我有一个下拉列表被设置在一个单独的函数。所以，首先当页面加载它会从SQL数据库中获取一个值，并将该值传递给填充下拉列表的方法。根据收到的参数，填充方法将项目插入到下拉列表中。Asp.net下拉列表问题

另外我有代码在页面加载事件像下面

if (!IsPostBack) 
{ 
    // CALL THE POPULATE FUNCTION 
}

上述块将仅填充下拉列表中第一次页面加载的块。我不希望它从一个按钮的邮政backs重新填充

有一个搜索按钮，我必须把一个ID和点击搜索。当我点击搜索时，下拉菜单会保留它的项目，但它会选择第一项。在我点击搜索之前，有时我会更改下拉选择，并且我希望它在点击搜索后保持这种状态，但它总是会返回到第一项。

基本上我有如下：

<html xmlns="http://www.w3.org/1999/xhtml"> 
<head runat="server"> 
    <title></title> 
</head> 
<body> 
    <form id="form1" runat="server"> 
    <div> 

     <asp:DropDownList ID="DropDownList1" runat="server"> 
     </asp:DropDownList> 
     <br /> 
     <br /> 
     <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> 
     <asp:Button ID="Button1" runat="server" Text="Search" /> 
    </div> 
    </form> 
</body> 
</html>

后面的代码：

protected void Page_Load(object sender, EventArgs e) 
{ 
    if(!IsPostBack) 
    { 
     DropDownList1.Items.Clear(); 
     string test = "17/FO"; 
     Populate(test); 
    } 
} 

