Why does my app crash in both emulator and phone?

Question

Why does my app keep crashing in both emulator and in OnePlus Nord. Android studio doesnt detect any error with my code.

I wanted my app to show one sentence randomly when I click on the button.

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.lang.String;
import java.lang.StringBuilder;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Random;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    ArrayList<String> SList;
    TextView Sentence;

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

        Sentence = (TextView) findViewById(R.id.Sentence);
        Button button = findViewById(R.id.button);

        button.setOnClickListener((View v) -> {
            Sentence.setText(getRandomFromList(SList));
        });
    };

    private ArrayList<String> getSampleList() {
        ArrayList<String> list = new ArrayList();
        list.add("Apple");
        list.add("Banana");
        list.add("Ciku");
        list.add("Danny ate the other fruits.");
        return list;
    }

    private String getRandomFromList(ArrayList<String> list) {
        Random rand = new Random();
        return list.get(rand.nextInt(list.size()));
    }
}

what error do you get? that should explain a bit more – Stultuske Jun 18 '21 at 05:51 — Stultuske, Jun 18 '21 at 05:51
try Sentence.setText(getRandomFromList(getSampleList())); – Eyosiyas Jun 18 '21 at 06:03 — Eyosiyas, Jun 18 '21 at 06:03

Darkman · Answer 1 · 2021-06-18T06:42:38.310

Your ArrayList<String> SList; has not been initialised.

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

    Sentence = (TextView) findViewById(R.id.Sentence);
    Button button = findViewById(R.id.button);

    //Add this one.
    SList = new ArrayList<String>();

    button.setOnClickListener((View v) -> {
        Sentence.setText(getRandomFromList(SList));
    });
}

And this one seems incorrect as well. Did you mean this:

private String getRandomFromList(ArrayList<String> list) {
    Random rand = new Random();
    list = getSampleList();
    return list.get(rand.nextInt(list.size() - 1));
}

Or maybe this one:

private String getRandomFromList(ArrayList<String> list) {
    Random rand = new Random();
    List<String> sampleList = getSampleList();
    list.add(rand.nextInt(sampleList.size() - 1));
    return list.get(rand.nextInt(list.size() - 1));
}

You can also remove the parameter from getRandomFromList, if you're setting it inside the function anyway — Gregor Rant, Jun 18 '21 at 06:37

score 0 · Answer 2 · answered Jun 18 '21 at 06:37

You are declaring SList but want to use getSampleList(). So instead of SList just pass getSimpleList() to your method getRandomFromList()

Simplye replace your class with this:

import androidx.appcompat.app.AppCompatActivity;


import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.lang.String;
import java.lang.StringBuilder;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Random;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    ArrayList<String> SList;
    TextView Sentence;

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


        TextView Sentence;



            Sentence = (TextView) findViewById(R.id.Sentence);
            Button button = findViewById(R.id.button);

            button.setOnClickListener((View v) -> {
                Sentence.setText(getRandomFromList(getSampleList()));


            });

        };

        private ArrayList<String> getSampleList(){
            ArrayList<String> list = new ArrayList();
            list.add("Apple");
            list.add("Banana");
            list.add("Ciku");
            list.add("Danny ate the other fruits.");
            return list;
        }

        private String getRandomFromList(ArrayList<String> list){
            Random rand = new Random();
            return list.get(rand.nextInt(list.size()));
        }


}

And it will work!

Why does my app crash in both emulator and phone?

2 Answers2