RecyclerView Demo

This is a simple contacts app to demonstrate how to display a list of objects using a RecyclerView.

Contact Model

Ask students to copy the following Contact model:

public class Contact {
    private String mName;
    private boolean mOnline;

    public Contact(String name, boolean online) {
        mName = name;
        mOnline = online;
    }

    public String getName() {
        return mName;
    }

    public boolean isOnline() {
        return mOnline;
    }

    private static int lastContactId = 0;

    public static List<Contact> createContactsList(int numContacts) {
        List<Contact> contacts = new ArrayList<>();

        for (int i = 1; i <= numContacts; i++) {
            contacts.add(new Contact("Person " + ++lastContactId, i <= numContacts / 2));
        }

        return contacts;
    }
}

Key Demonstration Points

Recycled items

Without re-enabling the button on each call to onBindViewHolder, the button will retain the state from the last contact that was displayed in its ViewHolder.

This can be demonstrated by scrolling to the bottom of the list and back up. Enabled buttons at the top of the list will now be disabled.

    // In Contact.java

    @Override
    public void onBindViewHolder(ViewHolder viewHolder, int position) {
        Contact contact = mContacts.get(position);

        TextView textView = viewHolder.nameTextView;
        textView.setText(contact.getName());

        Button button = viewHolder.messageButton;

        if (contact.isOnline()) {
            button.setText("Message");

            // OMIT to show that rows are recycled.
            //
            // Scrolling past the midpoint of the list (when contacts are listed as offline)
            // and scrolling back up should result in some buttons being inadvertently disabled.
            button.setEnabled(true);
        }
        else {
            button.setText("Offline");
            button.setEnabled(false);
        }
    }

Notifying the adapter that the UI must be updated due to dataset changes

Without the call to notifyItemRangeInserted, the UI will not reflect the additional contacts that have been appended to the contact list.

    // In Contact.java

    public void addMoreContacts(List<Contact> newContacts) {
        int insertionPosition = mContacts.size();
        mContacts.addAll(newContacts);

        // OMIT to illustrate how the UI is independent from the dataset
        // and does not update automatically.
        notifyItemRangeInserted(insertionPosition, newContacts.size());
    }