitle;
    }
}

Adapter where I can put models:

public class ModelSpinnerAdapter extends ArrayAdapter<String> {

    private List<Model> mModels;

    public ModelSpinnerAdapter(Context context, int resource, int textViewId, List<Model> models) {
        super(context, resource, textViewId);

        mModels = models;
    }

    @Override
    public String getItem(int position) {
        Model model = mModels.get(position);

        return model.getTitle();
    }
}

Here's I put adapter into spinner:

private void initSpinner(View view) {
    Spinner spinner = (Spinner) view.findViewById(R.id.spinner);

    ModelSpinnerAdapter adapter = new ModelSpinnerAdapter(getActivity(), 
        android.R.layout.simple_spinner_item, android.R.id.text1, getModels());

    spinner.setAdapter(adapter);
    adapter.notifyDataSetChanged();
}

But, when I run app, the spinner is empty. What's wrong?