Cant populate a spinner

Question

Hello i know this has been posted before but i cannot seem able to find the mistake. i have created a List<Objects> with which i want to populate a spinner. My code

public class RegisterActivity extends AppCompatActivity {

    private Toolbar tb;
    private Spinner spinner;
    private List<Swmata> lista;
    private BaseAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);
        spinner = (Spinner)findViewById(R.id.spinner3);
        tb = (Toolbar)findViewById(R.id.toolBar);
        lista = new ArrayList<Swmata>();
        tb.setTitle("Λελέμετρο");
        setSupportActionBar(tb);
        populateSpinner();
        adapter = new MyAdapter(RegisterActivity.this, lista);
        spinner.setAdapter(adapter);
    }

    private void populateSpinner() {
        lista.add(new Swmata(R.drawable.peziko, "Πεζικό(ΠΖ)"));
        lista.add(new Swmata(R.drawable.eidikesdinameis, "Ειδικές Δυνάμεις(ΕΔ)"));
        lista.add(new Swmata(R.drawable.tethwrakismena, "Τεθωρακισμένα(ΤΘ)"));
        lista.add(new Swmata(R.drawable.piroboliko, "Πυροβολικό(ΠΒ)"));
        lista.add(new Swmata(R.drawable.mixaniko, "Μηχανικό(ΜΧ)"));
        lista.add(new Swmata(R.drawable.aeroporia, "Αεροπορία Στρατού(ΑΣ)"));
        lista.add(new Swmata(R.drawable.texniko, "Τεχνικό(ΤΧ)"));
        lista.add(new Swmata(R.drawable.efodiasmou, "Εφοδιασμού Μεταφορών(ΕΜ)"));
        lista.add(new Swmata(R.drawable.ylikou, "Υλικού Πολέμου(ΥΠ)"));
        lista.add(new Swmata(R.drawable.ygeionomiko, "Υγειονομικό(ΥΓ)"));
        lista.add(new Swmata(R.drawable.diabibaseis, "Διαβιβάσεων(ΔΒ)"));
        lista.add(new Swmata(R.drawable.stratonomia, "Στρατονομία(ΣΝ)"));
    }

The Adapter:

public class MyAdapter extends BaseAdapter {

    private List<Swmata> objects;
    private Context context;

    public MyAdapter(Context context, List objects) {
        this.context = context;
        this.objects = objects;
    }

    @Override
    public int getCount() {
        return objects.size();
    }

    @Override
    public Object getItem(int position) {
        return objects.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        SwmataHolder holder;

        if (convertView == null){
            LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            inflater.inflate(R.layout.spinner_item, parent, false);
            holder = new SwmataHolder();
            holder.imageView = (ImageView)convertView.findViewById(R.id.imageSpinner5);
            holder.textView = (TextView)convertView.findViewById(R.id.textSpinner5);
            convertView.setTag(holder);
        }else {
            holder = (SwmataHolder)convertView.getTag();
        }

        Swmata swma = (Swmata) getItem(position);
        holder.imageView.setImageResource(swma.getImage());
        holder.textView.setText(swma.getName());
        return convertView;
    }

    static class SwmataHolder{
        ImageView imageView;
        TextView textView;
    }
}

The Error:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
            at com.project.matrix.lelemetroga.MyAdapter.getView(MyAdapter.java:46)

line 46: holder.imageView = (ImageView)convertView.findViewById(R.id.imageSpinner5);

The layout file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:padding="15dp"
    android:layout_height="wrap_content">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/aeroporia"
        android:layout_weight="1"
        android:id="@+id/imageSpinner5" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:layout_weight="1"
        android:id="@+id/textSpinner5" />
</LinearLayout>

Now i dont know what i have been doing wrong but since i used the same methods in other projects it actually looks so funny that i cannot find my mistake. If anyone can point it out i would rather appreciated. Thanks in advance!!!

Answer 1

You need

convertView = inflater.inflate(R.layout.spinner_item, parent, false);

in your if statement.

You get a NPE on convertView.findViewById() because you never initialized convertView so it is null the first time. You need to give it a value when inflating your View.

Answer 2

You forget to assign the inflated value to the convertView variable.

This:

inflater.inflate(R.layout.spinner_item, parent, false);

should be this:

convertView = inflater.inflate(R.layout.spinner_item, parent, false);

Answer 3

In this snippet, you test if convertView is null, but then you go ahead and dereference it:

    if (convertView == null){
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        inflater.inflate(R.layout.spinner_item, parent, false);
        holder = new SwmataHolder();
        holder.imageView = (ImageView)convertView.findViewById(R.id.imageSpinner5);
        holder.textView = (TextView)convertView.findViewById(R.id.textSpinner5);
        convertView.setTag(holder);
    }else { 

I think you meant to assign a value to convertView, like this:

    if (convertView == null){
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.spinner_item, parent, false);
        holder = new SwmataHolder();
        holder.imageView = (ImageView)convertView.findViewById(R.id.imageSpinner5);
        holder.textView = (TextView)convertView.findViewById(R.id.textSpinner5);
        convertView.setTag(holder);
    }else {