Custom ListView Not Displaying in Emulator - Black Activity

Question

FI am trying to display a custom ListView using a custom adapter for a Car class. However, when I run the app in the emulator, the activity screen is black. I added some static text to the XML layout to debug, and the text appeared, so the issue seems to be with the ListView or setAdapter().

Here’s my setup:

XML Layout (activity_main.xml):

`

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



    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/cars_list"/>

</LinearLayout>

`

This is my main activity:

package com.example.carscustomadapter;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ListView carsList = findViewById(R.id.cars_list);

        List<Car> cars = new ArrayList<>();

        cars.add(new Car(1000,20,2));
        cars.add(new Car(1000,40,2));
        cars.add(new Car(1000,60,8));
        cars.add(new Car(1000,100,5));
        cars.add(new Car(1000,20,2));
        cars.add(new Car(1000,40,2));
        cars.add(new Car(1000,60,8));
        cars.add(new Car(1000,100,5));
        cars.add(new Car(1000,20,2));
        cars.add(new Car(1000,40,2));
        cars.add(new Car(1000,60,8));
        cars.add(new Car(1000,100,5));
        cars.add(new Car(1000,20,2));
        cars.add(new Car(1000,40,2));
        cars.add(new Car(1000,60,8));
        cars.add(new Car(1000,100,5));

        CarsAdapter carsAdapter = new CarsAdapter(cars);
        carsList.setAdapter(carsAdapter);


    }
}

Custom Adapter (CarsAdapter)

 public class CarsAdapter extends BaseAdapter implements View.OnClickListener {

    private List<Car> cars;

    public CarsAdapter(List<Car> cars) {
        this.cars = cars;
    }


    @Override
    public int getCount() {
        return 0;
    }

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

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        if (view == null)
            view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.car_layout, viewGroup, false);

        TextView kmTv = view.findViewById(R.id.km_tv);
        TextView fuelTv = view.findViewById(R.id.fuel_tv);

        Button driveBtn = view.findViewById(R.id.drive_btn);
        driveBtn.setTag(i);

        Car car = cars.get(i);

        kmTv.setText(car.getMileage() + "");
        fuelTv.setText(car.getFuel() + "");

        driveBtn.setOnClickListener(this);

        return view;
    }

    @Override
    public void onClick(View v) {
        LinearLayout root = (LinearLayout) v.getParent();
        EditText editText = root.findViewById(R.id.km_et);
        Car car = cars.get((Integer) v.getTag());
        car.drive(Integer.parseInt(editText.getText().toString()));
        notifyDataSetChanged();

    }
}

The Issue:: When running the app, the screen is black, and the ListView does not display anything. I suspect the issue might be with:

1.The adapter configuration or implementation. 2.Incorrect data being provided to the ListView. 3.Layout issues with the car_layout.xml (not provided here but could be relevant).

screen Image

What I Tried: 1.Adding static text to the activity_main.xml to confirm the layout is 2.rendering properly. 3.Verifying that setAdapter() is called. 4.Debugging the app, but I’m not sure where the problem lies.

What I Expect I expect to see a ListView populated with rows of Car objects. Each row should display the mileage and fuel, with a button for actions.

Answer 1

In you CarsAdapter you are returning 0 from the getCount() method. The adapter uses this to know how many items to draw in the ListView. It should return the count of the items in the cars list