protected void Populate(string t) 
{ 
    string t1, t2, t3, t4, t5, t6, t7, t8, t9, t10,t11,t12; 
    if (t.Contains("/FI")) 
    { 
     t1 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/FI"; 
     t2 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/SE"; 
     t3 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/TH"; 
     t4 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/FO"; 
     t5 = t.Substring(0, 2) + "/FI"; 
     t6 = t.Substring(0, 2) + "/SE"; 
     t7 = t.Substring(0, 2) + "/TH"; 
     t8 = t.Substring(0, 2) + "/FO"; 
     t9 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/FI"; 
     t10 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/SE"; 
     t11 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/TH"; 
     t12 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/FO"; 
     DropDownList1.Items.Insert(0, new ListItem(t1, "")); 
     DropDownList1.Items.Insert(1, new ListItem(t2, "")); 
     DropDownList1.Items.Insert(2, new ListItem(t3, "")); 
     DropDownList1.Items.Insert(3, new ListItem(t4, "")); 
     DropDownList1.Items.Insert(4, new ListItem(t5, "")); 
     DropDownList1.Items.Insert(5, new ListItem(t6, "")); 
     DropDownList1.Items.Insert(6, new ListItem(t7, "")); 
     DropDownList1.Items.Insert(7, new ListItem(t8, "")); 
     DropDownList1.Items.Insert(8, new ListItem(t9, "")); 
     DropDownList1.Items.Insert(9, new ListItem(t10, "")); 
     DropDownList1.Items.Insert(10, new ListItem(t11, "")); 
     DropDownList1.Items.Insert(11, new ListItem(t12, "")); 
     DropDownList1.SelectedIndex = 4; 
    } 
    else if (t.Contains("/SE")) 
    { 
     t1 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/FI"; 
     t2 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/SE"; 
     t3 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/TH"; 
     t4 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/FO"; 
     t5 = t.Substring(0, 2) + "/FI"; 
     t6 = t.Substring(0, 2) + "/SE"; 
     t7 = t.Substring(0, 2) + "/TH"; 
     t8 = t.Substring(0, 2) + "/FO"; 
     t9 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/FI"; 
     t10 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/SE"; 
     t11 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/TH"; 
     t12 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/FO"; 
     DropDownList1.Items.Insert(0, new ListItem(t1, "")); 
     DropDownList1.Items.Insert(1, new ListItem(t2, "")); 
     DropDownList1.Items.Insert(2, new ListItem(t3, "")); 
     DropDownList1.Items.Insert(3, new ListItem(t4, "")); 
     DropDownList1.Items.Insert(4, new ListItem(t5, "")); 
     DropDownList1.Items.Insert(5, new ListItem(t6, "")); 
     DropDownList1.Items.Insert(6, new ListItem(t7, "")); 
     DropDownList1.Items.Insert(7, new ListItem(t8, "")); 
     DropDownList1.Items.Insert(8, new ListItem(t9, "")); 
     DropDownList1.Items.Insert(9, new ListItem(t10, "")); 
     DropDownList1.Items.Insert(10, new ListItem(t11, "")); 
     DropDownList1.Items.Insert(11, new ListItem(t12, "")); 
     DropDownList1.SelectedIndex = 5; 
    } 
    else if (t.Contains("/TH")) 
    { 
     t1 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/FI"; 
     t2 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/SE"; 
     t3 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/TH"; 
     t4 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/FO"; 
     t5 = t.Substring(0, 2) + "/FI"; 
     t6 = t.Substring(0, 2) + "/SE"; 
     t7 = t.Substring(0, 2) + "/TH"; 
     t8 = t.Substring(0, 2) + "/FO"; 
     t9 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/FI"; 
     t10 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/SE"; 
     t11 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/TH"; 
     t12 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/FO"; 
     DropDownList1.Items.Insert(0, new ListItem(t1, "")); 
     DropDownList1.Items.Insert(1, new ListItem(t2, "")); 
     DropDownList1.Items.Insert(2, new ListItem(t3, "")); 
     DropDownList1.Items.Insert(3, new ListItem(t4, "")); 
     DropDownList1.Items.Insert(4, new ListItem(t5, "")); 
     DropDownList1.Items.Insert(5, new ListItem(t6, "")); 
     DropDownList1.Items.Insert(6, new ListItem(t7, "")); 
     DropDownList1.Items.Insert(7, new ListItem(t8, "")); 
     DropDownList1.Items.Insert(8, new ListItem(t9, "")); 
     DropDownList1.Items.Insert(9, new ListItem(t10, "")); 
     DropDownList1.Items.Insert(10, new ListItem(t11, "")); 
     DropDownList1.Items.Insert(11, new ListItem(t12, "")); 
     DropDownList1.SelectedIndex = 6; 
    } 
    else if (t.Contains("/FO")) 
    { 
     t1 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/FI"; 
     t2 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/SE"; 
     t3 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/TH"; 
     t4 = (int.Parse(t.Substring(0, 2)) - 1).ToString() + "/FO"; 
     t5 = t.Substring(0, 2) + "/FI"; 
     t6 = t.Substring(0, 2) + "/SE"; 
     t7 = t.Substring(0, 2) + "/TH"; 
     t8 = t.Substring(0, 2) + "/FO"; 
     t9 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/FI"; 
     t10 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/SE"; 
     t11 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/TH"; 
     t12 = (int.Parse(t.Substring(0, 2)) + 1).ToString() + "/FO"; 
     DropDownList1.Items.Insert(0, new ListItem(t1, "")); 
     DropDownList1.Items.Insert(1, new ListItem(t2, "")); 
     DropDownList1.Items.Insert(2, new ListItem(t3, "")); 
     DropDownList1.Items.Insert(3, new ListItem(t4, "")); 
     DropDownList1.Items.Insert(4, new ListItem(t5, "")); 
     DropDownList1.Items.Insert(5, new ListItem(t6, "")); 
     DropDownList1.Items.Insert(6, new ListItem(t7, "")); 
     DropDownList1.Items.Insert(7, new ListItem(t8, "")); 
     DropDownList1.Items.Insert(8, new ListItem(t9, "")); 
     DropDownList1.Items.Insert(9, new ListItem(t10, "")); 
     DropDownList1.Items.Insert(10, new ListItem(t11, "")); 
     DropDownList1.Items.Insert(11, new ListItem(t12, "")); 
     DropDownList1.SelectedIndex = 7; 
    } 
}

有什么建议？
谢谢

来源

2017-08-24 Ali Aziz

你传入""（string.Empty）到ListItem构造：

DropDownList1.Items.Insert(0, new ListItem(t1, ""));

DropDownList控件必须具有有效的值设置（在浏览器中显示在列表中不只是文本）。这是通过DataValueField属性完成的。每个值必须是唯一的，否则最终只会选择第一个（重复）的情况。

检查HTML源代码在浏览器中，你应该有：

<select> 
    <option value="some_unique_value1">text1</option> 
    <option value="some_unique_value2">text2</option> 
</select>

你需要这些独特的价值观，因为它们是用于选择服务器上的正确项。

你有没有试过改变构造函数来传递一些独特的值？将""更改为Guid.NewGuid()或进行测试。

来源

2017-08-24 18:59:03 Patrick

Asp.net下拉列表问题

后面的代码：

回答

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