ArrayAdapter Cannot resolve constructor

Question

I am getting this error in the oncreate method. It seems to be related to the List i created beforehand. Could you give any suggestions what the activity could be or how i can find that out?

public class MainActivity extends AppCompatActivity {

    private List<ListItem> items;
    private ArrayAdapter<String> adapter;
    private ListView listView;

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

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });


        items.add(new ListItem("test", "https://google.com"));  

        listView = (ListView) findViewById(R.id.listView);

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

        listView.setAdapter(adapter);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }


}

public class ListItem {

    private long id;
    private String url;
    private String title;

    public ListItem(String title, String url) {
        this.title = title;
        this.url = url;
    }

    public String getUrl() {
        return url;
    }

    @Override
    public String toString() {
        return title;
    }
}

If i change the private list to String instead of ListItem it does work, any suggestions on why or how?

items is never initialized here. This will give you NPE.

Mohammedsalim Shivani
– Mohammedsalim Shivani

2018-04-02 06:17:58 +00:00
Commented Apr 2, 2018 at 6:17 — Mohammedsalim Shivani
– Mohammedsalim Shivani, Commented Apr 2, 2018 at 6:17

Rohit5k2 · Accepted Answer · 2016-02-12 18:17:57Z

0

You are telling the ArrayAdapter that you will be using a String but you are passing ListItem in parameters.

Change

adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, items);

to

adapter = new ArrayAdapter<ListItem>(getActivity(), android.R.layout.simple_list_item_1, items);

and

private ArrayAdapter<String> adapter;

to

private ArrayAdapter<ListItem> adapter;

edited Feb 12, 2016 at 18:17

answered Feb 12, 2016 at 18:05

Rohit5k2

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4 Comments

patrick Over a year ago

excuse me a small typo i did use adapter = new ArrayAdapter<String>(this, ...) before. I have changed it according to you but still get an error: required java.lang.string and found studentportal.ListItem. I tried putting private ArrayAdapter<String> adapter; to private ArrayAdapter<ListItem> adapter; however i get a NullPointerException then

Rohit5k2 Over a year ago

At every place you should have ArrayAdapter<ListItem>. Don't use String anywhere. Also you should have List<ListItem>

patrick Over a year ago

I did that exactly but then i get "Unable to start activity ComponentInfo" with a "java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add"

Rohit5k2 Over a year ago

Change private List<ListItem> items = new ArrayList<ListItem>();. You need to initialize it before adding item to the list.

Mohammedsalim Shivani · Accepted Answer · 2018-04-02 06:20:31Z

0

Just add following line in your code.

item = new ArrayList<ListItem>;

Just above the following line.

items.add(new ListItem("test", "https://google.com"));

answered Apr 2, 2018 at 6:20

Mohammedsalim Shivani

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