How to add empty arraylist to a ListView? Attempt to invoke interface method 'int java.util.List.size()' on a null object reference

Question

@Override
protected void onCreate(Bundle savedInstanceState) {    
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    NoteTaking_Activity noteTaking_activity = new NoteTaking_Activity();

    arrayList = noteTaking_activity.getHeadlineArray();

    ListView listView = (ListView) findViewById(R.id.List_Of_notes);
    ArrayAdapter<String> adapter = new ArrayAdapter<String>( this, android.R.layout.simple_list_item_1, arrayList );

    listView.setAdapter( adapter );

Executing the code shown above results in the error message

Attempt to invoke interface method 'int java.util.List.size()' on a null object reference.

The array list is empty at first, but then users may fill it.

What can I do to resolve this error?

Can you show us your `getHeadlineArray()` function? I bet that's returning `null` instead of an ArrayList. — Michael Dodd, Sep 26 '18 at 12:49
getHeadlineArray() is simply a getter for my an arraylist (the headline array) — Hossein, Sep 26 '18 at 13:01

Sunny · Answer 1 · 2018-09-26T13:18:37.767

0

Here is the code:

    @Override
    protected void onCreate(Bundle savedInstanceState) {    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        NoteTaking_Activity noteTaking_activity = new NoteTaking_Activity();

        arrayList = noteTaking_activity.getHeadlineArray();

        ListView listView = (ListView) findViewById(R.id.List_Of_notes);
if(arrayList!=null){
        ArrayAdapter<String> adapter = new ArrayAdapter<String>( this, android.R.layout.simple_list_item_1, arrayList );

        listView.setAdapter( adapter );
}

edited Sep 26 '18 at 13:18

answered Sep 26 '18 at 12:52

Sunny

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Would work if OP was using a custom adapter, but a default [`ArrayAdapter`](https://developer.android.com/reference/android/widget/ArrayAdapter) is being used in this case. – Michael Dodd Sep 26 '18 at 12:53
if its' default adapter then you can add `arrayList!=null` and show the error message `No data found`. – Sunny Sep 26 '18 at 13:01
when I do that, the app will no more crash, but it won't carry out reading other statements in the onCreate method. – Hossein Sep 26 '18 at 13:07
I have updated the answer, check it. – Sunny Sep 26 '18 at 13:19
@Hossein If it resolves your issue can you please accept the answer... – Sunny Sep 26 '18 at 13:25

How to add empty arraylist to a ListView? Attempt to invoke interface method 'int java.util.List.size()' on a null object reference

1 Answers1