给一些MVVM中的视图命令

Question

让我们想象我有一些用户控制。用户控件有一些子窗口。而用户控制用户想要关闭某种类型的子窗口。有一个在后面的用户控件代码的方法：

public void CloseChildWindows(ChildWindowType type) 
{ 
    ... 
} 

但我不能调用此方法，因为我没有看法的直接访问。

我想到的另一个解决方案是以某种方式将用户控件ViewModel作为其属性之一（这样我可以将它绑定并直接给ViewModel）。但我不希望用户控制用户知道关于用户控件ViewModel的任何信息。

那么解决这个问题的正确方法是什么？实现这一

Answer 1

一种方式是对视图模型来请求子窗口应关闭：

public class ExampleUserControl_ViewModel 
{ 
    public Action ChildWindowsCloseRequested; 

    ... 
} 

那么该视图订阅视图模型的事件，并照顾关闭当它被解雇时的窗户。

public class ExampleUserControl : UserControl 
{ 
    public ExampleUserControl() 
    { 
     var viewModel = new ExampleUserControl_ViewModel(); 
     viewModel.ChildWindowsCloseRequested += OnChildWindowsCloseRequested; 

     DataContext = viewModel; 
    } 

    private void OnChildWindowsCloseRequested() 
    { 
     // ... close child windows 
    } 

    ... 
} 

所以这里的视图模型可以确保子窗口关闭，而没有任何视图的知识。

Answer 2

我已经把在WindowManager的概念，这是它的一个可怕名来处理这种情况在过去，让我们配对与WindowViewModel，仅略低于可怕的 - 但基本思路是：

public class WindowManager 
{ 
    public WindowManager() 
    { 
     VisibleWindows = new ObservableCollection<WindowViewModel>(); 
     VisibleWindows.CollectionChanged += OnVisibleWindowsChanged;    
    } 
    public ObservableCollection<WindowViewModel> VisibleWindows {get; private set;} 
    private void OnVisibleWindowsChanged(object sender, NotifyCollectionChangedEventArgs args) 
    { 
     // process changes, close any removed windows, open any added windows, etc. 
    } 
} 

public class WindowViewModel : INotifyPropertyChanged 
{ 
    private bool _isOpen; 
    private WindowManager _manager; 
    public WindowViewModel(WindowManager manager) 
    { 
     _manager = manager; 
    } 
    public bool IsOpen 
    { 
     get { return _isOpen; } 
     set 
     { 
      if(_isOpen && !value) 
      { 
       _manager.VisibleWindows.Remove(this); 
      } 
      if(value && !_isOpen) 
      { 
       _manager.VisibleWindows.Add(this); 
      } 
      _isOpen = value; 
      OnPropertyChanged("IsOpen"); 
     } 
    }  

    public event PropertyChangedEventHandler PropertyChanged = delegate {}; 
    private void OnPropertyChanged(string name) 
    { 
     PropertyChanged(this, new PropertyChangedEventArgs(name)); 
    } 
} 

注：我只是非常随意地把它扔在一起;你当然想调整这个想法，以满足你的特定需求。

但是无论如何，基本前提是您的命令可以在WindowViewModel对象上工作，适当地切换IsOpen标志，并且管理器类处理打开/关闭任何新窗口。有几十个可能的方式来做到这一点，但它在紧要关头为我工作在过去（当实际执行和我的手机上扔在一起，这是）

Answer 3

我觉得我只是找到了一个相当不错的MVVM解决这个问题。我写了一个暴露类型属性WindowType和布尔属性Open的行为。 DataBinding后者允许ViewModel轻松打开和关闭窗口，而无需了解任何有关View的内容。

得到爱的行为...:)

的Xaml：

<UserControl x:Class="WpfApplication1.OpenCloseWindowDemo" 
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
      xmlns:local="clr-namespace:WpfApplication1" 
      xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" 
      mc:Ignorable="d" 
      d:DesignHeight="300" d:DesignWidth="300"> 

