Question

我想在DropDownList ddlKlasse的SelectedValue为true时显示一个表。我使用带有母版页的asp.net空网页表单。这个想法是：

当ddlKlasse.SelectedValue =＆＃34; 2＆＃34; table tblDubbelTwee必须显示
当ddlKlasse.SelectedValue =＆＃34; 5＆＃34;必须显示table tblVierMet
当ddlKlasse.SelectedValue =＆＃34; 9＆＃34;必须显示表tblAchtMet

我从数据库中获取了下拉列表中的值。

我现在的代码是：

在我的Page_Load中：

protected void Page_Load(object sender, EventArgs e)
    {
        BindDropDownListKlasse();
        BindDropDownListVereniging();


        if (!Page.IsPostBack)
        {
            tblDubbelTwee.Visible = false;
            tblVierMet.Visible = false;
            tblAchtMet.Visible = false;


        }
    }

用于绑定下拉列表：

private void BindDropDownListKlasse()
    {
        try
        {
            using (SqlConnection conn = new SqlConnection(connString))
            {
                using (SqlCommand com = new SqlCommand())
                {
                    com.CommandText = "SELECT DISTINCT AantalDeelnemers, Naam FROM Klasse;";
                    com.Connection = conn;
                    conn.Open();
                    SqlDataAdapter da = new SqlDataAdapter(com);
                    DataTable dt = new DataTable();
                    da.Fill(dt);
                    ddlKlasse.DataSource = dt;
                    ddlKlasse.DataValueField = "AantalDeelnemers";
                    ddlKlasse.DataTextField = "Naam";
                    ddlKlasse.DataBind();
                    conn.Close();

                    //Adding "Kies de klasse" optie in dropdownlist voor validatie
                    ddlKlasse.Items.Insert(0, new ListItem("Kies de klasse", "0"));
                }
            }
        }
        catch
        {

        }
    }

用于显示表格：

protected void ddlKlasse_SelectedIndexChanged(object sender, EventArgs e)
    {
        ListItem selectedListItemDubbelTwee = ddlKlasse.Items.FindByValue("2");
        if (selectedListItemDubbelTwee != null)
        {
            selectedListItemDubbelTwee.Selected = true;
            tblDubbelTwee.Visible = true;
            tblVierMet.Visible = false;
            tblAchtMet.Visible = false;
        };

        ListItem selectedListItemVierMet = ddlKlasse.Items.FindByValue("5");
        if (selectedListItemVierMet != null)
        {
            selectedListItemVierMet.Selected = true;
            tblVierMet.Visible = true;
            tblDubbelTwee.Visible = false;
            tblAchtMet.Visible = false;
        };

        ListItem selectedListItemAchtMet = ddlKlasse.Items.FindByValue("9");
        if (selectedListItemAchtMet != null)
        {
            selectedListItemAchtMet.Selected = true;
            tblAchtMet.Visible = true;
            tblDubbelTwee.Visible = false;
            tblVierMet.Visible = false;
        };
    }

我的DropDownList：

<div class="form-inline">
    <div class="form-group">
        <asp:DropDownList ID="ddlKlasse" class="form-control" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlKlasse_SelectedIndexChanged"></asp:DropDownList>
    </div>
</div>

我的一张桌子：

<asp:Table ID="tblDubbelTwee" runat="server" class="table">
    <asp:TableHeaderRow>
        <asp:TableHeaderCell>Naam</asp:TableHeaderCell>
        <asp:TableHeaderCell>Email</asp:TableHeaderCell>
        <asp:TableHeaderCell>Lidmaatschapsnr</asp:TableHeaderCell>
    </asp:TableHeaderRow>

