ListView displays nothing

Question

I would like to send selected item from listview to another listview with sharedprefences. I can save item but cannot see this item another listview. Activity class

TextView textUrun = (TextView) view.findViewById(R.id.textUrun);
            TextView textFiyat = (TextView) view.findViewById(R.id.textFiyat);
            String yemek = textUrun.getText().toString();
            String fiyat = textFiyat.getText().toString();
            DataProvider dataProvider = new DataProvider(yemek,fiyat);
            list.add(dataProvider);
            String jsonurun = gson.toJson(list);
            SharedPreferences sharedPreferences = getSharedPreferences("yemekbilgi", Context.MODE_PRIVATE);
            SharedPreferences.Editor editor = sharedPreferences.edit();
            editor.putString("yemek",jsonurun);
            editor.apply();
            Toast.makeText(getApplicationContext(),"Listeye Kaydedildi",Toast.LENGTH_LONG).show();

This is list class which should display items.Listele1

SharedPreferences sharedPreferences = getSharedPreferences("urun1", Context.MODE_PRIVATE);
    List<DataProvider> list;
    String jsonurun = sharedPreferences.getString("liste1", "");
    Gson gson = new Gson();
    DataProvider[] providers = gson.fromJson(jsonurun, DataProvider[].class);
    list = Arrays.asList(providers);
    listDataAdapter = new ListDataAdapter(getApplicationContext(), list);
    listView = (ListView) findViewById(R.id.liste1);
    listView.setAdapter(listDataAdapter);

Finally,this is Adapter Class

public class ListDataAdapter extends ArrayAdapter {
List list = new ArrayList();

public ListDataAdapter(@NonNull Context context,List<DataProvider> list) {
    super(context, R.layout.be_layout, list);
}

static class LayoutHandler{
    TextView ad,fiyat;
}

@Override
public void add(@Nullable Object object) {
    super.add(object);
    list.add(object);
}

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

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

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    View view = convertView;
    LayoutHandler layoutHandler;
    if (view == null){
        LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = layoutInflater.inflate(R.layout.child_layout,parent,false);
        layoutHandler = new LayoutHandler();
        layoutHandler.ad = (TextView) view.findViewById(R.id.textUrun);
        layoutHandler.fiyat = (TextView) view.findViewById(R.id.textFiyat);
        view.setTag(layoutHandler);
    }
    else
        layoutHandler = (LayoutHandler) view.getTag();
    DataProvider dataProvider = (DataProvider) this.getItem(position);
    layoutHandler.ad.setText(dataProvider.getAd());
    layoutHandler.fiyat.setText(dataProvider.getFiyat());
    return view;
}

}

Answer 1

You passed in a List, but you never assigned it.

public class ListDataAdapter extends ArrayAdapter<DataProvider> {
    List<DataProvider> list;  // don't assign here 

    public ListDataAdapter(@NonNull Context context, @LayoutRes int resource,List<DataProvider> list) {
        super(context, resource, list);
        this.list = list;   // see here 
    }

It's worth pointing out, though, that you could also not do the above and entirely remove list, add(), and getItem(), getCount() definitions, then it'll likely work.

Any usage of list.get(position) should instead be getItem(position)

Answer 2

    list = new ArrayList<DataProvider>();
    listView = (ListView) findViewById(R.id.liste1);
    listDataAdapter = new ListDataAdapter(getApplicationContext(),R.layout.child_layout,list);
    gson = new Gson();

    SharedPreferences sharedPreferences = getSharedPreferences("yemekbilgi", Context.MODE_PRIVATE);
    String yemek = sharedPreferences.getString("yemek","");
    Type type = new TypeToken<List<DataProvider>>(){}.getType();
    list.addAll(gson.fromJson(yemek,type));
    listView.setAdapter(listDataAdapter);
    listDataAdapter.notitifyDataSetChanged();

Answer 3

list = new ArrayList<DataProvider>();
gson = new Gson();
SharedPreferences sharedPreferences = getSharedPreferences("yemekbilgi", Context.MODE_PRIVATE);
String yemek = sharedPreferences.getString("yemek","");
Type type = new TypeToken<List<DataProvider>>(){}.getType();
list = gson.fromJson(yemek,type);
listView = (ListView) findViewById(R.id.liste1);
listDataAdapter = new ListDataAdapter(getApplicationContext(),R.layout.child_layout,list);
listView.setAdapter(listDataAdapter);