双向绑定对象值：@SelectedItem
@code {
private int SelectedItem { get; set; } = 2;
private List Items { get; set; } = new List
{
new SelectedItem{ Text = "北京", Value = "0" },
new SelectedItem{ Text = "上海", Value = "1" },
new SelectedItem{ Text = "广州", Value = "2" },
};
}