.NET Core 3 WPF MVVM框架 Prism系列之导航系统
本文将介绍如何在.NET Core3环境下使用MVVM框架Prism基于区域Region的导航系统
在讲解Prism导航系统之前，我们先来看看一个例子,我在之前的demo项目创建一个登录界面：
我们看到这里是不是一开始想象到使用WPF带有的导航系统，通过Frame和Page进行页面跳转，然后通过导航日志的GoBack和GoForward实现后退和前进，其实这是通过使用Prism的导航框架实现的,下面我们来看看如何在Prism的MVVM模式下实现该功能
一.区域导航#
我们在上一篇介绍了Prism的区域管理，而Prism的导航系统也是基于区域的，首先我们来看看如何在区域导航
1.注册区域#
LoginWindow.xaml：
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xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:PrismMetroSample.Shell.Views.Login"
xmlns:region="clr-namespace:PrismMetroSample.Infrastructure.Constants;assembly=PrismMetroSample.Infrastructure"
mc:Ignorable="d"
xmlns:prism="http://prismlibrary.com/"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
Height="600" Width="400" prism:ViewModelLocator.AutoWireViewModel="True" ResizeMode="NoResize" WindowStartupLocation="CenterScreen"
Icon="pack://application:,,,/PrismMetroSample.Infrastructure;Component/Assets/Photos/Home, homepage, menu.png" >
<i:Interaction.Triggers>
<i:EventTrigger EventName="Loaded">
<i:InvokeCommandAction Command="{Binding LoginLoadingCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
<Grid>
<ContentControl prism:RegionManager.RegionName="{x:Static region:RegionNames.LoginContentRegion}" Margin="5"/>
</Grid>2.注册导航#
App.cs：
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protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.Register<IMedicineSerivce, MedicineSerivce>();
containerRegistry.Register<IPatientService, PatientService>();
containerRegistry.Register<IUserService, UserService>();
//注册全局命令
containerRegistry.RegisterSingleton<IApplicationCommands, ApplicationCommands>();
containerRegistry.RegisterInstance<IFlyoutService>(Container.Resolve<FlyoutService>());
//注册导航
containerRegistry.RegisterForNavigation<LoginMainContent>();
containerRegistry.RegisterForNavigation<CreateAccount>();}
3.区域导航#
LoginWindowViewModel.cs：
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public class LoginWindowViewModel:BindableBase
{
private readonly IRegionManager _regionManager;
private readonly IUserService _userService;
private DelegateCommand _loginLoadingCommand;
public DelegateCommand LoginLoadingCommand =>
_loginLoadingCommand ?? (_loginLoadingCommand = new DelegateCommand(ExecuteLoginLoadingCommand));
void ExecuteLoginLoadingCommand()
{
//在LoginContentRegion区域导航到LoginMainContent
_regionManager.RequestNavigate(RegionNames.LoginContentRegion, "LoginMainContent");
Global.AllUsers = _userService.GetAllUsers();
}
public LoginWindowViewModel(IRegionManager regionManager, IUserService userService)
{
_regionManager = regionManager;
_userService = userService;
}
}
LoginMainContentViewModel.cs：
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public class LoginMainContentViewModel : BindableBase
{
private readonly IRegionManager _regionManager;
private DelegateCommand _createAccountCommand;
public DelegateCommand CreateAccountCommand =>
_createAccountCommand ?? (_createAccountCommand = new DelegateCommand(ExecuteCreateAccountCommand));
//导航到CreateAccount
void ExecuteCreateAccountCommand()
{
Navigate("CreateAccount");
}
private void Navigate(string navigatePath)
{
if (navigatePath != null)
_regionManager.RequestNavigate(RegionNames.LoginContentRegion, navigatePath);
}
public LoginMainContentViewModel(IRegionManager regionManager)
{
_regionManager = regionManager;
