在MVVMLight框架的ViewModel中实现NavigationService

网上已经有很多方法了，比如通过Messenger来实现等等。这里我只讲述一种我比较喜欢的方法，因为它很方便

首先定义一个ViewModel基类，将所有ViewModel子类继承这个基类。在基类中定义

        protected bool RemoveBackEntry { get; set; }

        public NavigationService NavigationService { get; set; }

        public NavigationContext NavigationContext { get; set; }

        public virtual void OnNavigatedTo(NavigationEventArgs e) { }

        public virtual void OnNavigatingFrom(NavigatingCancelEventArgs e) { }

        public virtual void OnNavigatedFrom(NavigationEventArgs e)

        {

            if (RemoveBackEntry)

            {

                RemoveBackEntry = false;

                NavigationService.RemoveBackEntry();

            }

        }

因为在MVVM中，我们将会在所有页面上都加上DataContext，只要拿到DataContext就能拿到ViewModel，所以我们就可以定义子类WPhoneApplicationPage来继承PhoneApplicationPage这个类。

    public class WPhoneApplicationPage : PhoneApplicationPage

    {

        protected WPhoneApplicationPage()

        {

            Loaded += PageBaseLoaded;

        }





        private void PageBaseLoaded(object sender, RoutedEventArgs e)

        {

            var viewModel = DataContext as ViewModel.ViewModel;

            if (viewModel != null)

            {

                viewModel.NavigationService = NavigationService;

            }

        }



        protected override void OnNavigatedTo(NavigationEventArgs e)

        {

            base.OnNavigatedTo(e);



            var viewModel = DataContext as ViewModel.ViewModel;

            if (viewModel != null)

            {

                viewModel.NavigationContext = NavigationContext;

                viewModel.OnNavigatedTo(e);

            }

        }



        protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)

        {

            base.OnNavigatingFrom(e);

            var viewModel = DataContext as ViewModel.ViewModel;

            if (viewModel != null)

            {

                viewModel.NavigationContext = NavigationContext;

                viewModel.OnNavigatingFrom(e);

            }

        }



        protected override void OnNavigatedFrom(NavigationEventArgs e)

        {

            base.OnNavigatedFrom(e);

            var viewModel = DataContext as ViewModel.ViewModel;

            if (viewModel != null)

            {

                viewModel.NavigationContext = NavigationContext;

                viewModel.OnNavigatedFrom(e);

            }

        }

    }

　　这样在ViewModel中就可以调用NavigationService了。

　　此外，还需要修改View，让View继承WPhoneApplicationPage

　　xaml布局文件中

1 　<phone:WPhoneApplicationPage //修改PhoneApplicationPage 为 WPhoneApplicationPage

2 　　xmlns:phone="clr-namespace:redrock.Core" //这里是你的WPhoneApplicationPage类所在的命名空间

　　cs类文件中

public partial class MainPage : WPhoneApplicationPage // 让MainPage继承WPhoneApplicationPage

{

　　public MainPage()

　　{

　　　　InitializeComponent();

　　}

}

　　这样你可以在你的ViewModel中使用NavigationService以及重载 ViewModel基类中提供的导航方法