本節學習了PRism中的UI Composition（界面組合），我認為里面最用的一個問題就是父視圖區域如何把上下文(RegionContext)傳到子視圖,且子視圖如何從獲得的RegionContext中獲取數據的。

   本文以UI Composition QuickStart為列說明這個問題。

（一）先看看這個項目的UI結構。

（二）父區域與子區域的區域上下文（RegionContext）過程簡介

       首先在EmployeeSummaryView.xaml中TabControl添加如下代碼：

  <!--TabControl定義為一個區域, 包含EmployeeDetailsView 和 EmployeeProjectsView 將被顯示-->        <!--TabControl定義了 RegionContext，綁定了當前EmployeeListView中選中的Employee項-->        <sdk:TabControl Grid.Row="1" AutomationProperties.AutomationId="EmployeeSummaryTabControl" Margin="8"                        prism:RegionManager.RegionName="TabRegion"                        prism:RegionManager.RegionContext="{Binding CurrentEmployee}"                        Width="Auto" Height="Auto" HorizontalAlignment="Stretch">            <prism:TabControlRegionAdapter.ItemContainerStyle>                <Style TargetType="sdk:TabItem">                    <Setter Property="HeaderTemplate">                        <Setter.Value>                            <!--顯示里面子視圖TabItem的TabHead-->                            <DataTemplate>                                <TextBlock Text="{Binding ViewName}" />                            </DataTemplate>                        </Setter.Value>                    </Setter>                </Style>            </prism:TabControlRegionAdapter.ItemContainerStyle>        </sdk:TabControl>    </Grid>
（三）在EmployeeProjectsView.xaml.cs中添加如下代碼：EmployeeDetailsView.xaml.cs相似
 public EmployeeProjectsView(EmployeeProjectsViewModel employeeProjectsViewModel)        {            this.InitializeComponent();            // Set the ViewModel as this View's data context.            this.DataContext = employeeProjectsViewModel;            //在視圖間共享上下文            //（1）區域上下文(RegionContext)：主要用于父視圖與子視圖間的數據傳遞            //    本例，主要是EmployeeSummaryView中的TabRegion與包含在里面兩個子視圖EmployeeDetailsView.xaml和EmployeeProjiectsView的數據傳遞            //(2)在視圖中獲取區域上下文（RegionContext）,需使用GetObservableContext方法            //(3)上下文的值可以更改，通過指定一個新的值給Value屬性            //(4)不能用使用DataContext屬性用于父視圖和子視圖的數據傳遞，以為DataContext只是用于View和ViewModel間的數據傳遞                      RegionContext.GetObservableContext(this).PropertyChanged += (s, e)                                                                        =>                                                                        employeeProjectsViewModel.CurrentEmployee =                                                                        RegionContext.GetObservableContext(this).Value                                                                        as Employee;        }
（四）關于 視圖發現（View Discovery）與 視圖注入(View Injection)
//視圖發現（View Discovery）與 視圖注入(View Injection)    //(1)視圖發現（View Discovery）允許將視圖(View)拉人(pull)到區域（Regions）中    //   RegionViewRegistry查找一個已經創建區域與之關聯的所有視圖(View)，匹配好的View被創建，并被拉入(pull)到區域中    //   當使用這中方法，region實例不能通過名字被明確地找到來創建view和注冊視圖到region    //   通常那些宿主在其他視圖的視圖有上下文需要可以被其子視圖得到    //(2)視圖注入(View Injection)方式:允許將視圖推入到已經存在的區域,這個需要建立一個視圖實例獲得視圖的引用，通過    //    RegionViewRegistry 使用region的Add方法將view和region相關聯    //    通常視圖注入（View Injection）被用作當明確空間的視圖作為一個區域是必要的，或者在算法上確定視圖什么時候ibie顯示。    //View Discovery和 View Injiection的不同    //(1)view discovery沒有時間議題，比如，一個module視圖加入一個view到一個還沒有被創建的region中。    //(2)能很簡單的檢查到多個實例額在同一區域中，因為你不需要知道限制的區域的管理者找指定的region實例去注冊你的視圖    //(3)你可以通過RegionViewRegistry類得GetContents方法得到所有的視圖關聯到特定的區域.    //(4)如果你需要限制區域管理你不應該用View Discorery組合，你需要要多個同時包含在同一起區域相同View的實例，因為一個區域通過    //  regionManager,名字必須唯一    public class ModuleInit : IModule    {        private readonly IUnityContainer container;        private readonly IRegionManager  regionManager;        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1823:AvoidUnusedPrivateFields")]        private MainRegionController _mainRegionController;        public ModuleInit(IUnityContainer container, IRegionManager regionManager)        {            this.container     = container;            this.regionManager = regionManager;        }        public void Initialize()        {            // Register the EmployeeDataService concrete type with the container.            // Change this to swap in another data service implementation.            this.container.RegisterType<IEmployeeDataService, EmployeeDataService>();            // This is an example of View Discovery which associates the specified view type            // with a region so that the view will be automatically added to the region when            // the region is first displayed.            // TODO: 03 - The EmployeeModule configures the EmployeeListView to automatically appear in the Left region (using View Discovery).            // Show the Employee List view in the shell's left hand region.            this.regionManager.RegisterViewWithRegion( RegionNames.LeftRegion,                                                       () => this.container.Resolve<EmployeeListView>());            // TODO: 04 - The EmployeeModule defines a controller class, MainRegionController, which programmatically displays views in the Main region (using View Injection).            // Create the main region controller.            // This is used to programmatically coordinate the view            // in the main region of the shell.            this._mainRegionController = this.container.Resolve<MainRegionController>();            // TODO: 08 - The EmployeeModule configures the EmployeeDetailsView and EmployeeProjectsView to automatically appear in the Tab region (using View Discovery).            // Show the Employee Details and Employee Projects view in the tab region.            // The tab region is defined as part of the Employee Summary view which is only            // displayed once the user has selected an employee in the Employee List view.            this.regionManager.RegisterViewWithRegion( RegionNames.TabRegion,                                                       () => this.container.Resolve<EmployeeDetailsView>());            this.regionManager.RegisterViewWithRegion (RegionNames.TabRegion,                                                       () => this.container.Resolve<EmployeeProjectsView>());        }    }
 （五）項目結構