Atlas学习手记（12）：使用CascadingDropDown控件
CascadingDropDown通常叫作级联下拉菜单，本文将通过读取Northwind数据库中的Emplyee、Order、OrderDatail信息作为示例，来展示一下它的使用。
主要内容
1．CascadingDropDown控件介绍
2．从数据库读取数据并填充CascadingDropDown
一．CascadingDropDown控件介绍
CascadingDropDown通常叫作级联下拉菜单，本文将通过读取Northwind数据库中的Emplyee、Order、OrderDatail信息作为示例，来展示一下它的使用。示例代码如下：
<atlasToolkit:CascadingDropDown ID="CDD1" runat="server"> 
<atlasToolkit:CascadingDropDownProperties TargetControlID="DropDownList2" Category="Model" PromptText="Please select a model" LoadingText="[Loading models]" ServicePath="CarsService.asmx" ServiceMethod="GetDropDownContents" ParentControlID="DropDownList1" SelectedValue="SomeValue"> </atlasToolkit:CascadingDropDownProperties> </atlasToolkit:CascadingDropDown>对于CascadingDropDown需要为它添加CascadingDropDownProperties，有多少个下拉列表，就添加几个CascadingDropDownProperties，主要属性如下：
|
属性 |
说明 |
|
TargetControlID |
指定要扩展的DropDownList的ID |
|
Category |
DropDownList表示的类别名称，在WebMethod中会用到 |
|
PromptText |
没有选择时显示的文字 |
|
LoadingText |
加载数据时显示的文字 |
|
ServicePath |
获取数据的Web Service，为每个DropDownList都要指定 |
|
ServiceMethod |
获取数据的Web Method |
|
ParentControlID |
要扩展的DropDownList的父控件ID |
|
SelectedValue |
默认的选择项的值 |
二．从数据库读取数据并填充CascadingDropDown
下面用读取Northwind数据库中的Emplyee、Order、OrderDatail信息，看一个完整的示例。在新建一个Web Site后，先在页面的头部加上：
<%@ Register Assembly="AtlasControlToolkit" 
Namespace="AtlasControlToolkit" 
TagPrefix="atlasToolkit" %>加入三个DropDownList，分别用来显示Emplyee，Order，OrderDatail：
<div> <h3> Employee: <asp:DropDownList ID="ddlEmployees" runat="server" /><br /><br /> Order: <asp:DropDownList ID="ddlOrders" runat="server" /><br /><br /> Detail: <asp:DropDownList ID="ddlOrderDetails" runat="server" /> </h3></div>下面我们添加一个Northwind.asmx的Web Service，编写相关的Web Method：
[WebMethod]public CascadingDropDownNameValue[] GetEmployees( string knownCategoryValues, string category){ string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString; SqlConnection connection = new SqlConnection(connectionString); SqlCommand command = new SqlCommand("SELECT * FROM Employees"); command.Connection = connection; connection.Open(); SqlDataAdapter adapter = new SqlDataAdapter(command); DataSet dataSet = new DataSet(); adapter.Fill(dataSet); command.Connection.Close(); DataTable tbl = dataSet.Tables[0]; List<CascadingDropDownNameValue> values = new List<CascadingDropDownNameValue>(); foreach (DataRow dr in tbl.Rows)
{
string sEmployee = (string)dr["FirstName"] + " " + dr["LastName"]; int iEmployee = (int)dr["EmployeeID"]; values.Add(new CascadingDropDownNameValue( sEmployee, iEmployee.ToString()));
} return values.ToArray();}注意Web Method的参数签名是不可以改变的，并且它最后返回的是名-值对这种形式的数组。
整个完整后的Web Service如下：
完整代码 System;using System.Web;using System.Collections;using System.Configuration;using System.Collections.Generic;using System.Collections.Specialized;using System.Web.Services;using System.Web.Services.Protocols;using AtlasControlToolkit;using System.Data;using System.Data.SqlClient; /// <summary>/// Summary description for Northwind/// </summary>[WebService(Namespace = "http://tempuri.org/")][WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]public class Northwind : System.Web.Services.WebService { public Northwind () { //Uncomment the following line if using designed components //InitializeComponent(); } [WebMethod] public CascadingDropDownNameValue[] GetEmployees( string knownCategoryValues, string category) { string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString; SqlConnection connection = new SqlConnection(connectionString); SqlCommand command = new SqlCommand("SELECT * FROM Employees"); command.Connection = connection; connection.Open(); SqlDataAdapter adapter = new