用多个DropDownList分别来绑定多个年月日

首先看看效果：

年与月的数据源，较好定义，而日的数据源即需要根据年与月选择之后，方可获取到那年月的所有日数。如年：

 List<int> i_Year
    {
        get
        {
            List<int> y = new List<int>();
            int Ny = DateTime.Now.Year;
            for (int i = 1953; i <= Ny; i++)
            {
                y.Add(i);
            }
            return y;
        }
    }

月的数据源：

 List<int> i_Month
    {
        get
        {
            List<int> m = new List<int>();
            for (int i = 1; i <= 12; i++)
            {
                m.Add(i);
            }
            return m;
        }
    }

日的数据源：

public List<int> i_Day(int year, int month)
    {
        int days = DateTime.DaysInMonth(year, month);
        List<int> d = new List<int>();

        for (int i = 1; i <= days; i++)
        {
            d.Add(i);
        }
        return d;
    }

由于多个地方是DropDownList数据绑定，因此Insus.NET先写一个通用DropDownList数据绑定的方法：

 private void DropDownlistParse(DropDownList ddl, object dataSource, string dataTextField, string dataValueField)
    {
        ddl.DataSource = dataSource;
        ddl.DataTextField = dataTextField;
        ddl.DataValueField = dataValueField;
        ddl.DataBind();
        ddl.Items.Insert(0, new ListItem(string.Empty, string.Empty));
    }

这样的话，在需要绑定的地方，即管传入参数即可。如在Page_Load时，需要对年与月的DropDownList数据绑定：

  protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Data_Binding();
        }
    }

    private void Data_Binding()
    {
        DropDownlistParse(this.DropDownListYear, i_Year.Select(y => new { value = y }).ToList(), "value", "value");
        DropDownlistParse(this.DropDownListMonth, i_Month.Select(m => new { value = m }).ToList(), "value", "value");
        this.DropDownListDay.Items.Insert(0, new ListItem(string.Empty, string.Empty));
    }

在年或月DropDownlist控件有异动时，作相应对日的DropDownList控件数据绑定：

 protected void DropDownListYear_SelectedIndexChanged(object sender, EventArgs e)
    {
        DayDataBinding();
    }

    protected void DropDownListMonth_SelectedIndexChanged(object sender, EventArgs e)
    {
        DayDataBinding();
    }

    private void DayDataBinding()
    {
        if (this.DropDownListYear.SelectedIndex == -1 || string.IsNullOrEmpty (this.DropDownListYear.SelectedItem.Value)) return;
        if (this.DropDownListMonth.SelectedIndex == -1 || string.IsNullOrEmpty(this.DropDownListMonth.SelectedItem.Value)) return;
        
        int y = Convert.ToInt32(this.DropDownListYear.SelectedItem.Value);
        int m = Convert.ToInt32(this.DropDownListMonth.SelectedItem.Value);

        DropDownlistParse(this.DropDownListDay, i_Day(y, m).Select(d => new { value = d }).ToList(), "value", "value");
    }

我们还要为了获取年月日三个DropDownList控件的值，因此写还得写三个属性：

 private int? _year;
    private int? _month;
    private int? _day;

    public int? Year
    {
        get
        {
            if (ViewState["Year"] != null)
            {
                return Convert.ToInt32(ViewState["Year"]);
            }

            if (this.DropDownListYear.SelectedIndex == -1 || string.IsNullOrEmpty(this.DropDownListYear.SelectedItem.Value))
                return null;
            else
                return Convert.ToInt32(this.DropDownListYear.SelectedItem.Value);
        }
        set
        {
            ViewState["Year"] = value;
        }
    }

    public int? Month
    {
        get
        {
            if (ViewState["Month"] != null)
            {
                return Convert.ToInt32(ViewState["Month"]);
            }
            if (this.DropDownListMonth.SelectedIndex == -1 || string.IsNullOrEmpty(this.DropDownListMonth.SelectedItem.Value))
                return null;
            else
                return Convert.ToInt32(this.DropDownListMonth.SelectedItem.Value);

        }
        set
        {
            ViewState["Month"] = value;
        }
    }

    public int? Day
    {
        get
        {
            if (ViewState["Day"] != null)
            {
                return Convert.ToInt32(ViewState["Day"]);
            }
            if (this.DropDownListDay.SelectedIndex == -1 || string.IsNullOrEmpty(this.DropDownListDay.SelectedItem.Value))
                return null;
            else
                return Convert.ToInt32(this.DropDownListDay.SelectedItem.Value);
        }
        set
        {
            ViewState["Day"] = value;
        }
    }

最后是ASCX的html:

