Radio button 代码隐藏获取错误的单选按钮值

就像我在标题中写的那样，当我试图更改单选按钮的选择时，隐藏的代码得到了错误的值

困境。aspx:

<asp:RadioButtonList ID="rbList" runat="server">
    <asp:ListItem Text="Yes, please." />
    <asp:ListItem Text="No, thanks." />
    <asp:ListItem Text="Ummm... maybe." />
</asp:RadioButtonList>
<asp:Button ID=""btnChoose" runat="server" text="OK" OnClick="btnChoose_Click" />

protected void Page_Load(object sender, EventArgs e)
{
    int initialIndex = GetInitialIndex(); // Simplified for sake of question.
    rbList.SelectedIndex = initialIndex; // This works.
}

protected void btnChoose_Click(object sender, EventArgs e)
{
    int selection = rbList.SelectedIndex; // This gets it wrong!
}

隐藏代码没有获取新选择的单选按钮，而是认为所选索引是初始索引

为什么?

有人发布了此答案，但出于某种原因将其删除。
不管是谁在我面前发布了这个答案——它是有效的

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        int initialIndex = GetInitialIndex(); // Simplified for sake of question.
        rbList.SelectedIndex = initialIndex; // This works.
    }
}