How do I use an array of objects with the Android ArrayAdapter?

Question

I need to use an ArrayAdapter to populate a ListView in my Android application. In order to use the ArrayAdapter, it says

For example, if you have an array of strings you want to display in a ListView, initialize a new ArrayAdapter using a constructor to specify the layout for each string and the string array:

ArrayAdapter adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, myStringArray);

The arguments for this constructor are:

Your app Context

The layout that contains a TextView for each string in the array

The string array

Then simply call setAdapter() on your ListView:

ListView listView = (ListView) findViewById(R.id.listview); listView.setAdapter(adapter);

However, I do not have an array of strings, I have an array of objects that contain string values.

public class Headers {
    private String from;
    private String to;
    private String subject;

    public Headers (String from, String to, String subject){
        this.from = from;
        this.to = to;
        this.subject = subject;
    }

    public String getFrom() { return from; }
    public void setFrom(String from) { this.from = from; }

    public String getTo() { return to; }
    public void setTo(String to) { this.to = to; }

    public String getSubject() { return subject; }
    public void setSubject(String subject) { this.subject = subject; }
}

My layout does contain a TextView corresponding to values in my object.

Here is my layout with my ListView:

<LinearLayout android:orientation="vertical">
    <ListView android:id="@+id/listOfHeaders" >
</LinearLayout>

And here is the layout for each row in the ListView to be populated by the ArrayAdapter:

<LinearLayout android:orientation="horizontal">
    <TextView android:id="@+id/toTextView" />
    <TextView android:id="@+id/fromTextView" />
    <TextView android:id="@+id/subjectTextView" />
</LinearLayout>

so use ArrayAdapter<Headers>, and not ArrayAdapter<String> — pskink
Yes, but then I need to populate my TextViews with the strings from the Headers object, and it looks like ListView wants an array of Strings. — Brian
not really, you can override getView method and do all the mappings (it is easier if you use ArrayAdapter(Context context, int resource, int textViewResourceId) ctor) — pskink
I have no idea how to implement the intricacies of that. Which is why I posted to StackOverflow. — Brian
just override getView, call super and see what super returns, then 3 simple findViewById should be enough — pskink

Benjamín Molina Benjamín Molina · Accepted Answer · 2016-04-12T18:16:20

Using the ArrayAdapter is not enough, you will need to extend ArrayAdapter and create a custom adapter, so you can overwrite the rows creation to use your list layout. Please check this example:

public class CustomAdapter extends ArrayAdapter<Headers> {

    Context context;
    int layoutResourceId;
    ArrayList<Headers> data = null;

    public CustomAdapter(Context context, int resource, List<Headers> objects) {
        super(context, resource, objects);
        this.layoutResourceId = resource;
        this.context = context;
        this.data = (ArrayList) objects;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View row = convertView;
        HeaderHolder holder = null;

        if(row == null)
        {
            LayoutInflater inflater = ((Activity)context).getLayoutInflater();
            row = inflater.inflate(layoutResourceId, parent, false);

            holder = new HeaderHolder();
            holder.from = (TextView) row.findViewById(R.id.fromTextView);
            holder.to = (TextView)row.findViewById(R.id.toTextView);
            holder.subject = (TextView)row.findViewById(R.id.subjectTextView);

            row.setTag(holder);
        }
        else
        {
            holder = (HeaderHolder) row.getTag();
        }

        Headers item = data.get(position);
        holder.from.setText(item.getFrom());
        holder.to.setText(item.getTo());
        holder.subject.setText(item.getSubject());

        return row;
    }

    private class HeaderHolder {
        public TextView from;
        public TextView to;
        public TextView subject;

    }
}

For the Activity, on the onCreate method:

ListView list = (ListView) findViewById(R.id.listView);
ArrayList<Headers> data = new ArrayList<Headers>();
data.add(new Headers("from", "to", "subject"));

ArrayAdapter adapter = new CustomAdapter(this, R.layout.list, data);
list.setAdapter(adapter);

You can see that the CustomAdapter is using HeaderHolder as part of the ViewHolder pattern so the list management is efficient.

How do I use an array of objects with the Android ArrayAdapter?

2 Answers