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="InsusDate.ascx.cs" Inherits="InsusDate" %>
<asp:DropDownList ID="DropDownListYear" runat="server" AutoPostBack="true" OnSelectedIndexChanged="DropDownListYear_SelectedIndexChanged" Width="60px"></asp:DropDownList>年<asp:DropDownList ID="DropDownListMonth" runat="server" AutoPostBack="true" OnSelectedIndexChanged="DropDownListMonth_SelectedIndexChanged" Width="40PX"></asp:DropDownList>月<asp:DropDownList ID="DropDownListDay" runat="server" Width="40PX"></asp:DropDownList>日

完整的ASCX.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class InsusDate : System.Web.UI.UserControl
{
    private int? _year;
    private int? _month;
    private int? _day;

    public int? Year
    {
        get
        {
            if (ViewState["Year"] != null)
            {
                return Convert.ToInt32(ViewState["Year"]);
            }

            if (this.DropDownListYear.SelectedIndex == -1 || string.IsNullOrEmpty(this.DropDownListYear.SelectedItem.Value))
                return null;
            else
                return Convert.ToInt32(this.DropDownListYear.SelectedItem.Value);
        }
        set
        {
            ViewState["Year"] = value;
        }
    }

    public int? Month
    {
        get
        {
            if (ViewState["Month"] != null)
            {
                return Convert.ToInt32(ViewState["Month"]);
            }
            if (this.DropDownListMonth.SelectedIndex == -1 || string.IsNullOrEmpty(this.DropDownListMonth.SelectedItem.Value))
                return null;
            else
                return Convert.ToInt32(this.DropDownListMonth.SelectedItem.Value);

        }
        set
        {
            ViewState["Month"] = value;
        }
    }

    public int? Day
    {
        get
        {
            if (ViewState["Day"] != null)
            {
                return Convert.ToInt32(ViewState["Day"]);
            }
            if (this.DropDownListDay.SelectedIndex == -1 || string.IsNullOrEmpty(this.DropDownListDay.SelectedItem.Value))
                return null;
            else
                return Convert.ToInt32(this.DropDownListDay.SelectedItem.Value);
        }
        set
        {
            ViewState["Day"] = value;
        }
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Data_Binding();
        }
    }

    private void Data_Binding()
    {
        DropDownlistParse(this.DropDownListYear, i_Year.Select(y => new { value = y }).ToList(), "value", "value");
        DropDownlistParse(this.DropDownListMonth, i_Month.Select(m => new { value = m }).ToList(), "value", "value");
        this.DropDownListDay.Items.Insert(0, new ListItem(string.Empty, string.Empty));
    }

    protected void DropDownListYear_SelectedIndexChanged(object sender, EventArgs e)
    {
        DayDataBinding();
    }

    protected void DropDownListMonth_SelectedIndexChanged(object sender, EventArgs e)
    {
        DayDataBinding();
    }

    private void DayDataBinding()
    {
        if (this.DropDownListYear.SelectedIndex == -1 || string.IsNullOrEmpty (this.DropDownListYear.SelectedItem.Value)) return;
        if (this.DropDownListMonth.SelectedIndex == -1 || string.IsNullOrEmpty(this.DropDownListMonth.SelectedItem.Value)) return;
        
        int y = Convert.ToInt32(this.DropDownListYear.SelectedItem.Value);
        int m = Convert.ToInt32(this.DropDownListMonth.SelectedItem.Value);

        DropDownlistParse(this.DropDownListDay, i_Day(y, m).Select(d => new { value = d }).ToList(), "value", "value");
    }

    private void DropDownlistParse(DropDownList ddl, object dataSource, string dataTextField, string dataValueField)
    {
        ddl.DataSource = dataSource;
        ddl.DataTextField = dataTextField;
        ddl.DataValueField = dataValueField;
        ddl.DataBind();
        ddl.Items.Insert(0, new ListItem(string.Empty, string.Empty));
    }

    List<int> i_Year
    {
        get
        {
            List<int> y = new List<int>();
            int Ny = DateTime.Now.Year;
            for (int i = 1953; i <= Ny; i++)
            {
                y.Add(i);
            }
            return y;
        }
    }

    List<int> i_Month
    {
        get
        {
            List<int> m = new List<int>();
            for (int i = 1; i <= 12; i++)
            {
                m.Add(i);
            }
            return m;
        }
    }

    public List<int> i_Day(int year, int month)
    {
        int days = DateTime.DaysInMonth(year, month);
        List<int> d = new List<int>();

        for (int i = 1; i <= days; i++)
        {
            d.Add(i);
        }
        return d;
    }
}

可以把ASCX保存为一个ASCX用户控件，在网页拉进去即可。