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

问题描述

我正在创建一个服务器控件，它基本上绑定了两个下拉列表，一个用于国家/地区，一个用于州，并在国家/地区的 selectedindexchanged 事件上更新州下拉列表.但是，它不会回传.任何想法为什么?将它们包装在 UpdatePanel 中的奖励积分(有渲染问题；可能是因为我没有要引用的页面?)

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?)

这是我所拥有的(删除了一些额外的数据访问内容):

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();
    }
}

页面上有视图状态，页面上的其他控件正确执行回发，但不是这个.

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

推荐答案

Viewstate 是否开启?

Is Viewstate turned on?

也许你应该重新考虑覆盖渲染功能

Perhaps you should reconsider overriding the rendering function

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

而是将下拉列表添加到控件并使用默认的 RenderContents 呈现控件.

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

请参阅我在之前的评论中提到的 Dennis 的回答:

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

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

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