}
}
效果如下：
这里我们可以看到我们调用RegionMannager的RequestNavigate方法，其实这样看不能很好的说明是基于区域的做法，如果将换成下面的写法可能更好理解一点：
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//在LoginContentRegion区域导航到LoginMainContent
_regionManager.RequestNavigate(RegionNames.LoginContentRegion, "LoginMainContent");
换成
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//在LoginContentRegion区域导航到LoginMainContent
IRegion region = _regionManager.Regions[RegionNames.LoginContentRegion];
region.RequestNavigate("LoginMainContent");
其实RegionMannager的RequestNavigate源码也是大概实现也是大概如此，就是去调Region的RequestNavigate的方法，而Region的导航是实现了一个INavigateAsync接口：
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public interface INavigateAsync
{
void RequestNavigate(Uri target, Action navigationCallback);
void RequestNavigate(Uri target, Action navigationCallback, NavigationParameters navigationParameters);
}
我们可以看到有RequestNavigate方法三个形参：
target：表示将要导航的页面Uri
navigationCallback:导航后的回调方法
navigationParameters:导航传递参数(下面会详解)
那么我们将上述加上回调方法：
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//在LoginContentRegion区域导航到LoginMainContent
IRegion region = _regionManager.Regions[RegionNames.LoginContentRegion];
region.RequestNavigate("LoginMainContent", NavigationCompelted);
private void NavigationCompelted(NavigationResult result)
{
if (result.Result==true)
{
MessageBox.Show("导航到LoginMainContent页面成功");
}
else
{
MessageBox.Show("导航到LoginMainContent页面失败");
}}
效果如下：
二.View和ViewModel参与导航过程#
1.INavigationAware#
我们经常在两个页面之间导航需要处理一些逻辑，例如，LoginMainContent页面导航到CreateAccount页面时候，LoginMainContent退出页面的时刻要保存页面数据，导航到CreateAccount页面的时刻处理逻辑(例如获取从LoginMainContent页面的信息)，Prism的导航系统通过一个INavigationAware接口：
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public interface INavigationAware : Object
{
Void OnNavigatedTo(NavigationContext navigationContext);
Boolean IsNavigationTarget(NavigationContext navigationContext);
Void OnNavigatedFrom(NavigationContext navigationContext);
}OnNavigatedFrom：导航之前触发,一般用于保存该页面的数据
OnNavigatedTo：导航后目的页面触发，一般用于初始化或者接受上页面的传递参数
IsNavigationTarget：True则重用该View实例，Flase则每一次导航到该页面都会实例化一次
我们用代码来演示这三个方法：
LoginMainContentViewModel.cs：
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public class LoginMainContentViewModel : BindableBase, INavigationAware
{
private readonly IRegionManager _regionManager;
private DelegateCommand _createAccountCommand;
public DelegateCommand CreateAccountCommand =>
_createAccountCommand ?? (_createAccountCommand = new DelegateCommand(ExecuteCreateAccountCommand));
void ExecuteCreateAccountCommand()
{
Navigate("CreateAccount");
}
private void Navigate(string navigatePath)
{
if (navigatePath != null)
_regionManager.RequestNavigate(RegionNames.LoginContentRegion, navigatePath);
}
public LoginMainContentViewModel(IRegionManager regionManager)
{
_regionManager = regionManager;
}
public bool IsNavigationTarget(NavigationContext navigationContext)
{
return true;
}
public void OnNavigatedFrom(NavigationContext navigationContext)
{
MessageBox.Show("退出了LoginMainContent");
}
public void OnNavigatedTo(NavigationContext navigationContext)
{
MessageBox.Show("从CreateAccount导航到LoginMainContent");
}}
CreateAccountViewModel.cs:
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public class CreateAccountViewModel : BindableBase,INavigationAware
{
private DelegateCommand _loginMainContentCommand;
