下拉列表未在部分回发中填充 [英] Drop Down List not getting populated on partial post back

问题描述

我正在尝试在部分回发中填充一个下拉列表，不确定为什么它不起作用.

I am trying to populate a drop down list on partial post back, not sure why it's not working.

这有效，

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

这不起作用

protected void Page_Load(object sender, EventArgs e)
            {
                if (IsPostBack)
                {
                     populatemyDropDownList();
                }

场景

* 我单击UpdatePanel_1中的button_1，然后触发部分回发(不刷新页面)，并尝试填充UpdatePanel_2 *中的DropDownList

当我调试时，我可以看到方法背后的代码正在触发并经历此代码，但没有任何收益，我认为部分回发会重置DropDownList吗????

when I debug, I can see code behind method is triggering and going through this code but no gain, I think partial post back resets DropDownList ????

using (SqlDataSource sqlds = new SqlDataSource(ConnectionString(), SelectCommand()))
            {
                drop1.DataSource = sqlds;
                drop1.DataTextField = "UserName";
                drop1.DataBind();
            }

推荐答案

您可以使用

ScriptManager.GetCurrent(Page).IsInAsyncPostBack

检查您是否处于异步回发中.

to check if you're in an asynchronous postback.

但是，我不会将您的逻辑依赖于回发(或!IsPostBack)和IsInAsyncPostBack.相反，我会使用正确的事件.在这种情况下，您要处理button_1的click事件以将DropDownList填充到UpdatePanel2中.

However, i would not rely your logic on postbacks(or !IsPostBack) and IsInAsyncPostBack. Instead i would use the correct events. In this case you want to handle button_1's click event to fill the DropDownList in UpdatePanel2.

请注意，您应该将UpdatePanel2的UpdateMode设置为Conditional.然后，您可以在填写DropDownList后手动调用UpdatePanel2.Update().

Note that you should make UpdatePanel2's UpdateMode Conditional. Then you can call UpdatePanel2.Update() manually after you've filled the DropDownList.

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