/**
 * The Model. Model stores items and notifies
 * observers about changes.
 */
function ListModel(items) {
    this._items = items;
    this._selectedIndex = -1;

    this.itemAdded = new Event(this);
    this.itemRemoved = new Event(this);
    this.selectedIndexChanged = new Event(this);
}

ListModel.prototype = {
    getItems : function () {
        return [].concat(this._items);
    },

    addItem : function (item) {
        this._items.push(item);
        this.itemAdded.notify({ item : item });
    },

    removeItemAt : function (index) {
        var item;

        item = this._items[index];
        this._items.splice(index, 1);
        this.itemRemoved.notify({ item : item });
        if (index === this._selectedIndex) {
            this.setSelectedIndex(-1);
        }
    },

    getSelectedIndex : function () {
        return