public DelegateCommand LoginMainContentCommand =>
_loginMainContentCommand ?? (_loginMainContentCommand = new DelegateCommand(ExecuteLoginMainContentCommand));
void ExecuteLoginMainContentCommand()
{
Navigate("LoginMainContent");
}
public CreateAccountViewModel(IRegionManager regionManager)
{
_regionManager = regionManager;
}
private void Navigate(string navigatePath)
{
if (navigatePath != null)
_regionManager.RequestNavigate(RegionNames.LoginContentRegion, navigatePath);
}
public bool IsNavigationTarget(NavigationContext navigationContext)
{
return true;
}
public void OnNavigatedFrom(NavigationContext navigationContext)
{
MessageBox.Show("退出了CreateAccount");
}
public void OnNavigatedTo(NavigationContext navigationContext)
{
MessageBox.Show("从LoginMainContent导航到CreateAccount");
}
}
效果如下：
修改IsNavigationTarget为false：
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public class LoginMainContentViewModel : BindableBase, INavigationAware
{
public bool IsNavigationTarget(NavigationContext navigationContext)
{
return false;
}}
public class CreateAccountViewModel : BindableBase,INavigationAware
{
public bool IsNavigationTarget(NavigationContext navigationContext)
{
return false;
}}
效果如下:
我们会发现LoginMainContent和CreateAccount页面的数据不见了，这是因为第二次导航到页面的时候当IsNavigationTarget为false时，View将会重新实例化，导致ViewModel也重新加载,因此所有数据都清空了
2.IRegionMemberLifetime#
同时，Prism还可以通过IRegionMemberLifetime接口的KeepAlive布尔属性控制区域的视图的生命周期,我们在上一篇关于区域管理器说到，当视图添加到区域时候，像ContentControl这种单独显示一个活动视图，可以通过Region的Activate和Deactivate方法激活和失效视图，像ItemsControl这种可以同时显示多个活动视图的，可以通过Region的Add和Remove方法控制增加活动视图和失效视图，而当视图的KeepAlive为false，Region的Activate另外一个视图时，则该视图的实例则会去除出区域，为什么我们不在区域管理器讲解该接口呢？因为当导航的时候，同样的是在触发了Region的Activate和Deactivate，当有IRegionMemberLifetime接口时则会触发Region的Add和Remove方法，这里可以去看下Prism的RegionMemberLifetimeBehavior源码
我们将LoginMainContentViewModel实现IRegionMemberLifetime接口，并且把KeepAlive设置为false，同样的将IsNavigationTarget设置为true
LoginMainContentViewModel.cs:
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public class LoginMainContentViewModel : BindableBase, INavigationAware，IRegionMemberLifetime
{
public bool KeepAlive => false;
private readonly IRegionManager _regionManager;
private DelegateCommand _createAccountCommand;
public DelegateCommand CreateAccountCommand =>
_createAccountCommand ?? (_createAccountCommand = new DelegateCommand(ExecuteCreateAccountCommand));
void ExecuteCreateAccountCommand()
{
Navigate("CreateAccount");
}
private void Navigate(string navigatePath)
{
if (navigatePath != null)
_regionManager.RequestNavigate(RegionNames.LoginContentRegion, navigatePath);
}
public LoginMainContentViewModel(IRegionManager regionManager)
{
_regionManager = regionManager;
}
public bool IsNavigationTarget(NavigationContext navigationContext)
{
return true;
}
public void OnNavigatedFrom(NavigationContext navigationContext)
{
MessageBox.Show("退出了LoginMainContent");
}
public void OnNavigatedTo(NavigationContext navigationContext)
{
MessageBox.Show("从CreateAccount导航到LoginMainContent");
}}
效果如下：
我们会发现跟没实现IRegionMemberLifetime接口和IsNavigationTarget设置为false情况一样，当KeepAlive为false时，通过断点知道，重新导航回LoginMainContent页面时不会触发IsNavigationTarget方法，因此可以
知道判断顺序是：KeepAlive -->IsNavigationTarget
3.IConfirmNavigationRequest#
Prism的导航系统还支持再导航前允许是否需要导航的交互需求，这里我们在CreateAccount注册完用户后寻问是否需要导航回LoginMainContent页面，代码如下：
CreateAccountViewModel.cs:
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public class CreateAccountViewModel : BindableBase, INavigationAware，IConfirmNavigationRequest
{
private DelegateCommand _loginMainContentCommand;
public DelegateCommand LoginMainContentCommand =>
_loginMainContentCommand ?? (_loginMainContentCommand = new DelegateCommand(ExecuteLoginMainContentCommand));
private DelegateCommand<object> _verityCommand;
public DelegateCommand<object> VerityCommand =>
_verityCommand ?? (_verityCommand = new DelegateCommand<object>(ExecuteVerityCommand));
void ExecuteLoginMainContentCommand()
{
Navigate("LoginMainContent");
}
public CreateAccountViewModel(IRegionManager regionManager)
{
_regionManager = regionManager;
}
private void Navigate(string navigatePath)
{
if (navigatePath != null)
_regionManager.RequestNavigate(RegionNames.LoginContentRegion, navigatePath);
}
public bool IsNavigationTarget(NavigationContext navigationContext)
{
return true;
}
public void OnNavigatedFrom(NavigationContext navigationContext)
{
MessageBox.Show("退出了CreateAccount");
}
public void OnNavigatedTo(NavigationContext navigationContext)
{
MessageBox.Show("从LoginMainContent导航到CreateAccount");
}
//注册账号
void ExecuteVerityCommand(object parameter)
{
if (!VerityRegister(parameter))
{
return;
}
MessageBox.Show("注册成功!");
LoginMainContentCommand.Execute();
}
//导航前询问
public void ConfirmNavigationRequest(NavigationContext navigationContext, Action<bool> continuationCallback)
{
var result = false;
if (MessageBox.Show("是否需要导航到LoginMainContent页面?", "Naviagte?",MessageBoxButton.YesNo) ==MessageBoxResult.Yes)
{
result = true;
}
continuationCallback(result);
}}
效果如下：
三.导航期间传递参数#
Prism提供NavigationParameters类以帮助指定和检索导航参数，在导航期间，可以通过访问以下方法来传递导航参数：
INavigationAware接口的IsNavigationTarget，OnNavigatedFrom和OnNavigatedTo方法中IsNavigationTarget，OnNavigatedFrom和OnNavigatedTo中形参NavigationContext对象的NavigationParameters属性
IConfirmNavigationRequest接口的ConfirmNavigationRequest形参NavigationContext对象的NavigationParameters属性
区域导航的INavigateAsync接口的RequestNavigate方法赋值给其形参navigationParameters
导航日志IRegionNavigationJournal接口CurrentEntry属性的NavigationParameters类型的Parameters属性(下面会介绍导航日志)
这里我们CreateAccount页面注册完用户后询问是否需要用当前注册用户来作为登录LoginId，来演示传递导航参数，代码如下：
CreateAccountViewModel.cs(修改代码部分):
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private string _registeredLoginId;
public string RegisteredLoginId
{
get { return _registeredLoginId; }
set { SetProperty(ref _registeredLoginId, value); }}
public bool IsUseRequest { get; set; }
void ExecuteVerityCommand(object parameter)
{
if (!VerityRegister(parameter))
{
return;
}
this.IsUseRequest = true;
MessageBox.Show("注册成功!");
LoginMainContentCommand.Execute();}
public void ConfirmNavigationRequest(NavigationContext navigationContext, Action continuationCallback)
{
if (!string.IsNullOrEmpty(RegisteredLoginId) && this.IsUseRequest)
{
if (MessageBox.Show("是否需要用当前注册的用户登录?", "Naviagte?", MessageBoxButton.YesNo) == MessageBoxResult.Yes)
{
navigationContext.Parameters.Add("loginId", RegisteredLoginId);
}
}
continuationCallback(true);}
LoginMainContentViewModel.cs(修改代码部分):
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public void OnNavigatedTo(NavigationContext navigationContext)
{
MessageBox.Show("从CreateAccount导航到LoginMainContent");
var loginId= navigationContext.Parameters["loginId"] as string;
if (loginId!=null)
{
this.CurrentUser = new User() { LoginId=loginId};
}
}
效果如下：
四.导航日志#
Prism导航系统同样的和WPF导航系统一样，都支持导航日志，Prism是通过IRegionNavigationJournal接口来提供区域导航日志功能，
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public interface IRegionNavigationJournal
{
bool CanGoBack { get; }
bool CanGoForward { get; }
IRegionNavigationJournalEntry CurrentEntry {get;}
INavigateAsync NavigationTarget { get; set; }
void GoBack();
void GoForward();
void RecordNavigation(IRegionNavigationJournalEntry entry, bool persistInHistory);
void Clear();
}我们将在登录界面接入导航日志功能,代码如下:
LoginMainContent.xaml(前进箭头代码部分):
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<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseLeftButtonDown">
<i:InvokeCommandAction Command="{Binding GoForwardCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" Value="#F9F9F9"/>
</Trigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
BoolToVisibilityConverter.cs:
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public class BoolToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value==null)
{
return DependencyProperty.UnsetValue;
}
var isCanExcute = (bool)value;
if (isCanExcute)
{
return Visibility.Visible;
}
else
{
return Visibility.Hidden;
}
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}}
LoginMainContentViewModel.cs(修改代码部分):
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IRegionNavigationJournal _journal;
private DelegateCommand _loginCommand;
public DelegateCommand LoginCommand =>
_loginCommand ?? (_loginCommand = new DelegateCommand<PasswordBox>(ExecuteLoginCommand, CanExecuteGoForwardCommand));
private DelegateCommand _goForwardCommand;
public DelegateCommand GoForwardCommand =>
_goForwardCommand ?? (_goForwardCommand = new DelegateCommand(ExecuteGoForwardCommand));
private void ExecuteGoForwardCommand()
{
_journal.GoForward();}
private bool CanExecuteGoForwardCommand(PasswordBox passwordBox)
{
this.IsCanExcute=_journal != null && _journal.CanGoForward;
return true;}
public void OnNavigatedTo(NavigationContext navigationContext)
{
//MessageBox.Show("从CreateAccount导航到LoginMainContent");
_journal = navigationContext.NavigationService.Journal;
var loginId= navigationContext.Parameters["loginId"] as string;
if (loginId!=null)
{
this.CurrentUser = new User() { LoginId=loginId};
}
LoginCommand.RaiseCanExecuteChanged();}
CreateAccountViewModel.cs(修改代码部分):
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IRegionNavigationJournal _journal;
private DelegateCommand _goBackCommand;
public DelegateCommand GoBackCommand =>
_goBackCommand ?? (_goBackCommand = new DelegateCommand(ExecuteGoBackCommand));
void ExecuteGoBackCommand()
{
_journal.GoBack();}
public void OnNavigatedTo(NavigationContext navigationContext)
{
//MessageBox.Show("从LoginMainContent导航到CreateAccount");
_journal = navigationContext.NavigationService.Journal;}
效果如下：
选择退出导航日志#
如果不打算将页面在导航过程中不加入导航日志，例如LoginMainContent页面，可以通过实现IJournalAware并从PersistInHistory（）返回false
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public class LoginMainContentViewModel : IJournalAware
{
public bool PersistInHistory() => false;
} 五.小结：#
prism的导航系统可以跟wpf导航并行使用，这是prism官方文档也支持的，因为prism的导航系统是基于区域的，不依赖于wpf，不过更推荐于单独使用prism的导航系统，因为在MVVM模式下更灵活，支持依赖注入,通过区域管理器能够更好的管理视图View,更能适应复杂应用程序需求，wpf导航系统不支持依赖注入模式，也依赖于Frame元素，而且在导航过程中也是容易强依赖View部分，下一篇将会讲解Prism的对话框服务
六.源码#
最后，附上整个demo的源代码：PrismDemo源码
作者： RyzenAdorer
