基于Asp.net与Javascript控制的日期控件

控件效果如下：

从左到右：month，day，year

.cs文件初始化这三个下拉列表

private void BindBirthDay(int day, int month, int year) 
{ 
int dayNow = day; 
int monNow = month; 
int yearNow = year; 
//binding Month 
for (int i = 1; i <= 12; i++) 
{ 
ddlBirMon.Items.Add(new ListItem(i.ToString(), i.ToString())); 
} 
ddlBirMon.Items[monNow - 1].Selected = true; 
//binding Day 
int daysOfMonth = DateTime.DaysInMonth(yearNow, monNow); 
for (int i = 1; i <= daysOfMonth; i++) 
{ 
ddlBirDay.Items.Add(new ListItem(i.ToString(), i.ToString())); 
} 
ddlBirDay.Items[dayNow - 1].Selected = true; 
//binding Year 
for (int i = 20; i > 0; i--) 
{ 
ddlBirYear.Items.Add(new ListItem((yearNow - i).ToString(), (yearNow - i).ToString())); 
} 
for (int i = 0; i < 20; i++) 
{ 
ddlBirYear.Items.Add(new ListItem((yearNow + i).ToString(), (yearNow + i).ToString())); 
} 
ddlBirYear.Items.FindByValue(yearNow.ToString()).Selected = true; 
}

js代码如下（自己写的，不保证完全正确啊）：

function ChangeDay() { 
var month = document.getElementById("<%=ddlBirMon.ClientID %>"); 
var year = document.getElementById("<%=ddlBirYear.ClientID %>"); 
var day = document.getElementById("<%=ddlBirDay.ClientID %>"); 
if (month.selectedIndex == 3 || month.selectedIndex == 5 || month.selectedIndex == 8 || month.selectedIndex == 10) { 
if (day.length == 31) { 
if (day.options[30].selected == true) { 
day.options[29].selected = true; 
} 
day.remove(30); 
} 
} 
else{ 
while (day.length < 31) { 
day.add(new Option(day.length+1,day.length+1)); 
} 
} 
if (month.selectedIndex == 1) { 
if (day.length > 28) { 
if (day.selectedIndex == 28) { 
day.options[27].selected = true; 
} 
while (day.length > 28) { 
day.remove(day.length - 1); 
} 
} 
var sy = year.options[year.selectedIndex].value; 
if ((sy % 4 == 0 && sy % 100 != 0) || (sy % 400==0)) { 
day.add(new Option("29", "29")); 
} 
} 
}