ComboBox控件设置数据源后默认第一项不显示,该怎么处理

        public DataGridSample()
        {
            InitializeComponent();
            List<Food> foods = new List<Food>
            {
                new Food(1,"Bagel With Cream Cheese"),
                new Food(2,"Deli Sandwich"),
                new Food(3,"Cheeseburger"),
                new Food(4,"Root Beer"),
                new Food(5,"Chocolate Ice Cream")
            };
            comboBox1.DisplayMemberPath = "Name";
            comboBox1.ItemsSource = foods;          
        }