tiles.txt

main
    tiles::Tiles tiles(std::move(view_manager), view_owner.NewRequest(),startup_context.get(), border);
        view owner是view manager里的ViewImpl. view owner的服务端传给view manager了。

        root_node_.BindAsRequest(&root_export_token);
            ImportNode是要被import到别的node里去的。ImportNode有delegate node，用来addchild.
            别的export的node会收容这个ImportNode.
            NewImportResourceCmdAsRequest(id(), fuchsia::ui::gfx::ImportSpec::NODE, out_export_token)
                创建eventpair, 一头传出来交给要export的node，一头传给Scenic服务做import

            ====> scenic:
            Session::ApplyImportResourceCmd
                engine_->resource_linker()->ImportResource(import.get(), command.spec, std::move(command.token))
                    unresolved_imports_.AddUnresolvedImport
                resources_.AddResource
        
        view_manager_->CreateView(view_.NewRequest(), std::move(view_owner_request), view_listener_binding_.NewBinding(), std::move(root_export_token), "Tile");
            ====> view manager:
            
            ViewManagerImpl::CreateView
                registry_->CreateView
                    view_state->top_node().Export(std::move(parent_export_token));
                        把top node导出给上面导入,变成上面的root_node_
                
                    SchedulePresentSession
                        ====>
                        session_.Present

                    views_by_token_.emplace(view_state->view_token().value, view_state);

        view_->GetContainer(view_container_.NewRequest());
            ====> view manager
            ViewImpl::GetContainer

        view_container_->SetListener(view_container_listener_binding_.NewBinding());
            ====>
            ViewImpl::SetListener


    tiles.AddTilesByURL(command_line.positional_args());  // 这里要操作2个方面：一个是scenic方面的node的关系，另一个是view manager方面的view的树关系
        AddTileFromURL
            view_provider->CreateView(child_view_owner.NewRequest(), nullptr);
            AddChildView(child_key, std::move(child_view_owner), url, std::move(controller), allow_focus);
                view_data->host_node.ExportAsRequest
                    这里把host_node导出，后面viewstub会导入
                container_node_.AddChild(view_data->host_node);
                    把host node放入container

                view_container_->AddChild(child_key, std::move(child_view_owner), std::move(host_import_token));
                    ====> view manager
                    ViewImpl::AddChild
                        registry_->AddChild
                            ViewStub::ViewStub      view之间的树关系是由ViewStub和ViewContainerState来维护的
                                ====>
                                OnViewResolved(std::move(view_token), true);
                                    registry_->OnViewResolved
                                        AttachResolvedViewAndNotify
                                            view_stub->ImportHostNode(&session_);
                                            view_stub->host_node()->AddChild(view_state->top_node());
                            container_state->LinkChild

    presenter->Present(std::move(view_owner), nullptr);
        ====>
        App::Present
            Presentation1::Presentation1
            Presentation1::Present
                ====> self:
                Presentation1::CreateViewTree
                    view_manager_->CreateViewTree(tree_.NewRequest(), std::move(tree_listener), "Presentation");
                        ====> viewmanager:
                        registry_->CreateViewTree(std::move(view_tree_request), view_tree_listener.Bind(), label);
                            ViewTreeState::ViewTreeState


                    a11y_input_connection_->RegisterPresentation(std::move(token));
                        把viewtree的token给ally

                    view_manager_->CreateView(root_view_.NewRequest(), std::move(root_view_owner_request),std::move(root_view_listener), std::move(root_view_parent_export_token_),"RootView");

                    tree_container_->AddChild(kRootViewKey, std::move(root_view_owner), std::move(root_view_host_import_token_));
                        把root view加到view tree里，把这个presentation的root view host node导入给root view
                        view tree并不对应resource node, 所以view manager里的树关系不对应scenic里的node关系

                    root_container_->AddChild(kContentViewKey, std::move(view_owner), std::move(content_view_host_import_token_));
                        把要present的客户端view owner加入root view
                        把要present的客户端node加入content view node.