prism journal导航按钮的可用性探索记录

prism使用导航功能的时候，跳了几个坑，记录一下。

1、导航记录的产生，是在区域导航过程中产生的。

_regionManager.Regions[PrismManager.MainViewRegionName].RequestNavigate(obj.NameSpace, back =>
{
journal= back.Context.NavigationService.Journal;

journalHistory();
});

2、通过journal.goback(),journal.goforward()来向前向后。

3、journal.CanGoback和Canforward来确定是否可导。

4、但是如果在命令中使用GobackCommand=new DelegateCommand(Goback,()=>journal.CanGoBack）话就不可以，因为这时候journal还是null。

5、测试成功的方法

private IRegionNavigationJournal journal;
 
        public MainWindowViewModel(IRegionManager regionManager)
        {
            _regionManager = regionManager;
            CreateMenuBar();
            NavigateCommand = new DelegateCommand<MenuBar>(Navigate);
 
            GoBackCommand = new DelegateCommand(goback).ObservesCanExecute(() => CanGoBack);
            GoForwardCommand = new DelegateCommand(goforward).ObservesCanExecute(() => CanGoForward);
        }
 
        
 
        private void goforward()
        {
            journal.GoForward();
            journalHistory();
        }
 
        private void goback()
        {
            journal.GoBack();
            journalHistory();
        }
 
        private void Navigate(MenuBar obj)
        {
            if (obj == null || string.IsNullOrEmpty(obj.NameSpace)) return;
            _regionManager.Regions[PrismManager.MainViewRegionName].RequestNavigate(obj.NameSpace, back =>
            {
                journal=  back.Context.NavigationService.Journal;
 
                journalHistory();
            });
            
        }
        private void journalHistory()
        {
            CanGoForward = journal.CanGoForward;
            CanGoBack = journal.CanGoBack;
        }