使用C＃在asp.net中更改下拉列表選擇的索引

Question

我有2個下拉列表。

首先是城市和
狀態第二

我要在選擇城市時填寫州列表...

我正在使用代碼

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";
    }

但是選擇城市沒有障礙...

我設置了autopostback的city=true ..

Select是一個正在返回數據表的函數

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

設置數據源后，您沒有調用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();
}

編輯（帶有驗證器）：
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; }
    }
}

該頁面可與驗證程序一起很好地工作。

Answer 2

嘗試在您的下拉列表屬性中設置Autopostback = true

Answer 3

您可以使用以下代碼：

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

Answer 4

我已經做了類似的案例，使用Category DropDownList和Product DropDownList來顯示與所選類別相關的不同產品，並且每次用戶選擇類別時，列表都會更改。

首先，將源（在我的情況下為Category，在您的情況下為City）的AutoPostBack設置為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();
}

該代碼應該能夠顯示狀態列表，但是，如果仍然看不到狀態，則添加代碼以確保函數Select返回了數據。

Answer 5

我認為您必須更新DropDown所在的更新面板...為什么不使用AJAX控件工具包級聯DropDown？ 它們是針對與您相同的場景而構建的。

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

使用C＃在asp.net中更改下拉列表選擇的索引

問題描述

5 個解決方案

解決方案1
2 2010-10-12 06:57:02

解決方案2
1 2013-03-19 03:41:33

解決方案3
0 2013-01-24 08:24:54

解決方案4
0 2013-03-19 04:20:47

解決方案5
0 2010-10-12 07:14:02

使用C＃在asp.net中更改下拉列表選擇的索引

問題描述

5 個解決方案

解決方案1 2 2010-10-12 06:57:02

解決方案2 1 2013-03-19 03:41:33

解決方案3 0 2013-01-24 08:24:54

解決方案4 0 2013-03-19 04:20:47

解決方案5 0 2010-10-12 07:14:02

解決方案1
2 2010-10-12 06:57:02

解決方案2
1 2013-03-19 03:41:33

解決方案3
0 2013-01-24 08:24:54

解決方案4
0 2013-03-19 04:20:47

解決方案5
0 2010-10-12 07:14:02