MVVMLight 实现指定Frame控件的导航

来源：互联网发布：Windows安装Python 编辑：程序博客网时间：2024/06/11 22:33

在UWP开发中，利用汉堡菜单实现导航是常见的方法。汉堡菜单导航一般都需要新建一个Frame控件，并对其进行导航，但是在MvvmLight框架默认的NavigationService中，只能对根Frame进行导航，这就需要我们实现自己的NavigationService了。

MvvmLight源码简析

GalaSoft.MvvmLight.Views命名空间下的NavigationService继承了同命名空间下的INavigationService接口但是并没有实现。

namespace GalaSoft.MvvmLight.Views{     public class NavigationService : INavigationService     {         public const string RootPageKey = "-- ROOT --";         public const string UnknownPageKey = "-- UNKNOWN --";         public NavigationService();         public string CurrentPageKey { get; }         public void Configure(string key, Type pageType);         public void GoBack();         public void NavigateTo(string pageKey);         public virtual void NavigateTo(string pageKey, object parameter);     }}

具体的功能实现是在GalaSoft.MvvmLight.Platform命名空间下的NavigationService中，根据平台的不同有不同的实现。
我们要做的就是自己实现INavigationService并自己定义导航的Frame控件

实现自己的NavigationService

很奇怪，官方公布源码的那个网站上没有找到Win10平台的Platform源码,所以我就把Win8.1的NavigationService实现复制下来，经测试能正常用。

在public virtual void NavigateTo(string pageKey, object parameter)方法下，我们可以看到这样一行代码：
var frame = ((Frame)Window.Current.Content);
这个语句就定义了用来导航的Frame控件（不止这个方法中有，另外2个方法中也有类似的语句）。
我们把这几个地方的frame变量值设置成自己的Frame控件就可以了。

我的修改方法：

我的Frame控件是放在MainPage中的，主要是为了实现汉堡菜单导航，我想大部分有这种需求的人都是为了实现类似的导航吧。

首先在MainPage.xaml.cs里面加入一个MainPage类型的静态Public变量
然后再构造函数中给变量赋值为this

还要给自己的Frame控件写一个属性来获取它

public static MainPage MPage;   // 1.public Frame MyFrame            // 3.{    get    {        return ContentFrame;    //ContentFrame是xaml中定义的Frame控件的名字    }}public MainPage(){    InitializeComponent();    SystemNavigationManager.GetForCurrentView().BackRequested += SystemNavigationManagerBackRequested;    Loaded += (s, e) =>    {        Vm.RunClock();    };    MPage = this;               // 2.}

然后就可以在自己的NavigationService里面使用自己的Frame了。
```
//var frame = ((Frame)Window.Current.Content);    // 之前的语句var frame = MainPage.MPage.MyFrame;               // 自己写的新语句
```
这样我们就把NavigationService的导航Frame设置成了MainPage里面的ContentFrame控件。

不过我这个方法还不是最优的，因为这样写就把MainPage和NavigationService直接联系起来了，增加了耦合性。我看到WPF中可以通过下面这个方法来获取指定名字的Frame控件，不过在UWP里面没有这个方法。
var frame = GetDescendantFromName(Application.Current.MainWindow, "MainFrame") as Frame;

如果谁有更好的办法的话麻烦在评论里面告诉我，万分感谢。

效果图

第一页

第二页

MyNavigationService代码

    using GalaSoft.MvvmLight.Views;    using Mvvm_HutHelper.View;    using System;    using System.Collections.Generic;    using System.Linq;    namespace Mvvm_HutHelper.Model    {        class MyNavigationService : 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 = ((Frame)Window.Current.Content);                        var frame = MainPage.MPage.MyFrame;                        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);                var frame = MainPage.MPage.MyFrame;                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 virtual 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 frame = ((Frame)Window.Current.Content);    // 这句设置导航时用到的Frame控件为根Frame                    var frame = MainPage.MPage.MyFrame;                    frame.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);                }            }        }    }

参考资料

MVVM Light 5.0: How to use the Navigation service

MvvmLight SourceCode

阅读全文

1 0