DomainDataSource学习笔记

（一）问题的提出 ： 

        在很多情况下，使用DomainDataSource比使用DomainContext对于数据获取要方便得多！就拿我前篇DataForm中的ComboBox下篇中就用到了DomainDataSource.只需要在前台的*.xaml中写上一句话ItemsSource="{Binding Path=Data,ElementName=employeeDomainDataSource}"就行了。本篇不着重讲解到底怎么方便，而是如果我们这句不写，而在后台代码中实现这个功能，该怎么实现？

（二）分析 ：

在解决这个问题我们必须搞清楚整个代码的执行顺序！经过测试发现执行流程如下：

（1）DepartmentDDS获取了Department中的所有值-->触发departmentDomainDataSource_LoadedData事件。
（2）employeeDomainDataSource获取了Employee中的所有值-->触发employeeDomainDataSource_LoadedData事件这，我们在该事件中获取就很方便了。
（3）进行每个Employee绑定,EmployeeID、EmployeeName、而到了部门DepartmentID时执行转换器DepartmentConvert.实现DepartmentID=>Department,这样Combobox的SelectedItem就先中了DepartmentID所对应的Department了。

（三）延伸：

用DomainDataSource进行的数据绑定很容，但是有时我们需要实现特殊的操作还是会用到DomainContext,要实现Combobox根据DepartmentID=>Department，还得把var query = from employee in client.GetEmployeesQuery().Where(p => p.EmployeeID == 1) select employee方在这里！放在其他的地方是不会实现该功能的。

（四）后台代码：

 

namespace ComboxInDataForm
{
    public partial class MainPage : UserControl
    {
        EmployeeContext client = new EmployeeContext();
        public MainPage()
        {
            InitializeComponent();
            this.Loaded += new RoutedEventHandler(MainPage_Loaded);
        }

        void MainPage_Loaded(object sender, RoutedEventArgs e)
        {
            this.dataForm1.EditTemplate = Resources["employeeTemplate"] as DataTemplate;
            //var query = from employee in client.GetEmployeesQuery().Where(p => p.EmployeeID == 1) select employee;
            //LoadOperation<Employee> lo = client.Load(query);
            //lo.Completed += new EventHandler(lo_Completed);  
        }       

        private void departmentDomainDataSource_LoadedData(object sender, System.Windows.Controls.LoadedDataEventArgs e)
        {
            if (e.HasError)
            {
                System.Windows.MessageBox.Show(e.Error.ToString(), "Load Error", System.Windows.MessageBoxButton.OK);
                e.MarkErrorAsHandled();
            }
        }

        private void employeeDomainDataSource_LoadedData(object sender, LoadedDataEventArgs e)
        {
            if (e.HasError)
            {
                System.Windows.MessageBox.Show(e.Error.ToString(), "Load Error", System.Windows.MessageBoxButton.OK);
                e.MarkErrorAsHandled();              
            }
            //方法一：用DomainDataSource实现Combobox功能
            //this.dataForm1.CurrentItem = employeeDomainDataSource.Data.Cast<Employee>().Where(p => p.EmployeeID ==3).FirstOrDefault();
            //方法二：使用DomainContext实现Combobox功能
            var query = from employee in client.GetEmployeesQuery().Where(p => p.EmployeeID == 1) select employee;
            LoadOperation<Employee> lo = client.Load(query);
            lo.Completed += new EventHandler(lo_Completed);  
        }
        void lo_Completed(object sender, EventArgs e)
        {
            LoadOperation<Employee> lo = sender as LoadOperation<Employee>;
            if (!lo.HasError)
            {
                if (lo.Entities.Count() > 0)
                {
                    this.dataForm1.CurrentItem = lo.Entities.FirstOrDefault();
                }
            }
            else
            {
                MessageBox.Show(lo.Error.Message);
            }

        }     

    }
}

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