ASP.NET / C＃：DropDownList中的SelectedIndexChanged在服务器控件不触发 [英] ASP.NET / C#: DropDownList SelectedIndexChanged in server control not firing

问题描述

我创建基本上结合两个下拉列表，一个国家，一个国家，并更新该国的SelectedIndexChanged事件的状态下拉列表中选择服务器控件。但是，它不回发。任何想法，为什么？在一个UpdatePanel包裹它们（有呈现问题？;也许是因为我没有一个页面引用）奖励积分

I'm creating a server control that basically binds two dropdown lists, one for country and one for state, and updates the state dropdown on the country's selectedindexchanged event. However, it's not posting back. Any ideas why? Bonus points for wrapping them in an UpdatePanel (having rendering issues; maybe because I don't have a Page to reference?)

下面是我有（有一些额外的数据访问东西剥离出来）：

Here's what I have (with some extra data access stuff stripped out):

public class StateProv : WebControl
{
    public string SelectedCountry;
    public string SelectedState;

    private DropDownList ddlCountries = new DropDownList();
    private DropDownList ddlStates = new DropDownList();

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        IList<Country> countries = GetCountryList();
        IList<State> states = new List<State>();

        if (SelectedCountry != null && SelectedCountry != "")
        {
            states = GetStateList(GetCountryByShortName(SelectedCountry).CountryShortName);
        }
        else
        {
            states.Add(new State { CountryId = 0, Id = 0, StateLabelName = "No states available", StateLongName = "No states available", StateShortName = "" });
        }

        ddlCountries.DataSource = countries;
        ddlCountries.DataTextField = "CountryLongName";
        ddlCountries.DataValueField = "CountryShortName";
        ddlCountries.SelectedIndexChanged += new EventHandler(ddlCountry_SelectedIndexChanged);
        ddlCountries.AutoPostBack = true;

        ddlStates.DataSource = states;
        ddlStates.DataTextField = "StateLongName";
        ddlStates.DataTextField = "StateShortName";

        ddlCountries.DataBind();
        ddlStates.DataBind();

        if (!string.IsNullOrEmpty(SelectedCountry))
        {
            ddlCountries.SelectedValue = SelectedCountry;

            if (!string.IsNullOrEmpty(SelectedState))
            {
                ddlStates.SelectedValue = SelectedState;
            }
        }            
    }


    protected override void RenderContents(HtmlTextWriter output)
    {
        ddlCountries.RenderControl(output);
        ddlStates.RenderControl(output);
    }

    private IList<Country> GetCountryList()
    {
        //return stuff
    }

    private IList<State> GetStateList(Country country)
    {
        //return stuff
    }

    private IList<State> GetStateList(string countryAbbrev)
    {
        Country country = GetCountryByShortName(countryAbbrev);
        return GetStateList(country);
    }

    private Country GetCountryByShortName(string countryAbbrev)
    {
        IList<Country> list = dataAccess.RetrieveQuery<Country>();
        //return stuff
    }

    private IList<State> GetAllStates()
    {
        //return stuff
    }

    protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)
    {
        IList<State> states = GetStateList(GetCountryList()[((DropDownList)sender).SelectedIndex]);
        ddlStates.DataSource = states;
        ddlStates.DataBind();
    }
}

编辑：视图状态在页面上，页面上的其他控件正确执行回发，只是没有这种

Viewstate is on the page, and other controls on the page perform postbacks correctly, just not this.

推荐答案

时的视图状态打开了吗？

Is Viewstate turned on?

编辑：
也许你应该重新考虑重写渲染功能

Perhaps you should reconsider overriding the rendering function

  protected override void RenderContents(HtmlTextWriter output)
    {
        ddlCountries.RenderControl(output);
        ddlStates.RenderControl(output);
    }

和替代dropdownlists添加到控件并使用默认RenderContents呈现控件。

and instead add the dropdownlists to the control and render the control using the default RenderContents.

编辑：
看到丹尼斯我在previous评论暗示了答案：

See the answer from Dennis which I alluded to in my previous comment:

Controls.Add ( ddlCountries );
Controls.Add ( ddlStates );

这篇关于ASP.NET / C＃：DropDownList中的SelectedIndexChanged在服务器控件不触发的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！