让我们想象一下，我有一个用户控件。这个用户控件有一些子窗口。用户希望关闭某种类型的子窗口。在用户控件的代码后台有一个方法：
public void CloseChildWindows(ChildWindowType type)
{
...
}
但是我无法调用这个方法，因为我没有直接访问视图的权限。
我想到的另一个解决方案是以某种方式公开用户控制ViewModel作为其属性之一（这样我就可以绑定它并直接将命令传递给ViewModel）。但是我不希望用户控制的用户知道任何关于用户控制的ViewModel的信息。
那么，解决这个问题的正确方法是什么？
WindowType和一个布尔属性Open。将后者数据绑定使得ViewModel可以轻松地打开和关闭窗口，而无需知道任何关于View的信息。
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>
黄窗口（黑/紫色相似）：
<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>
ViewModel, 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);
}
}
}
}
OpenCloseWindowBehavior:
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
}
}
}
}
我曾经通过引入一个名为WindowManager的概念来处理这种情况，这是一个非常糟糕的名称，因此我们将其与WindowViewModel配对，这个名称略微好些，但基本思想是：
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));
}
}
WindowViewModel对象上工作，适当地切换IsOpen标志，而管理器类处理打开/关闭任何新窗口。有数十种可能的方法来实现这一点，但在过去（当实际实现而不是在手机上拼凑时）对我来说已经足够了。对于纯粹主义者来说，一种合理的方式是创建一个处理导航的服务。简要概述：创建一个NavigationService，将您的视图注册到NavigationService，并在视图模型中使用NavigationService进行导航。
示例：
class NavigationService
{
private Window _a;
public void RegisterViewA(Window a) { _a = a; }
public void CloseWindowA() { a.Close(); }
}
实现这一点的一种方法是让视图模型请求关闭子窗口：
public class ExampleUserControl_ViewModel
{
public Action ChildWindowsCloseRequested;
...
}
public class ExampleUserControl : UserControl
{
public ExampleUserControl()
{
var viewModel = new ExampleUserControl_ViewModel();
viewModel.ChildWindowsCloseRequested += OnChildWindowsCloseRequested;
DataContext = viewModel;
}
private void OnChildWindowsCloseRequested()
{
// ... close child windows
}
...
}
我写了一篇关于ViewCommand模式的文章，它解决了这个问题。它基本上是正常命令的反向方向，正常命令从View到当前的ViewModel。它涉及到一个接口，每个ViewModel都可以实现该接口，向所有当前连接的View发送命令。当其DataContext属性更改时，可以扩展View以注册到每个分配的ViewModel。这个注册将View添加到ViewModel中的View列表中。每当ViewModel需要在View中运行命令时，它通过所有已注册的View，并在其中运行该命令（如果存在）。这利用了反射来查找View类中的ViewCommand方法，但双向绑定也是如此。
View类中的ViewCommand方法：
public partial class TextItemView : UserControl
{
[ViewCommand]
public void FocusText()
{
MyTextBox.Focus();
}
}
这是从ViewModel调用的：
private void OnAddText()
{
ViewCommandManager.Invoke("FocusText");
}
PlacementTarget（例如鼠标位置或相对于UIControl的左/右/上/下等）。或者您希望为Popup准备偏移量或其他技巧。在服务/信使方法中，这些必须作为服务的公共API中的参数公开，更不用说服务可能会被调用，例如从视图模型内部调用，而该视图模型对UI一无所知。（续） - Vector Sigmaobject，它应该是要分配的Window.Content。使用此答案的方法还可以让您简单地注册依赖属性，例如PlacementTarget（例如UIElement），突然之间，您可以在XAML中设置它（在那里所有UI信息都可用）。因此，您可以同时从ViewModel和UserControl设置内容！ - Vector Sigma