    <UserControl.DataContext> 
     <local:ViewModel /> 
    </UserControl.DataContext> 
    <i:Interaction.Behaviors> 
     <!-- TwoWay binding is necessary, otherwise after user closed a window directly, it cannot be opened again --> 
     <local:OpenCloseWindowBehavior WindowType="local:BlackWindow" Open="{Binding BlackOpen, Mode=TwoWay}" /> 
     <local:OpenCloseWindowBehavior WindowType="local:YellowWindow" Open="{Binding YellowOpen, Mode=TwoWay}" /> 
     <local:OpenCloseWindowBehavior WindowType="local:PurpleWindow" Open="{Binding PurpleOpen, Mode=TwoWay}" /> 
    </i:Interaction.Behaviors> 
    <UserControl.Resources> 
     <Thickness x:Key="StdMargin">5</Thickness> 
     <Style TargetType="Button" > 
      <Setter Property="MinWidth" Value="60" /> 
      <Setter Property="Margin" Value="{StaticResource StdMargin}" /> 
     </Style> 
     <Style TargetType="Border" > 
      <Setter Property="Margin" Value="{StaticResource StdMargin}" /> 
     </Style> 
    </UserControl.Resources> 

    <Grid> 
     <StackPanel> 
      <StackPanel Orientation="Horizontal"> 
       <Border Background="Black" Width="30" /> 
       <Button Content="Open" Command="{Binding OpenBlackCommand}" CommandParameter="True" /> 
       <Button Content="Close" Command="{Binding OpenBlackCommand}" CommandParameter="False" /> 
      </StackPanel> 
      <StackPanel Orientation="Horizontal"> 
       <Border Background="Yellow" Width="30" /> 
       <Button Content="Open" Command="{Binding OpenYellowCommand}" CommandParameter="True" /> 
       <Button Content="Close" Command="{Binding OpenYellowCommand}" CommandParameter="False" /> 
      </StackPanel> 
      <StackPanel Orientation="Horizontal"> 
       <Border Background="Purple" Width="30" /> 
       <Button Content="Open" Command="{Binding OpenPurpleCommand}" CommandParameter="True" /> 
       <Button Content="Close" Command="{Binding OpenPurpleCommand}" CommandParameter="False" /> 
      </StackPanel> 
     </StackPanel> 
    </Grid> 
</UserControl> 

YellowWindow（黑色/紫色一样）：

<Window x:Class="WpfApplication1.YellowWindow" 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
     Title="YellowWindow" Height="300" Width="300"> 
    <Grid Background="Yellow" /> 
</Window> 

视图模型，ActionCommand：

using System; 
using System.ComponentModel; 
using System.Windows.Input; 

namespace WpfApplication1 
{ 
    public class ViewModel : INotifyPropertyChanged 
    { 
     public event PropertyChangedEventHandler PropertyChanged; 
     private void OnPropertyChanged(string propertyName) 
     { 
      if (this.PropertyChanged != null) 
       PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); 
     } 

     private bool _blackOpen; 
     public bool BlackOpen { get { return _blackOpen; } set { _blackOpen = value; OnPropertyChanged("BlackOpen"); } } 

     private bool _yellowOpen; 
     public bool YellowOpen { get { return _yellowOpen; } set { _yellowOpen = value; OnPropertyChanged("YellowOpen"); } } 

     private bool _purpleOpen; 
     public bool PurpleOpen { get { return _purpleOpen; } set { _purpleOpen = value; OnPropertyChanged("PurpleOpen"); } } 

     public ICommand OpenBlackCommand { get; private set; } 
     public ICommand OpenYellowCommand { get; private set; } 
     public ICommand OpenPurpleCommand { get; private set; } 


     public ViewModel() 
     { 
      this.OpenBlackCommand = new ActionCommand<bool>(OpenBlack); 
      this.OpenYellowCommand = new ActionCommand<bool>(OpenYellow); 
      this.OpenPurpleCommand = new ActionCommand<bool>(OpenPurple); 
     } 

     private void OpenBlack(bool open) { this.BlackOpen = open; } 
     private void OpenYellow(bool open) { this.YellowOpen = open; } 
     private void OpenPurple(bool open) { this.PurpleOpen = open; } 

    } 

    public class ActionCommand<T> : ICommand 
    { 
     public event EventHandler CanExecuteChanged; 
     private Action<T> _action; 

     public ActionCommand(Action<T> action) 
     { 
      _action = action; 
     } 

     public bool CanExecute(object parameter) { return true; } 

     public void Execute(object parameter) 
     { 
      if (_action != null) 
      { 
       var castParameter = (T)Convert.ChangeType(parameter, typeof(T)); 
       _action(castParameter); 
      } 
     } 
    } 
} 

