OnSelectedIndexChanged事件不會觸發DropDownList的第一個元素

我有一個DropDownList和方法OnSelectedIndexChanged事件更改一個標籤的內容。除了DropDownList的第一個元素外，它工作正常。有任何想法嗎？OnSelectedIndexChanged事件不會觸發DropDownList的第一個元素

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Web; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using Newsletter.DAL; 
using Newsletter.Services; 

public partial class Senders : System.Web.UI.Page 
{ 
    private SenderService _client; 
    private List<Sender> _allSenders; 
    private DropDownList _dropDownListSenders; 
    private TextBox _emailBox; 
    private string _selectedSender; 

    protected void Page_Load(object sender, EventArgs e) 
    { 
     _client = new SenderService(); 
     _allSenders = _client.GetAllSenders(); 
     _dropDownListSenders = (DropDownList)loginViewMain.FindControl("DropDownListSenders"); 
     _emailBox = (TextBox)loginViewMain.FindControl("textBoxEmail"); 
    } 

protected void DropDownListSenders_SelectedIndexChanged(object sender, EventArgs e) 
    { 
     _selectedSender = _dropDownListSenders.SelectedValue; 
     _emailBox.Text = _selectedSender; 
    } 
}

來源

2013-01-19 pmichna

嘗試在DDL上將「AutoPostback」設置爲true。 – keyboardP

看到http://stackoverflow.com/questions/8699163/first-item-in-dropdownlist-doesnt-fire-selectedindexchanged-at-all –