Custom NumberPicker buttons.onClickListener

Question

One of my activities requires a list view with custom number pickers in each row. I created the number picker as suggested here. When I click on the buttons, however, the counter doesn't increment or decrement at all.

The following is the code found at my Custom ListView Adapter.

public class MaterialListViewAdapter extends BaseAdapter 
{
    ViewHolder holder;
    int counter = 0;

    private ArrayList<MaterialClass> data;

    public static LayoutInflater inflater = null;

    public static Dialog dialog;
    String materialName;

    public MaterialListViewAdapter(Context applicationContext,
       int materialdialogcontent, ArrayList<MaterialClass> materials) 
    {
       this.data = materials;
        inflater = (LayoutInflater)applicationContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }


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

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

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

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

        View vi = convertView;

        //ViewHolder holder = new ViewHolder();

        if(vi == null)
        {
            holder = new ViewHolder();

            vi = inflater.inflate(R.layout.materialdialogcontent, null);

            //Initialize Buttons and TextViews.

            holder.num.setText("0");

            holder.add.setOnClickListener(new View.OnClickListener()
            {
                @Override
                public void onClick(View v) 
                {
                    counter++;
                    holder.num.setText("" + counter);
                }
            });

            holder.sub.setOnClickListener(new View.OnClickListener()
            {   
                @Override
                public void onClick(View v) 
                {
                    counter--;
                    holder.sub.setText("" + counter);
                }
            });


            //holder.pk = (NumberPicker)vi.findViewById(R.id.npMaterialAmount);

            vi.setTag(holder);
        }
        else
        {
        holder = (ViewHolder)vi.getTag();
        }

        holder.txt.setText(data.get(position).getName());
        //holder.pk.setMaxValue(20);
        //holder.pk.setMinValue(0);

        return vi;
    }

    private class ViewHolder
    {
        TextView txt;
        Button add;
        Button sub;
        TextView num;
        //NumberPicker pk;
    }

}

When I try debugging to see what's going on, counter doesn't even initialize with '0'.

I tried initializing the counter in the getView() method, however in order to do so I need to set the counter to final, and then another error shows up saying

The final local variable counter cannot be assigned, since it is defined in an enclosing type.

Any suggestions?

Updated for additional code:

public class Material extends Activity 
    {
    ArrayList<String> materialList;
    ListView lv;
    Button btnConfirm;

    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_material);

        lv = (ListView)findViewById(R.id.list);
        btnConfirm = (Button)findViewById(R.id.btnConfirm);

        materialList = new ArrayList<String>();
        Intent i = getIntent();

        materialList = i.getStringArrayListExtra("materialList");

        if(materialList != null)
        {
            Toast t = Toast.makeText(getApplicationContext(), materialList.get(0).toString(), Toast.LENGTH_LONG);
            t.show();
        }
        else
        {
            //FILL HERE LATER
        }

        ArrayList<MaterialClass> materials = new ArrayList<MaterialClass>();
        for(String temp : materialList)
        {
            MaterialClass m = new MaterialClass();
            m.setName(temp);
            materials.add(m);
        }

        MaterialListViewAdapter adapter = new MaterialListViewAdapter(getApplicationContext(), R.layout.materialdialogcontent, materials);
        lv.setAdapter(adapter);
    }

}

Answer 1

You should implement the onItemClickListener for your listView . You are using listener in adapter class but practically those numbers are nothing but items of that listView, so that to operate on those buttons (listView's items) you've not defined onItemClickListener. So after setting adapter write

lv.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> listView, View item, int position, long id) {

         // here you are getting position of clicked item
        }      
}

UPDATE:

I've gone through your code again and I found these:

1.you are writing this line:

MaterialListViewAdapter adapter = new MaterialListViewAdapter(getApplicationContext(), R.layout.materialdialogcontent, materials);

but I didn't see any constructor in your Adapter.

2.As you are extending BaseAdapter, you must override getCount() , getItem(int position) and getItemId(int position) method as like getView() . There you are getting issue.

Answer 2

Try this :

public class MaterialListViewAdapter extends BaseAdapter 
{
    ViewHolder holder;
    int counter = 0;

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

        View vi = convertView;

        //ViewHolder holder = new ViewHolder();

        if(vi == null)
        {
            holder = new ViewHolder();

            vi = inflater.inflate(R.layout.materialdialogcontent, null);

            //Initialize Buttons and TextViews.
            //holder.pk = (NumberPicker)vi.findViewById(R.id.npMaterialAmount);

            vi.setTag(holder);
        }
        else
        {
            holder = (ViewHolder)vi.getTag();
        }

        holder.txt.setText(data.get(position).getName());
        //holder.pk.setMaxValue(20);
        //holder.pk.setMinValue(0);

        holder.add.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v) 
            {
                counter++;
                holder.num.setText("" + counter);
            }
        });

        holder.sub.setOnClickListener(new View.OnClickListener()
        {   
            @Override
            public void onClick(View v) 
            {
                counter--;
                holder.num.setText("" + counter);
            }
        });

        return vi;
    }

    private class ViewHolder
    {
        TextView txt;
        Button add;
        Button sub;
        TextView num;
        //NumberPicker pk;
    }

}