在用户控件的下拉列表中设置选定的索引 [英] Set selected index in a Dropdownlist in usercontrol

问题描述

我对用户控件还很陌生.到目前为止，我发现它们对于处理大量重复的用户输入字段非常有用.但是，我在预填充控件中的下拉列表时遇到了问题.我将一个ddl添加到我的ascx页面，然后绑定该ddl并将其公开:

I'm fairly new to usercontrols. So far, I've found them quite useful for handling large amounts of repeating user input fields. However, I'm having a problem with prepopulating a dropdownlist in the control. I add a ddl to my ascx page then I bind the ddl and expose it:

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        List<Travel_CarSize> tc = Travel_CarSizes.GetCarSizes();
        ddlCarSize.DataSource = tc;
        ddlCarSize.DataTextField = "CarSize";
        ddlCarSize.DataValueField = "CarSizeID";
        ddlCarSize.DataBind();
    }
}

public string CarSize
{
    get { return ddlCarSize.SelectedValue.ToString(); }
    set { ddlCarSize.SelectedIndex = ddlCarSize.Items.IndexOf(ddlCarSize.Items.FindByValue(value)); }
}

但是，当我以编程方式尝试在控件中设置ddl的选择时，我总是最终将其设置为THEN并将其绑定.在我的aspx.cs文件中设置:

However, when I programatically try to set a selection for the ddl in the control I always end up setting it THEN binding it. In my aspx.cs file I set:

CarControl1.CarSize = "3";

该程序旨在显示一个空的用户控件(带有数据绑定的ddl)和一个gridview.用户选择一个gridview条目，并且该用户控件被数据填充.因此，ddl从一开始就受到约束，然后发生了导致预选" ddl的事件.

The program is designed to display an empty usercontrol (with a databound ddl) and a gridview. The user selects a gridview entry and that usercontrol gets filled with the data. So the ddl gets bound from the start then the events happen that lead to the "pre-selected" ddl.

当这没有给我结果时，我在if(！IsPostBack)，ddlCarSize.DataBind();上设置了一个断点.和集合{}.我运行该程序，它将绑定我的ddl，然后在gridview中进行选择.当我单击选择时，我发现它在用户控件中击中了if(！IsPostBack)并说:哦，这是一个回发，请不要输入if."然后它命中了set {}，但ddl现在为空.然后它再次击中了if(！IsPostBack)，由于某种原因，现在它说它不是回发并重新绑定了ddl.

When this didn't give me the result I was looking for I put a breakpoint on the if(!IsPostBack), the ddlCarSize.DataBind(); and the set{}. I run the program, it binds my ddl and I make a selection in the gridview. When I click the select I found that it hits the if(!IsPostBack) in the usercontrol and says "Oh, this is a postback, don't go in the if." then it hits the set{} but the ddl is empty now. Then it hits the if(!IsPostBack) again and for some reason now says it's not a postback and rebinds the ddl.

我认为这是一个非常普遍的问题，但我尚未找到解决方案.任何帮助将不胜感激.

I figure this is a pretty common problem but I've yet to find a solution. Any help would be greatly appreciated.

推荐答案

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        Bind()
    }
}

public Bind()
{
    if (ddlCarSize.Items.Count == 0)
    {
        List<Travel_CarSize> tc = Travel_CarSizes.GetCarSizes();
        ddlCarSize.DataSource = tc;
        ddlCarSize.DataTextField = "CarSize";
        ddlCarSize.DataValueField = "CarSizeID";
        ddlCarSize.DataBind();
    }
}

public string CarSize
{
    get { return ddlCarSize.SelectedValue.ToString(); }
    set 
    {
        Bind();
        ddlCarSize.SelectedIndex = ddlCarSize.Items.IndexOf(ddlCarSize.Items.FindByValue(value)); }
}

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