使用C＃在asp.net中更改下拉列表选择的索引

Question

我有2个下拉列表。

首先是城市和
状态第二

我要在选择城市时填写州列表...

我正在使用代码

protected void Ddl_SelectedIndexChanged(object sender, EventArgs e)
    {

        String sqlQuery="select SM.StateId,StateName From StateMast SM,CityMast CM where CM.StateId=SM.StateId AND CM.CItyId='"+ Convert.ToInt16(DdlCity.SelectedValue.ToString())+"'";

        DdlState.DataSource = cls.Select(sqlQuery);
        DdlState.DataTextField = "StateName";
        DdlState.DataValueField = "StateId";
    }

但是选择城市没有障碍...

我设置了autopostback的city=true ..

Select是一个正在返回数据表的函数

public DataTable Select(String sqlQuery)
   {       
       con.Open();
       SqlDataAdapter adapter = new SqlDataAdapter(sqlQuery,con);
       DataTable table = new DataTable();
       adapter.Fill(table);
       con.Close();
       return table;
   }

Answer 1

设置数据源后，您没有调用DataBind() 。

protected void Ddl_SelectedIndexChanged(object sender, EventArgs e) {
    String sqlQuery="select SM.StateId,StateName From StateMast SM,CityMast CM where CM.StateId=SM.StateId AND CM.CItyId='"+ Convert.ToInt16(DdlCity.SelectedValue.ToString())+"'";

    DdlState.DataSource = cls.Select(sqlQuery);
    DdlState.DataTextField = "StateName";
    DdlState.DataValueField = "StateId";
    DdlState.DataBind();
}

编辑（带有验证器）：
ASPX：

<body>
    <form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="ddlCity" runat="server" AutoPostBack="true" 
            onselectedindexchanged="ddlCity_SelectedIndexChanged">
        </asp:DropDownList>
        <asp:RequiredFieldValidator ID="rfvCity" runat="server" ErrorMessage="City is required" ControlToValidate="ddlCity" InitialValue="0" Display="Dynamic"></asp:RequiredFieldValidator>
        <br />
        <asp:DropDownList ID="ddlState" runat="server" AutoPostBack="true">
        </asp:DropDownList>
        <asp:Button ID="Button1" runat="server" Text="Button" />
    </div>
    </form>
</body>

的.cs：

public partial class ChildDDL : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
            return;

        ddlCity.Items.Add(new ListItem("Select One", "0"));
        ddlCity.Items.Add(new ListItem("City 1", "1"));
        ddlCity.Items.Add(new ListItem("City 2", "2"));
        ddlCity.Items.Add(new ListItem("City 3", "3"));

        List<State> lstState = new List<State>();
        lstState.Add(new State() { StateID = 1, StateName = "State 1", CityID = 1 });
        lstState.Add(new State() { StateID = 2, StateName = "State 2", CityID = 1 });
        lstState.Add(new State() { StateID = 3, StateName = "State 3", CityID = 1 });
        lstState.Add(new State() { StateID = 4, StateName = "State 4", CityID = 2 });
        lstState.Add(new State() { StateID = 5, StateName = "State 5", CityID = 2 });
        lstState.Add(new State() { StateID = 6, StateName = "State 6", CityID = 2 });
        lstState.Add(new State() { StateID = 7, StateName = "State 7", CityID = 3 });
        lstState.Add(new State() { StateID = 8, StateName = "State 8", CityID = 3 });

        Session["lstState"] = lstState;
    }

    protected void ddlCity_SelectedIndexChanged(object sender, EventArgs e)
    {
        List<State> lstState = (List<State>)Session["lstState"];

        ddlState.DataSource = lstState
            .Where(state => state.CityID == Convert.ToInt32(ddlCity.SelectedValue)); ;
        ddlState.DataTextField = "StateName";
        ddlState.DataValueField = "StateID";
        ddlState.DataBind();
    }

    public class State
    {
        public int StateID { get; set; }
        public string StateName { get; set; }
        public int CityID { get; set; }
    }
}

该页面可与验证程序一起很好地工作。

Answer 2

尝试在您的下拉列表属性中设置Autopostback = true

Answer 3

您可以使用以下代码：

foreach (ListItem item in YourDropDownList.Items)
 {
        if (item.Text == defaultText) 
        {
            item.Selected = true;
            break;
        }
 }

Answer 4

我已经做了类似的案例，使用Category DropDownList和Product DropDownList来显示与所选类别相关的不同产品，并且每次用户选择类别时，列表都会更改。

首先，将源（在我的情况下为Category，在您的情况下为City）的AutoPostBack设置为True。

在SelectedIndexChanged事件上：

if ( DdlCity.SelectedValue != null ) {
    String sqlQuery="select SM.StateId,StateName From StateMast SM,CityMast CM where CM.StateId=SM.StateId AND CM.CItyId='"+ Convert.ToInt16(DdlCity.SelectedValue.ToString())+"'";

    // Try to get the DataTable first
    DataTable data = cls.Select(sqlQuery);

    // I assume there is a Label name lblNumOfData
    lblNumOfData.Text = String.Format("There is {0} state", data.Rows.Count);

    DdlState.DataSource = data;
    DdlState.DataValueField = "StateId";
    DdlState.DataTextField = "StateName";
    DdlState.DataBind();
}

该代码应该能够显示状态列表，但是，如果仍然看不到状态，则添加代码以确保函数Select返回了数据。

Answer 5

我认为您必须更新DropDown所在的更新面板...为什么不使用AJAX控件工具包级联DropDown？ 它们是针对与您相同的场景而构建的。

http://www.asp.net/ajax/ajaxcontroltoolkit/samples/CascadingDropDown/CascadingDropDown.aspx

使用C＃在asp.net中更改下拉列表选择的索引

问题描述

5 个解决方案

解决方案1
2 2010-10-12 06:57:02

解决方案2
1 2013-03-19 03:41:33

解决方案3
0 2013-01-24 08:24:54

解决方案4
0 2013-03-19 04:20:47

解决方案5
0 2010-10-12 07:14:02

使用C＃在asp.net中更改下拉列表选择的索引

问题描述

5 个解决方案

解决方案1 2 2010-10-12 06:57:02

解决方案2 1 2013-03-19 03:41:33

解决方案3 0 2013-01-24 08:24:54

解决方案4 0 2013-03-19 04:20:47

解决方案5 0 2010-10-12 07:14:02

解决方案1
2 2010-10-12 06:57:02

解决方案2
1 2013-03-19 03:41:33

解决方案3
0 2013-01-24 08:24:54

解决方案4
0 2013-03-19 04:20:47

解决方案5
0 2010-10-12 07:14:02