打开CloseWindowBehavior：

using System; 
using System.Windows; 
using System.Windows.Controls; 
using System.Windows.Interactivity; 

namespace WpfApplication1 
{ 
    public class OpenCloseWindowBehavior : Behavior<UserControl> 
    { 
     private Window _windowInstance; 

     public Type WindowType { get { return (Type)GetValue(WindowTypeProperty); } set { SetValue(WindowTypeProperty, value); } } 
     public static readonly DependencyProperty WindowTypeProperty = DependencyProperty.Register("WindowType", typeof(Type), typeof(OpenCloseWindowBehavior), new PropertyMetadata(null)); 

     public bool Open { get { return (bool)GetValue(OpenProperty); } set { SetValue(OpenProperty, value); } } 
     public static readonly DependencyProperty OpenProperty = DependencyProperty.Register("Open", typeof(bool), typeof(OpenCloseWindowBehavior), new PropertyMetadata(false, OnOpenChanged)); 

     /// <summary> 
     /// Opens or closes a window of type 'WindowType'. 
     /// </summary> 
     private static void OnOpenChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) 
     { 
      var me = (OpenCloseWindowBehavior)d; 
      if ((bool)e.NewValue) 
      { 
       object instance = Activator.CreateInstance(me.WindowType); 
       if (instance is Window) 
       { 
        Window window = (Window)instance; 
        window.Closing += (s, ev) => 
        { 
         if (me.Open) // window closed directly by user 
         { 
          me._windowInstance = null; // prevents repeated Close call 
          me.Open = false; // set to false, so next time Open is set to true, OnOpenChanged is triggered again 
         } 
        }; 
        window.Show(); 
        me._windowInstance = window; 
       } 
       else 
       { 
        // could check this already in PropertyChangedCallback of WindowType - but doesn't matter until someone actually tries to open it. 
        throw new ArgumentException(string.Format("Type '{0}' does not derive from System.Windows.Window.", me.WindowType)); 
       } 
      } 
      else 
      { 
       if (me._windowInstance != null) 
        me._windowInstance.Close(); // closed by viewmodel 
      } 
     } 
    } 
} 

Answer 4

纯粹主义者的合理方式是创建一个处理导航的服务。简短摘要：创建NavigationService，在NavigationService上注册您的视图，并使用视图模型内的NavigationService进行导航。

实施例：

class NavigationService 
{ 
    private Window _a; 

    public void RegisterViewA(Window a) { _a = a; } 

    public void CloseWindowA() { a.Close(); } 
} 

要得到的NavigationService你一个参考可以使在其顶部（即INavigationService）的抽象和寄存器/经由的IoC得到它。更恰当地说，你甚至可以做两个抽象，一个包含注册方法（由视图使用）和一个包含执行器（由视图模型使用）的抽象。

对于您可以检查出吉尔Cleeren实施这在很大程度上依赖于国际奥委会更详细的例子：

http://www.silverlightshow.net/video/Applied-MVVM-in-Win8-Webinar.aspx开始〇时36分30秒

Answer 5

大多数回答这个问题涉及到一个状态变量。由ViewModel控制，并且View对这个变量进行更改。这对于打开或关闭一个窗口，或者只是显示或隐藏某些控件而言是有用的，如有状态命令。尽管如此，它对无状态事件命令不起作用。您可能会在信号的上升沿触发一些操作，但需要再次将信号设置为低（错误），否则将不再触发。

我写了一篇关于ViewCommand pattern的文章，它解决了这个问题。它基本上是从视图到当前ViewModel的常规命令的反向。它涉及一个接口，每个ViewModel都可以实现向所有当前连接的视图发送命令。当DataContext属性更改时，可以扩展View以注册每个分配的ViewModel。此注册将视图添加到ViewModel中的视图列表。每当ViewModel需要在View中运行命令时，它会遍历所有已注册的视图并在其上运行该命令（如果存在）。这使用反射来查找View类中的ViewCommand方法，但在相反的方向上也是如此。

的ViewCommand方法在视图类：

public partial class TextItemView : UserControl 
{ 
    [ViewCommand] 
    public void FocusText() 
    { 
     MyTextBox.Focus(); 
    } 
} 

这是从一个视图模型称为：

private void OnAddText() 
{ 
    ViewCommandManager.Invoke("FocusText"); 
} 

的文章可以on my website和旧版本on CodeProject。

包含的代码（BSD许可证）提供了一些措施，以允许在代码混淆期间重命名方法。