How can i fix my null pointer exception

Question

I\'ve been trying to fix this null pointer exception but I cant. I know its pointing to a null object but I don\'t how to fix it. I am beginner in Java programming so please don

Answer 1

Your itemsAdapter is never initialized. And it has no values at all. That's why you're getting a NullPointerException when you call your add().

Try to do this:

ArrayList<String> data = new ArrayList<>();

// add some data to your ArrayList.

itemsAdapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, data);

You can also use a String[] array instead of an ArrayList<String> or any other List<String> for that matter.

---

On your code it should look like:

private ArrayAdapter<String> itemsAdapter;
private ArrayList<String> data;

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

    //EditText
    final EditText etTask = (EditText) findViewById(R.id.editText);
    final String task = etTask.getText().toString();

    data = new ArrayList<>();

    itemsAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, data);

    //Button
    Button btn = (Button) findViewById(R.id.button);



    //OnClickListeners
    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            data.add(task);
            itemsAdapter.notifyDataSetChanged();
            etTask.setText("");

        }
    });

---

Edit: If you're creating that ArrayAdapter to use in something like a ListView. Where is it on your code? I guess you also forgot to get it.

Something like:

ListView lv = (ListView) findViewById(R.id.yourListView);
// initialize the adapter and stuff.
lv.setAdapter(itemsAdapter);

For further reading on ListView and adapters, take a look at this link, and this tutorial. Also, check the docs.

Answer 2

I think you should try this..!

ArrayList<MyClass> myList = new ArrayList<MyClass>();
   ArrayAdapter<MyClass> adapter = new ArrayAdapter<MyClass>(this, R.layout.row,
    to, myList.);
listView.setAdapter(adapter);

Answer 3

Initialize your adapter itemsAdapter=new ArrayAdapter<>(...);

Answer 4

Initialize your adapter in OnCreateView() and before adding any value,

itemsAdapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_1, taskNames);

here taskNames can an array or arrayList of task names which you would have defined as,

    ArrayList<String> taskNames; // or String[] taskNames;

Let me know if it works for you...

And do mark it as answer so that it would be useful to others...

Answer 5

You haven't created an instance of an ArrayAdapter for your itemsAdapter variable when you try to call the add() method on it.

Try to initialise it using:

itemsAdapter = new ArrayAdapter<String>(this,
    android.R.layout.simple_list_item_1, values);

Note: values is either a String[] or List<String> so you'll need to pass that in correctly