ASP.Net

Question

我想从单个数据 table 创建 cascading/dependent 下拉框。所有数据都在单个 table 中，例如国家、州、城市。

当用户 select 下拉列表框中的国家/地区状态应自动填写等等...

有许多使用不同 table 的示例，但如何使用单个 table 来做到这一点。请help/suggest/anylink.....

    string str5 = "SELECT distinct States FROM tblMain 
    da1 = new SqlDataAdapter(str5, con);
    dt1 = new DataTable();
    da1.Fill(dt1);
    ddlEmpName.DataSource = dt1;
    ddlEmpName.DataTextField = "States";
    ddlEmpName.DataValueField = "States";
    ddlEmpName.DataBind();

Answer 1

也许这会让您入门。所有数据都在一个 DataTable 中，并将显示在同一个 DropDownList 中。

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            //create a datatable with three columns
            DataTable dt = new DataTable();
            dt.Columns.Add("ID", typeof(int));
            dt.Columns.Add("Type", typeof(string));
            dt.Columns.Add("Name", typeof(string));

            //add nine datarows
            dt.Rows.Add(0, "Country", "Netherlands");
            dt.Rows.Add(1, "Country", "Japan");
            dt.Rows.Add(2, "Country", "America");
            dt.Rows.Add(3, "State", "Gelderland");
            dt.Rows.Add(4, "State", "Texas");
            dt.Rows.Add(5, "State", "Echizen");
            dt.Rows.Add(6, "City", "Amsterdam");
            dt.Rows.Add(7, "City", "Tokyo");
            dt.Rows.Add(8, "City", "New York");

            //save the table in a viewstate
            ViewState["myViewState"] = dt;

            //fill the dropdown
            fillDropDownList("Country");
        }
    }

    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        //split the SelectedValue to find the next type of data for the dropdown
        string[] valueArr = DropDownList1.SelectedValue.Split('_');
        string filterType = valueArr[1];

        //get the next type
        if (filterType == "Country")
        {
            filterType = "State";
        }
        else if (filterType == "State")
        {
            filterType = "City";
        }
        else
        {
            filterType = "Country";
        }

        Label1.Text += valueArr[0] + "<br>";

        //refill the dropdown
        fillDropDownList(filterType);
    }

    private void fillDropDownList(string filterType)
    {
        //get the viewstate and cast it as a datatable
        DataTable dt = ViewState["myViewState"] as DataTable;

        //filter the correct rows with Linq
        DataTable dtFiltered = dt.AsEnumerable().Where(row => row.Field<string>("Type") == filterType).CopyToDataTable();

        //clear the existing items in the dropdown
        DropDownList1.Items.Clear();

        //loop the filtered items and add them to the dropdown
        for (int i = 0; i < dtFiltered.Rows.Count; i++)
        {
            string text = dtFiltered.Rows[i][2].ToString();
            //make the value a combination of the name and type to split in SelectedIndexChanged
            string value = text + "_" + dtFiltered.Rows[i][1].ToString();

            DropDownList1.Items.Insert(i, new ListItem(text, value, true));
        }
        DropDownList1.Items.Insert(0, new ListItem("Select...", "", true));
    }

而在 aspx 页面中：

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged"></asp:DropDownList>
<br /><br />
<asp:Label ID="Label1" runat="server" Text=""></asp:Label>

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