    <asp:TableRow>
        <asp:TableCell>
            <asp:TextBox ID="txtNaam" type="text" class="form-control" runat="server"></asp:TextBox>
        </asp:TableCell>
        <asp:TableCell>
            <asp:TextBox ID="txtEmail" type="text" class="form-control" runat="server"></asp:TextBox>
        </asp:TableCell>
        <asp:TableCell>
            <asp:TextBox ID="txtLidmaatschapsnr" type="text" class="form-control" runat="server"></asp:TextBox>
        </asp:TableCell>
    </asp:TableRow>
    <asp:TableRow>
        <asp:TableCell>
            <asp:TextBox ID="txtNaam2" type="text" class="form-control" runat="server"></asp:TextBox>
        </asp:TableCell>
        <asp:TableCell>
            <asp:TextBox ID="txtEmail2" type="text" class="form-control" runat="server"></asp:TextBox>
        </asp:TableCell>
        <asp:TableCell>
            <asp:TextBox ID="txtLidmaatschapsnr2" type="text" class="form-control" runat="server"></asp:TextBox>
        </asp:TableCell>
    </asp:TableRow>
</asp:Table>

但是当我运行我的项目并在我的DropDownList中选择一个字段时，它会给出错误：System.Web.HttpException：不允许在DropDownList中选择多个项目。

你能帮我解决这个问题吗？

Answer 1

您当前的DDL索引更改处理程序正在执行与您所描述的完全不同的操作。它基本上检查列表项是否存在于ddl列表中（无论是否选中），然后尝试选择它。由于存在3个项目，因此您实际上是在尝试选择3个项目，这是不允许的。

您可能正在寻找的是按所选值切换：

switch (ddlKlasse.SelectValue)
{
    case "2":
            tblDubbelTwee.Visible = true;
            tblVierMet.Visible = false;
            tblAchtMet.Visible = false;
            break;
    case "5": //similar here
    case "9": //similar here
    default:
    // exception or something
}

Answer 2

refere this code  
protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                bindgrid();

            }
        }

        void bindgrid()
        {
            con.Open();
            SqlCommand cmd = new SqlCommand("select DISTINCT Class from addmitionform1", con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
            con.Close();
            ddlclass.DataSource = ds;
            ddlclass.DataTextField = "Class";
            ddlclass.DataValueField = "Class";
            ddlclass.DataBind();
            ddlclass.Items.Insert(0, new ListItem("--Select--", "0"));

        }

protected void ddlKlasse_SelectedIndexChanged(object sender, EventArgs e)
    {
          string id = (ddlclass.SelectedValue.ToString());
            con.Close();
            SqlDataAdapter da1 = new SqlDataAdapter("Select id,FirstName from addmitionform1 where Class= '" + id + "'", con);
            //SqlDataAdapter da1 = new SqlDataAdapter("Select * from addmitionform1 ", con);
            DataSet ds1 = new DataSet();
            da1.Fill(ds1);
            GridView1.DataSource = ds1;
            GridView1.DataBind();
    }

Answer 3

首先在BindDropDownListKlasse()内移动BindDropDownListVereniging()和if (!IsPostBack)，正如HarveySpecter建议的那样。
并将ddlKlasse_SelectedIndexChanged()更改为：

protected void ddlKlasse_SelectedIndexChanged(object sender, EventArgs e)
{
    bool showDubbelTwee = false, showVierMet = false, showAchtMet = false;
    switch (ddlKlasse.SelectedValue)
    {
        case "2":
            showDubbelTwee = true;
            break;
        case "5":
            showVierMet = true;
            break;
        case "9":
            showAchtMet = true;
            break;
    }

    tblAchtMet.Visible = showVierMet;
    tblDubbelTwee.Visible = showDubbelTwee;
    tblVierMet.Visible = showVierMet;
}

您现在在ddlKlasse_SelectedIndexChanged()中正在执行的操作是检查下拉列表中是否存在每个值，如果存在，请选择它并显示相应的表格。
相反，您需要检查选择了哪个值并显示相应的表格。

当DropDownList的SelectedValue为true时显示表C＃

3 个答案: