.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git

在讲解Prism导航系统以前，咱们先来看看一个例子,我在以前的demo项目建立一个登陆界面：github

 

咱们看到这里是否是一开始想象到使用WPF带有的导航系统，经过Frame和Page进行页面跳转，而后经过导航日志的GoBack和GoForward实现后退和前进，其实这是经过使用Prism的导航框架实现的,下面咱们来看看如何在Prism的MVVM模式下实现该功能express

一.区域导航
咱们在上一篇介绍了Prism的区域管理，而Prism的导航系统也是基于区域的，首先咱们来看看如何在区域导航c#

1.注册区域
LoginWindow.xaml：app

<Window x:Class="PrismMetroSample.Shell.Views.Login.LoginWindow"
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>
</Window>
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2.注册导航
App.cs：框架

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>();
}
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3.区域导航
LoginWindowViewModel.cs：ide

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;
}

}
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LoginMainContentViewModel.cs：this

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;
}

}
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效果以下：spa

 

这里咱们能够看到咱们调用RegionMannager的RequestNavigate方法，其实这样看不能很好的说明是基于区域的作法，若是将换成下面的写法可能更好理解一点：3d

//在LoginContentRegion区域导航到LoginMainContent
_regionManager.RequestNavigate(RegionNames.LoginContentRegion, "LoginMainContent");
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换成

//在LoginContentRegion区域导航到LoginMainContent
IRegion region = _regionManager.Regions[RegionNames.LoginContentRegion];
region.RequestNavigate("LoginMainContent");
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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：

public interface INavigateAsync
{
void RequestNavigate(Uri target, Action<NavigationResult> navigationCallback);
void RequestNavigate(Uri target, Action<NavigationResult> navigationCallback, NavigationParameters navigationParameters);

}
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咱们能够看到有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)
那么咱们将上述加上回调方法：

//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");
}
}
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效果以下：

 

二.View和ViewModel参与导航过程
1.INavigationAware
咱们常常在两个页面之间导航须要处理一些逻辑，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的导航系统经过一个INavigationAware接口：

public interface INavigationAware : Object
{
Void OnNavigatedTo(NavigationContext navigationContext);

Boolean IsNavigationTarget(NavigationContext navigationContext);

Void OnNavigatedFrom(NavigationContext navigationContext);
}
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OnNavigatedFrom：导航以前触发,通常用于保存该页面的数据
OnNavigatedTo：导航后目的页面触发，通常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
咱们用代码来演示这三个方法：

LoginMainContentViewModel.cs：

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");
}
}
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CreateAccountViewModel.cs:

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");
}

}
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效果以下：

 

修改IsNavigationTarget为false：

public class LoginMainContentViewModel : BindableBase, INavigationAware
{
public bool IsNavigationTarget(NavigationContext navigationContext)
{
return false;
}
}

public class CreateAccountViewModel : BindableBase,INavigationAware
{
public bool IsNavigationTarget(NavigationContext navigationContext)
{
return false;
}
}
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效果以下:

 

咱们会发现LoginMainContent和CreateAccount页面的数据不见了，这是由于第二次导航到页面的时候当IsNavigationTarget为false时，View将会从新实例化，致使ViewModel也从新加载,所以全部数据都清空了

2.IRegionMemberLifetime
同时，Prism还能够经过IRegionMemberLifetime接口的KeepAlive布尔属性控制区域的视图的生命周期,咱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，能够经过Region的Activate和Deactivate方法激活和失效视图，像ItemsControl这种能够同时显示多个活动视图的，能够经过Region的Add和Remove方法控制增长活动视图和失效视图，而当视图的KeepAlive为false，Region的Activate另一个视图时，则该视图的实例则会去除出区域，为何咱们不在区域管理器讲解该接口呢？由于当导航的时候，一样的是在触发了Region的Activate和Deactivate，当有IRegionMemberLifetime接口时则会触发Region的Add和Remove方法，这里能够去看下Prism的RegionMemberLifetimeBehavior源码

咱们将LoginMainContentViewModel实现IRegionMemberLifetime接口，而且把KeepAlive设置为false，一样的将IsNavigationTarget设置为true

LoginMainContentViewModel.cs:

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");
}
}
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效果以下：

 

咱们会发现跟没实现IRegionMemberLifetime接口和IsNavigationTarget设置为false状况同样，当KeepAlive为false时，经过断点知道，从新导航回LoginMainContent页面时不会触发IsNavigationTarget方法，所以能够

知道判断顺序是：KeepAlive -->IsNavigationTarget

3.IConfirmNavigationRequest
Prism的导航系统还支持再导航前容许是否须要导航的交互需求，这里咱们在CreateAccount注册完用户后寻问是否须要导航回LoginMainContent页面，代码以下：

CreateAccountViewModel.cs:

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");
}

//注册帐号
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("是否须要导航到LoginMainContent页面?", "Naviagte?",MessageBoxButton.YesNo) ==MessageBoxResult.Yes)
{
result = true;
}
continuationCallback(result);
}
}
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效果以下：

 

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，能够经过访问如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)
这里咱们CreateAccount页面注册完用户后询问是否须要用当前注册用户来做为登陆LoginId，来演示传递导航参数，代码以下：

CreateAccountViewModel.cs(修改代码部分):

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<bool> continuationCallback)
{
if (!string.IsNullOrEmpty(RegisteredLoginId) && this.IsUseRequest)
{
if (MessageBox.Show("是否须要用当前注册的用户登陆?", "Naviagte?", MessageBoxButton.YesNo) == MessageBoxResult.Yes)
{
navigationContext.Parameters.Add("loginId", RegisteredLoginId);
}
}
continuationCallback(true);
}
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LoginMainContentViewModel.cs(修改代码部分):

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};
}

}
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效果以下：

 

四.导航日志
Prism导航系统一样的和WPF导航系统同样，都支持导航日志，Prism是经过IRegionNavigationJournal接口来提供区域导航日志功能，

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();
}
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咱们将在登陆界面接入导航日志功能,代码以下:

LoginMainContent.xaml(前进箭头代码部分):

<TextBlock Width="30" Height="30" HorizontalAlignment="Right" Text="" FontWeight="Bold" FontFamily="pack://application:,,,/PrismMetroSample.Infrastructure;Component/Assets/Fonts/#iconfont" FontSize="30" Margin="10" Visibility="{Binding IsCanExcute,Converter={StaticResource boolToVisibilityConverter}}">
<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>
</TextBlock>
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BoolToVisibilityConverter.cs:

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();
}
}
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LoginMainContentViewModel.cs(修改代码部分):

IRegionNavigationJournal _journal;

private DelegateCommand<PasswordBox> _loginCommand;
public DelegateCommand<PasswordBox> 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();
}
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CreateAccountViewModel.cs(修改代码部分):

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;
}
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效果以下：

 

选择退出导航日志
若是不打算将页面在导航过程当中不加入导航日志，例如LoginMainContent页面，能够经过实现IJournalAware并从PersistInHistory（）返回false

public class LoginMainContentViewModel : IJournalAware
{
public bool PersistInHistory() => false;
}
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五.小结：
prism的导航系统能够跟wpf导航并行使用，这是prism官方文档也支持的，由于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，由于在MVVM模式下更灵活，支持依赖注入,经过区域管理器可以更好的管理视图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，并且在导航过程当中也是容易强依赖View部分，下一篇将会讲解Prism的对话框服务

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.NET Core 3 WPF MVVM框架 Prism系列之导航系统
https://blog.51cto.com/u_4018548/6421075