mvvm-light - 在Windows 8中使用MVVMLight通过ViewModel进行页面导航

Question

我上周刚开始使用mvvm light开发全新的Windows 8应用程序。我对mvvmlight WP7导航很熟悉。我如何在Windows 8中实现相同的功能。有人可以提出一种更好的方法在Windows 8中实现相同的功能。我找到了一种解决方案，其中我们覆盖了vm中的onnavigated事件并处理了导航到其他页面的问题。但是我认为这种方法已经过时了。任何人都可以指导我正确实现。提前致谢。

Answer 1

我了解这不是您要找的确切答案，但这可能会为您提供一些思路。

就我而言，我不是在使用MVVMLight-而是我自己的简单MVVM实现。我将BindableBase类(默认VS 2012 RC模板随附)用于属性通知。我想，您可以使用MVVMLight为您提供一些基础架构，并可以通过以下内容进行补充。

为了进行导航，我定义了一个界面，如下所示:

public interface INavigationService
{
    void Navigate(Type type);
    void Navigate(Type type, object parameter);
    void EnsureNavigated(Type pageType, object parameter);

    bool CanGoBack { get; }
    bool CanGoForward { get; }
    void GoBack();
    void GoForward(); 

    IView CurrentView { get; }
}

并实现如下:

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Windows.UI.Xaml.Controls;

public class NavigationService : INavigationService
{
    private readonly Frame _frame;

    public NavigationService(Frame frame)
    {
        _frame = frame;
        _frame.Navigated += OnFrameNavigated;
    }

    private void OnFrameNavigated(object sender, Windows.UI.Xaml.Navigation.NavigationEventArgs e)
    {
        var view = e.Content as IView;
        if (view == null)
            return;

        var navMsg = new NavigationMessage()
        {
            Sender = this,
            NewView = view,
            Parameter = e.Parameter,
            NavigationMode = (int)e.NavigationMode
        };

        EventManager.Current.Publish(navMsg);

        //Anything that the parent needs to be notified should happen in of after this method
        var viewModel = view.ViewModel;
        if (viewModel != null)
            viewModel.Initialise(e.Parameter);
    }

    public void Navigate(Type pageType)
    {
        DisposePreviousView();
        _frame.Navigate(pageType);
    }

    public void Navigate(Type pageType, object parameter)
    {
        DisposePreviousView();
        _frame.Navigate(pageType, parameter);
    }

    private void DisposePreviousView()
    {
        var currentView = this.CurrentView;
        var currentViewDisposable = currentView as IDisposable;
        if (currentViewDisposable != null)
        {
            currentViewDisposable.Dispose();
            currentViewDisposable = null;
        } //view model is disposed in the view implementation
    }

    public void EnsureNavigated(Type pageType, object parameter)
    {
        var currentView = this.CurrentView;
        if (currentView == null || currentView.GetType() != pageType)
        {
            Navigate(pageType, parameter);
        }
    }

    public IView CurrentView
    {
        get { return _frame.Content as IView; }
    }


    public bool CanGoBack
    {
        get { return _frame != null && _frame.CanGoBack; }
    }

    public void GoBack()
    {
        // Use the navigation frame to return to the previous page
        if (_frame != null && _frame.CanGoBack) _frame.GoBack();
    }

    public bool CanGoForward
    {
        get { return _frame != null && _frame.CanGoForward; }
    }

    public void GoForward()
    {
        // Use the navigation frame to return to the previous page
        if (_frame != null && _frame.CanGoForward) _frame.GoForward();
    }

}

IView:

public interface IView : IDisposable
{
    IViewModel ViewModel { get; }
    void Refresh();
}

IViewModel:

public interface IViewModel : INotifyPropertyChanged, IDisposable
{
    void Initialise(object parameter);
    string ViewTitle { get; }
    void Refresh();
}

最后，在XAML页面中，定义一个 Frame元素:

<Frame x:Name="ContentFrame" />

在页面的代码中:(这是我认为唯一丑陋的部分，但希望它不会太糟):

var _navigationService = new NavigationService(this.ContentFrame);

现在，您可以将 _navigationService传递给 View 模型。就我而言，我在页面的代码后面创建了viewmodel:

public HomePage()
{
    this.InitializeComponent();

    var _navigationService = NavigationService.GetFor(this.ContentFrame);

    DataContext = new HomePageViewModel(_navigationService);

}

希望这可以帮助。