Question

我在mvvm

中遇到了中介模式的问题

我会描述几乎所有课程，以便更好地理解我的问题。

我得到了MainWindow和ViewModel，它非常简单，只是拿着我的一个UserControls，但是在ViewModel中有一个绑定到MainWindow中的ContentControl.Content的UserControl属性。
UserControls相同，每个只有一个按钮，另外还有两个带有处理clikcs命令的ViewModel。
Class Mediator是一个单例，我试图将它用于我的ViewModel之间的迭代

所以我要做的是在UserControls之间切换，而不是在MainWindowViewModel中创建它们和ViewModel。切换必须在我点击按钮后进行。例如，如果我单击FirstUserControl上的按钮，那么MainWindow的ContentControl应该切换到SecondUserControl。

问题出现在UserControlsViewModels中，我应该将UserControls对象作为Mediator NotifyCollegue（）函数中的参数传递，但我无法访问它们（当然，这是MVVM的原则之一），这就是用户类型的问题，因为标准类型应该不是问题（例如传递int或string ...）。

http://www.codeproject.com/Articles/35277/MVVM-Mediator-Pattern

为什么我不能在MainWindowViewModel中切换UserControls，因为我希望MainWindow能够清除除绑定到ContentControl的当前UserControl之外的所有内容。

这个问题的可能解决方案是什么，我应该创建另一个单一类并收集所有userControls引用并在UserControlsViewModels中使用它们，或者其他什么东西？

我希望我已经清楚地描述了我的问题，并且有某种解决方案。

我很乐意回答任何问题，非常感谢帮助!!!

再次感谢！

的MainView

<Window x:Class="TESTPROJECT.MainWindow"
    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:TESTPROJECT"
    mc:Ignorable="d"
    xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
    Title="MainWindow" Height="500" Width="750">



<Grid>
    <ContentControl Grid.Row="1" Content="{Binding PagesControl}"/>
</Grid>

MainView ViewModel

namespace TESTPROJECT
{
    class MainWindowViewModel : ViewModelBase
    {
        private UserControl _pagesControl;
        public UserControl PagesControl
        {
            //Property that switches UserControls
            set
            {
                _pagesControl = value;
                OnPropertyChanged();
            }
            get
            {
                return _pagesControl;
            }
        }

        public MainWindowViewModel()
        {
            //Method that will be listening all the changes from UserControls ViewModels
            Mediator.Instance.Register(
                (object obj) =>
                {
                    PagesControl = obj as UserControl;
                }, ViewModelMessages.UserWroteSomething);
        }
    }
}

FirstUserControl

<UserControl x:Class="TESTPROJECT.FirstUserControl"
         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:TESTPROJECT"
         xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">
<Grid>
    <Button Command="{Binding GetCommand}">
        hello, i'm first user control!
    </Button>
</Grid>

FirstUserControl ViewModel

namespace TESTPROJECT
{
class FirstUserControlViewModel : ViewModelBase
{
    //command that is binded to button
    private DelegateCommand getCommand;
    public ICommand GetCommand
    {
        get
        {
            if (getCommand == null)
                getCommand = new DelegateCommand(param => this.func(param), null);
            return getCommand;
        }
    }
    //method that will handle button click, and in it i'm sending a message
    //to MainWindowViewModel throug Mediator class 
    //and that is allso a problem place because in theory i should
    //pass the opposite UserControl object , but from here i have no 
    //acces to it
    private void func(object obj)
    {
        Mediator.Instance.NotifyColleagues(
            ViewModelMessages.UserWroteSomething,
            "PROBLEM PLACE");
    }
}

}

SecondUserControl

<UserControl x:Class="TESTPROJECT.SecondUserControl"
         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:TESTPROJECT"
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">
<Grid>
    <Button Command="{Binding GetCommand}">
        Hello, i'm second user control!
    </Button>
</Grid>

