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Android Studio – Why Activity closes as it starts?

I have a activity in Android Studio and the app closes whenever I start that activity. Can you please check what’s the problem.

public class AddEx extends AppCompatActivity {

public int max, min;

public int w,m;

public ArrayList<Object>exer = new ArrayList<>();
public ArrayList<Integer>ans = new ArrayList<>();
public ListView ex = findViewById(R.id.Exerciselist);
public ArrayAdapter<Object> arrayAdapter = new ArrayAdapter<>(this, android.R.layout.select_dialog_item, exer);


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

public void start()
{
    for (int i = 0; i<=9; i++)
    {


        Intent intent = getIntent();
        int Token = Integer.parseInt(intent.getStringExtra(Add_Subtract.MSG));

        if(Token == 1)
        {
            max = 9;
            min = 1;
        }
        else if(Token == 2)
        {
            max = 99;
            min = 10;
        }
        else if(Token == 3)
        {
            max = 999;
            min = 100;
        }
        else if(Token == 4)
        {
            max = 9999;
            min = 1000;
        }
        else if(Token == 5)
        {
            max = 99999;
            min = 10000;
        }

        w = ((int) Math.floor(Math.random() * (max - min + 1) + min));
        m = (int)Math.floor(Math.random() * (max - min + 1) + min);
        ans.add(w+m);
        exer.add(w+" + "+m);
    }
    ex.setAdapter(arrayAdapter);
}

public void answers(View view)
{
    for (int i = 0; i<=9; i++)
    {
        Object ques = exer.get(i);
        exer.set(i, ques+" = "+ans.get(i));
    }
    ex.setAdapter(arrayAdapter);
}

}

The function answers is button controlled. I want the start function to run as the activity starts but as soon the activity starts, the app closes. I request you to tell the problem
Thanks

Tags:

2

Answers


  1. 0

    public ListView ex = findViewById(R.id.Exerciselist);

    Remove this line and add it to either onCreate() or start()

    You are initialising Exerciselist even before the layout is initialised, so the app doesn’t know what it is, that’s why it crashes

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  2. 0

    i noted 2 problems:

    1 : you attached by id not in onCreate/Function.

    2: you attached the adapter to an empty array called "exer" – thats why it returns an null Exception.

    public class AddEx extends AppCompatActivity {

public int max, min;

public int w,m;

public ArrayList<Object>exer = new ArrayList<>();
public ArrayList<Integer>ans = new ArrayList<>();
public ListView ex;


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

    // move the list view attach to here

        ex = findViewById(R.id.Exerciselist);
    start();
  }
   public void start()
   {
    for (int i = 0; i<=9; i++)
   {


    Intent intent = getIntent();
    int Token = Integer.parseInt(intent.getStringExtra(Add_Subtract.MSG));

    if(Token == 1)
    {
        max = 9;
        min = 1;
    }
    else if(Token == 2)
    {
        max = 99;
        min = 10;
    }
    else if(Token == 3)
    {
        max = 999;
        min = 100;
    }
    else if(Token == 4)
    {
        max = 9999;
        min = 1000;
    }
    else if(Token == 5)
    {
        max = 99999;
        min = 10000;
    }

    w = ((int) Math.floor(Math.random() * (max - min + 1) + min));
    m = (int)Math.floor(Math.random() * (max - min + 1) + min);
    ans.add(w+m);
    exer.add(w+" + "+m);
}

    // move the array adapter here

      ArrayAdapter<Object> arrayAdapter = new ArrayAdapter<(this,android.R.layout.select_dialog_item, exer);
  ex.setAdapter(arrayAdapter);
 }

    about the code blow – it doesnt clear when do you what it to run’ and by the way you dont even call this function anywhere in the code….

    public void answers(View view)
{
   for (int i = 0; i<=9; i++)
   {
    Object ques = exer.get(i);
    exer.set(i, ques+" = "+ans.get(i));
   }
   ex.setAdapter(arrayAdapter);
  }
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