Windows.UI.Xaml.Controls.Frame'在win10通用应用中使用mvvm-light导航

我和Laurent Bugnion谈过，他建议我实现自己的导航服务，由他来处理导航。为此，我制作了一个PageNavigationService，它实现了MVVM Light的INavigationService接口。

public class PageNavigationService : INavigationService
{
    /// <summary>
    ///     The key that is returned by the <see cref="CurrentPageKey" /> property
    ///     when the current Page is the root page.
    /// </summary>
    public const string RootPageKey = "-- ROOT --";
    /// <summary>
    ///     The key that is returned by the <see cref="CurrentPageKey" /> property
    ///     when the current Page is not found.
    ///     This can be the case when the navigation wasn't managed by this NavigationService,
    ///     for example when it is directly triggered in the code behind, and the
    ///     NavigationService was not configured for this page type.
    /// </summary>
    public const string UnknownPageKey = "-- UNKNOWN --";
    private readonly Dictionary<string, Type> _pagesByKey = new Dictionary<string, Type>();
    /// <summary>
    ///     The key corresponding to the currently displayed page.
    /// </summary>
    public string CurrentPageKey
    {
        get
        {
            lock (_pagesByKey)
            {
                var frame = ((AppShell) Window.Current.Content).AppFrame;
                if (frame.BackStackDepth == 0)
                {
                    return RootPageKey;
                }
                if (frame.Content == null)
                {
                    return UnknownPageKey;
                }
                var currentType = frame.Content.GetType();
                if (_pagesByKey.All(p => p.Value != currentType))
                {
                    return UnknownPageKey;
                }
                var item = _pagesByKey.FirstOrDefault(
                    i => i.Value == currentType);
                return item.Key;
            }
        }
    }
    /// <summary>
    ///     If possible, discards the current page and displays the previous page
    ///     on the navigation stack.
    /// </summary>
    public void GoBack()
    {
        var frame = ((Frame) Window.Current.Content);
        if (frame.CanGoBack)
        {
            frame.GoBack();
        }
    }
    /// <summary>
    ///     Displays a new page corresponding to the given key.
    ///     Make sure to call the <see cref="Configure" />
    ///     method first.
    /// </summary>
    /// <param name="pageKey">
    ///     The key corresponding to the page
    ///     that should be displayed.
    /// </param>
    /// <exception cref="ArgumentException">
    ///     When this method is called for
    ///     a key that has not been configured earlier.
    /// </exception>
    public void NavigateTo(string pageKey)
    {
        NavigateTo(pageKey, null);
    }
    /// <summary>
    ///     Displays a new page corresponding to the given key,
    ///     and passes a parameter to the new page.
    ///     Make sure to call the <see cref="Configure" />
    ///     method first.
    /// </summary>
    /// <param name="pageKey">
    ///     The key corresponding to the page
    ///     that should be displayed.
    /// </param>
    /// <param name="parameter">
    ///     The parameter that should be passed
    ///     to the new page.
    /// </param>
    /// <exception cref="ArgumentException">
    ///     When this method is called for
    ///     a key that has not been configured earlier.
    /// </exception>
    public void NavigateTo(string pageKey, object parameter)
    {
        lock (_pagesByKey)
        {
            if (!_pagesByKey.ContainsKey(pageKey))
            {
                throw new ArgumentException(
                    string.Format(
                        "No such page: {0}. Did you forget to call NavigationService.Configure?",
                        pageKey),
                    "pageKey");
            }
            var shell = ((AppShell) Window.Current.Content);
            shell.AppFrame.Navigate(_pagesByKey[pageKey], parameter);
        }
    }
    /// <summary>
    ///     Adds a key/page pair to the navigation service.
    /// </summary>
    /// <param name="key">
    ///     The key that will be used later
    ///     in the <see cref="NavigateTo(string)" /> or <see cref="NavigateTo(string, object)" /> methods.
    /// </param>
    /// <param name="pageType">The type of the page corresponding to the key.</param>
    public void Configure(string key, Type pageType)
    {
        lock (_pagesByKey)
        {
            if (_pagesByKey.ContainsKey(key))
            {
                throw new ArgumentException("This key is already used: " + key);
            }
            if (_pagesByKey.Any(p => p.Value == pageType))
            {
                throw new ArgumentException(
                    "This type is already configured with key " + _pagesByKey.First(p => p.Value == pageType).Key);
            }
            _pagesByKey.Add(
                key,
                pageType);
        }
    }
}

基本上是他的实现的副本。但是我不是解析到一个Frame，而是解析到一个AppShell，并使用AppFrame属性来导航。

我把这个放到我的ViewModelLocator。而不是:

var navigationService = new NavigationService();

我将使用:

var navigationService = new PageNavigationService();

编辑:我注意到在NavMenuListView中有一个例外，当你使用新的navigationservice导航后使用背键，因为所选的项目是空的。我通过调整SetSelectedItem方法并在转换后的for循环中添加nullcheck来修复它:

    public void SetSelectedItem(ListViewItem item)
    {
        var index = -1;
        if (item != null)
        {
            index = IndexFromContainer(item);
        }
        for (var i = 0; i < Items.Count; i++)
        {
            var lvi = (ListViewItem) ContainerFromIndex(i);
            if(lvi == null) continue;
            if (i != index)
            {
                lvi.IsSelected = false;
            }
            else if (i == index)
            {
                lvi.IsSelected = true;
            }
        }
    }

但是可能有比这更优雅的解决方案