给出一些在MVVM中查看的命令
给出一些在MVVM中查看的命令
提问于 2013-03-18 03:25:01
让我们假设我有一些用户控制。用户控件有一些子窗口。并且用户控件用户想要关闭某种类型的子窗口。在用户控件代码后面有一个方法：
public void CloseChildWindows(ChildWindowType type)
{
...
}但是我不能调用这个方法，因为我不能直接访问视图。
我考虑的另一个解决方案是以某种方式将用户控件ViewModel公开为其属性之一(这样我就可以绑定它并直接向ViewModel发出命令)。但是我不想让用户控件用户知道任何关于用户控件ViewModel的事情。
那么解决这个问题的正确方法是什么呢？
回答 5
Stack Overflow用户
发布于 2013-03-20 08:14:51
我觉得我找到了一个很好的MVVM解决方案。我编写了一个行为，它公开了一个类型属性WindowType和一个布尔属性Open。DataBinding后者允许ViewModel轻松地打开和关闭窗口，而无需了解有关视图的任何信息。
爱的行为..。:)
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)：
<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
}
}
}
}Stack Overflow用户
发布于 2013-03-20 04:12:25
我过去曾通过引入WindowManager的概念来处理这种情况，这对它来说是一个可怕的名称，所以让我们将它与WindowViewModel配对，它只是稍微不那么可怕-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));
}
}注意:我只是非常随意地把这些放在一起；您当然会希望根据您的特定需求来调整这个想法。
但不管是谁，基本的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manager类处理打开/关闭任何新窗口。有几十种可能的方法可以做到这一点，但它在过去的紧要关头对我来说是有效的(当实际实现时，而不是在我的手机上一起使用时)
Stack Overflow用户
发布于 2013-03-21 21:10:22
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。简要总结:创建一个NavigationService，在NavigationService上注册您的视图，并使用视图模型中的NavigationService进行导航。
示例：
class NavigationService
{
private Window _a;
public void RegisterViewA(Window a) { _a = a; }
public void CloseWindowA() { a.Close(); }
}要获得对NavigationService的引用，您可以在其之上进行抽象(即INavigationService)，并通过IoC注册/获取它。更确切地说，您甚至可以创建两个抽象，一个包含注册方法(由视图使用)，另一个包含执行器(由视图模型使用)。
有关更详细的示例，您可以查看Gill Cleeren的实现，它严重依赖于IoC：
http://www.silverlightshow.net/video/Applied-MVVM-in-Win8-Webinar.aspx从00:36:30开始
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/15465161
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