在OnInit()中获取控件值的最佳方法是什么?

我最近看了 this article on smart use of ViewState 我特别感兴趣的是在viewstate中没有不必要的静态数据。但是,我也很好奇是否可以为父子下拉列表做同样的事情,比如经典的Country/CountrySubdivision示例。

所以我有了这个标记:

    <asp:DropDownList runat="server" ID="ddlCountry" DataTextField="Name" DataValueField="ID" EnableViewState="false" />
    <asp:DropDownList runat="server" ID="ddlCountrySubdivision" DataTextField="Name" DataValueField="ID" EnableViewState="false" />
    <asp:Button runat="server" ID="btnTest" />

这背后的代码是:

    public class Country
    {
        public string Name { get; set;}
        public int Id { get; set; }
    }

    public class CountrySubdivision
    {
        public string Name { get; set; }
        public int Id { get; set; }
        public int CountryId { get; set; }
    }

    protected override void OnInit(EventArgs e)
    {
        var l = new List<Country>();
        l.Add(new Country { Name = "A", Id = 1 });
        l.Add(new Country { Name = "B", Id = 2 });
        l.Add(new Country { Name = "C", Id = 3 });
        ddlCountry.DataSource = l;
        ddlCountry.DataBind();

        var l2 = new List<CountrySubdivision>();
        l2.Add(new CountrySubdivision { Name = "A1", Id = 1, CountryId = 1 }); 
        l2.Add(new CountrySubdivision { Name = "A2", Id = 2, CountryId = 1 });
        l2.Add(new CountrySubdivision { Name = "B1", Id = 4, CountryId = 2 });
        l2.Add(new CountrySubdivision { Name = "B2", Id = 5, CountryId = 2 });
        l2.Add(new CountrySubdivision { Name = "C1", Id = 7, CountryId = 3 });
        l2.Add(new CountrySubdivision { Name = "C2", Id = 8, CountryId = 3 });

        // this does not work: always comes out 1 regardless of what's actually selected
        var selectedCountryId = string.IsNullOrEmpty(ddlCountry.SelectedValue) ? 1 : Int32.Parse(ddlCountry.SelectedValue);

        // this does work: 
        var selectedCountryIdFromFormValues = Request.Form["ddlCountry"];

        ddlCountrySubdivision.DataSource = l2.Where(x => x.CountryId == selectedCountryId).ToList();
        ddlCountrySubdivision.DataBind();

        base.OnInit(e);
    }

所以我注意到的第一件事就是 EnableViewstate 是 false ,我的国家/地区控制的价值在所有请求中都是持久的,不需要额外的努力。太好了。这是很多系列化的东西,我不需要在提交表单时跨线发送。

然后我用一对父子下拉列表来举上面的例子,我看到了 ddlCountry.SelectedValue 违约,而 Request.Form["ddlCountry"] 正在反映控件的值。

有办法保持 EnableViewState = "false" 不诉诸 Request.Form 要获取依赖控件的值?