SecondUserControl ViewModel

namespace TESTPROJECT
{
class SecondUserControlViewModel : ViewModelBase
{
    //command that is binded to button
    private DelegateCommand getCommand;
    public ICommand GetCommand
    {
        get
        {
            if (getCommand == null)
                getCommand = new DelegateCommand(param => this.func(param), null);
            return getCommand;
        }
    }
    //method that will handle button click, and in it i'm sending a message
    //to MainWindowViewModel throug Mediator class 
    //and that is allso a problem place because in theory i should
    //pass the opposite UserControl object , but from here i have no 
    //acces to it
    private void func(object obj)
    {
        Mediator.Instance.NotifyColleagues(
            ViewModelMessages.UserWroteSomething,
            "PROBLEM PLACE");
    }
}

}

班级调解员和枚举ViewModelMessages

namespace TESTPROJECT
{
//this enum holding some kind of event names fro example UserWroteSomething
// is a name of switching one UserControl to another
public enum ViewModelMessages { UserWroteSomething = 1 };

class Mediator
{
    //Singletone part
    private static Mediator instance;
    public static Mediator Instance
    {
        get
        {
            if (instance == null)
                instance = new Mediator();
            return instance;
        }
    }
    private Mediator() { }
    //Singletone part

    //collection listeners that holds event names and handler functions
    List<KeyValuePair<ViewModelMessages, Action<Object>>> internalList = 
        new List<KeyValuePair<ViewModelMessages, Action<Object>>>();


    //new listener registration
    public void Register(Action<object> callBack, ViewModelMessages message)
    {
        internalList.Add(
            new KeyValuePair<ViewModelMessages, Action<Object>>(message, callBack));
    }

    // notifying all the listener about some changes
    // and those whose names fits will react
    public void NotifyColleagues(ViewModelMessages message, object args)
    {
        foreach(KeyValuePair<ViewModelMessages, Action<Object>> KwP in internalList)
            if(KwP.Key == message)
                KwP.Value(args);
    }
}

}

App起点

    public partial class App : Application
{
    private void Application_Startup(object sender, StartupEventArgs e)
    {
        FirstUserControl first = new FirstUserControl() { DataContext = new FirstUserControlViewModel() };
        SecondUserControl second = new SecondUserControl() { DataContext = new SecondUserControlViewModel() };

        new MainWindow()
        {
            DataContext = new MainWindowViewModel() { PagesControl = first }
        }.ShowDialog();
    }
}

Answer 1

如果我理解正确，您希望在当前活动视图模型上发生某个操作时（例如，您按一个按钮）导航到另一个视图（或分别是视图模型）。

如果你想使用你的中介，你可以像这样构建它：

public class Mediator
{
    // These fields should be set via Constructor Injection
    private readonly MainWindowViewModel mainWindowViewModel;
    private readonly Dictionary<ViewModelId, IViewFactory> viewFactories;        

    public void NotifyColleagues(ViewModelId targetViewModelId, ViewModelArguments arguments)
    {
        var targetFactory = this.viewModelFactories[targetViewModelId];
        var view = targetFactory.Create(viewModelArguments);
        this.mainWindowViewModel.PagesControl = view;
    }

    // other members omitted to keep the example small
}

然后，您将为每个视图创建一个工厂 - 视图模型组合。使用ViewModelArguments，您可以将信息传递到源自其他视图模型的新创建的视图模型中。 ViewModelId可以是一个简单的枚举，就像您的ViewModelMessage一样，您也可以使用视图模型的Type（我建议您继续使用）。

此外，我建议您不要在Mediator类上使用私有构造函数，因为否则您无法传入mainWindowViewModel和视图工厂的字典。您应该能够在Application-Startup方法中配置它。

此外，请注意，还有许多其他方法可以构建MVVM应用程序，例如：使用数据模板来实例化视图模型的视图 - 但我认为这对你的小例子来说有点过于紧张。

无法在MVVM

1 个答案: