复杂的Document/View通讯

如果说要做一个多视图的程序，Document/View之间的通讯就变的稍微复杂一些。这时，就要用到UpdateAllViews和OnUpdate函数了。建立多视图程序的主要步骤如下：

1、定义CDocument派生类的成员变量，用于存储数据。

2、在CView派生类中重载OnUpdate函数，确保View中显示的内容与Document中的数据相同。

3、根据需要，组织Message Map。

4、在CView派生类的Command Message Handlers中根据需要更新Document的数据（用CView::GetDocument()函数），在最后要调用CDocument::UpdateAllViews函数以更新其他的View。

5、在CDocument派生类的Command Message Handlers中根据需要更新Document的数据，在最后同样要调用CDocument::UpdateAllViews函数以更新所有的View。

 

在通讯中将发生一下事件：

Application starts                                 CMyDocument object constructed
                                                              CMyView object constructed

                                                              Other view objects constructed
                                                              View windows created

                                                              CMyView::OnCreate called (if mapped)

                                                              CDocument::OnNewDocument called

                                                               CView::OnInitialUpdate called
                                                              Calls CMyView::OnUpdate
                                                              Initializes the view

 

User executes view command              CMyView functions update CMyDocument data members

                                                              Call CDocument::UpdateAllViews

                                                              Other views' OnUpdate functions called

                                                           

User executes document command     CMyDocument functions update data members

                                                              Call CDocument::UpdateAllViews

                                                              CMyView::OnUpdate called
                                                              Other views' OnUpdate functions called

                        

User exits application                           View objects destroyed
                                                               CMyDocument object destroyed