Code
public static class DataPageExtension
    {
        public static void BindSource(this DataPager dataPager, int totalCount, int pageSize)
        {
            List<int> list = new List<int>(totalCount);
            for (int i = 0; i < totalCount; i++) list.Add(i);
            PagedCollectionView pcv = new PagedCollectionView(list);
            pcv.PageSize = pageSize;
            dataPager.Source = pcv;
        }
    }

Code
 [OperationContract]
        public List<MyEmployee> GetEmployeeList(EmployeeFilter filter,out int totalCount)
        {
            using (TestDBEntities db = new TestDBEntities())
            {
                int rowsCount = 0;
                StringBuilder sbSql = new StringBuilder("True ");
                if (filter.DeptID != new Guid())
                    sbSql.Append(string.Format("and it.Departments.DepartmentID = Guid'{0}'", filter.DeptID));
                sbSql.Append(string.Format("and it.EmpolyeeName like '%{0}%'", filter.EmpName));

var query = from emp in db.Employees.Where(sbSql.ToString())
                            select new MyEmployee
                            {
                                ID = emp.EmployeeID,
                                Name = emp.EmpolyeeName,
                                Sex = emp.EmployeeSex ? "男" : "女",
                                Age = emp.EmployeeAge,
                                Address = emp.EmployeeAddress,
                                DeptName = emp.Departments.DepartmentName
                            };
                if (filter.PageIndex <= 0)
                    rowsCount = query.Count();
                totalCount = rowsCount;
                query = query.OrderBy(t => t.Name).Skip(filter.PageIndex * filter.PageSize).Take(filter.PageSize);
                return query.ToList();
            }
        }

Code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Data;
using DataPagerTest.EmployeeServiceReference;

namespace DataPagerTest
{
    public partial class MainPage : UserControl
    {
        EmployeeServiceClient client = new EmployeeServiceClient();
        EmployeeFilter filter = new EmployeeFilter();
        public MainPage()
        {
            InitializeComponent();
        }
        private void UserControl_Loaded(object sender, RoutedEventArgs e)
        {
            dpEmployee.PageIndexChanged += new EventHandler<EventArgs>(dpEmployee_PageIndexChanged);
            cbDept.SelectionChanged += new SelectionChangedEventHandler(cbDept_SelectionChanged);
            BindCombox();
        }

void cbDept_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            BindGrid(0);
        }
        void dpEmployee_PageIndexChanged(object sender, EventArgs e)
        {
            BindGrid(dpEmployee.PageIndex);
        }
        private void btnQuery_Click(object sender, RoutedEventArgs e)
        {
            BindGrid(0);
        }
        private void BindGrid(int pageIndex)
        {
            Departments dept = cbDept.SelectedItem as Departments;
            filter.DeptID = dept.DepartmentID;
            filter.EmpName = tbEmpName.Text.Trim();
            filter.PageIndex = pageIndex;
            filter.PageSize = 9;
            client.GetEmployeeListCompleted += new EventHandler<GetEmployeeListCompletedEventArgs>(client_GetEmployeeListCompleted);
            client.GetEmployeeListAsync(filter);
        }
        void client_GetEmployeeListCompleted(object sender, GetEmployeeListCompletedEventArgs e)
        {
            dgEmployee.ItemsSource = e.Result;
            if (filter.PageIndex <= 0)
                dpEmployee.BindSource(e.totalCount, filter.PageSize);
        }
        void BindCombox()
        {
            client.GetDepartmentListCompleted += new EventHandler<GetDepartmentListCompletedEventArgs>(client_GetDepartmentListCompleted);
            client.GetDepartmentListAsync();
        }

void client_GetDepartmentListCompleted(object sender, GetDepartmentListCompletedEventArgs e)
        {
            cbDept.ItemsSource = e.Result;
            cbDept.DisplayMemberPath = "DepartmentName";
            cbDept.SelectedIndex = 0;
            BindGrid(0);
        }

}
}