DropDownList有一种奇怪的行为

Question

aspx：

<asp:DropDownList runat="server" ID="ddlTimeZone" DataSource ="<%# TimeZoneInfo.GetSystemTimeZones().ToDictionary(z => z.DisplayName)%>" DataTextField="Key" DataValueField="Value">`

html：

<select name="ctl00$MainContent$ddlTimeZone" id="MainContent_ddlTimeZone">
<option value="(UTC-12:00) International Date Line West">(UTC-12:00) International Date Line West</option>
<option value="(UTC-11:00) Midway Island, Samoa">(UTC-11:00) Midway Island, Samoa</option>
<option value="(UTC-10:00) Hawaii">(UTC-10:00) Hawaii</option>
<option value="(UTC-09:00) Alaska">(UTC-09:00) Alaska</option>
<option value="(UTC-08:00) Pacific Time (US &amp; Canada)">(UTC-08:00) Pacific Time (US &amp; Canada)</option>
<option value="(UTC-08:00) Tijuana, Baja California">(UTC-08:00) Tijuana, Baja California</option>
<option value="(UTC-07:00) Arizona">(UTC-07:00) Arizona</option>
<option value="(UTC-07:00) Chihuahua, La Paz, Mazatlan">(UTC-07:00) Chihuahua, La Paz, Mazatlan</option>

当我试图获得ddlTimeZone.SelectedValue时，我总是得到null (或-1，我不记得了)，而SelectedItem总是等于null。

Answer 1

我已经蹲下了。一直以来

protected void Page_Load(object sender, EventArgs e)
    {

        if (!IsPostBack)
            DataBind();
    }