SqlDataAdapter(command); DataSet dataSet = new DataSet(); adapter.Fill(dataSet); command.Connection.Close(); DataTable tbl = dataSet.Tables[0]; List<CascadingDropDownNameValue> values = new List<CascadingDropDownNameValue>(); foreach (DataRow dr in tbl.Rows) { string sEmployee = (string)dr["FirstName"] + " " + dr["LastName"]; int iEmployee = (int)dr["EmployeeID"]; values.Add(new CascadingDropDownNameValue( sEmployee, iEmployee.ToString())); } return values.ToArray(); } [WebMethod] public CascadingDropDownNameValue[] GetOrdersByEmployee( string knownCategoryValues, string category) { StringDictionary kv = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues); int iEmployee; if (!kv.ContainsKey("Employee") || !Int32.TryParse(kv["Employee"], out iEmployee)) { return null; } string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString; SqlConnection connection = new SqlConnection(connectionString); SqlCommand command = new SqlCommand("SELECT OrderID FROM Orders WHERE EmployeeID = " + iEmployee); command.Connection = connection; connection.Open(); SqlDataAdapter adapter = new SqlDataAdapter(command); DataSet dataSet = new DataSet(); adapter.Fill(dataSet); command.Connection.Close(); DataTable tbl = dataSet.Tables[0]; List<CascadingDropDownNameValue> values = new List<CascadingDropDownNameValue>(); foreach (DataRow dr in tbl.Rows) { string sOrder = dr["OrderID"].ToString(); int iOrder = (int)dr["OrderID"]; values.Add(new CascadingDropDownNameValue( sOrder, iOrder.ToString())); } return values.ToArray(); } [WebMethod] public CascadingDropDownNameValue[] GetDetailsByOrder( string knownCategoryValues, string category) { StringDictionary kv = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues); int iOrder; if (!kv.ContainsKey("Order") || !Int32.TryParse(kv["Order"], out iOrder)) { return null; } string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString; SqlConnection connection = new SqlConnection(connectionString); SqlCommand command = new SqlCommand("SELECT UnitPrice,OrderID FROM [Order Details] WHERE OrderID = " + iOrder); command.Connection = connection; connection.Open(); SqlDataAdapter adapter = new SqlDataAdapter(command); DataSet dataSet = new DataSet(); adapter.Fill(dataSet); command.Connection.Close(); DataTable tbl = dataSet.Tables[0]; List<CascadingDropDownNameValue> values = new List<CascadingDropDownNameValue>(); foreach (DataRow dr in tbl.Rows) { string UnitPrice = dr["UnitPrice"].ToString(); int intOrder = (int)dr["OrderID"]; values.Add(new CascadingDropDownNameValue( UnitPrice, intOrder.ToString())); } return values.ToArray(); } }在Web.config中设置连接信息：
<connectionStrings> <add name="ConnectionString" connectionString="Data Source=RJ-097;User ID=sa;Password=sa;Initial Catalog=Northwind" providerName="System.Data.SqlClient"/></connectionStrings>这时我们再添加CascadingDropDown控件，设置它的属性如下：
<atlasToolkit:CascadingDropDown ID="CascadingDropDown1" runat="server"> <atlasToolkit:CascadingDropDownProperties Category="Employee" ParentControlID="" PromptText="Select Employee" SelectedValue="" ServiceMethod="GetEmployees" ServicePath="Northwind.asmx" TargetControlID="ddlEmployees" /> <atlasToolkit:CascadingDropDownProperties Category="Order" ParentControlID="ddlEmployees" PromptText="Select Order" SelectedValue="" ServiceMethod="GetOrdersByEmployee" ServicePath="Northwind.asmx" TargetControlID="ddlOrders" /> <atlasToolkit:CascadingDropDownProperties Category="OrderDetail" ParentControlID="ddlOrders" PromptText="Select OrderDetail" SelectedValue="" ServiceMethod="GetDetailsByOrder" ServicePath="Northwind.asmx" TargetControlID="ddlOrderDetails" /></atlasToolkit:CascadingDropDown>至此，大功告成。运行后效果如下：
选择：
