如何与2个或更多ViewModel进行交互

Question

I have written a tool in which a ListBox is bound to a ObserservableCollection<object> with varying datatypes I've define. I use a PropertyDataTemplateSelector to present the data in the ListBox. The PropertyDataTemplateSelector references several DataTemplates that are set as UserControls . There is a background class that provides logic to the PropertyDataTemplateSelector by checking the object type and then applying the correct DataTemplate .

Here's an abbreviated example of the XAML for the UserControls and the MainWindow .

UserControl1

    <TextBlock Text="{Binding Path=Val1}"
               Style="{StaticResourse Yes}" />

    <Button Content="I'm Button 1"
            Command="{Binding Path=PathtoCommand1}"
            CommandParameter="{Binding Parameter1}"
            IsEnabled="{Binding IsEnabled1}" />

    <Button Content="I'm Button 2"
            Command="{Binding Path=PathtoCommand2}"
            CommandParameter="{Binding Parameter2}"
            IsEnabled="{Binding IsEnabled2}"
            Tag="{Binding Path="DataContext.TagItem2}">

       <Button.ContextMenu>
         <ContextMenu>
           <MenuItem IsCheckable="True"
                     IsChecked="{Binding Path=Tag}"
                     DataContext="{Binding Path=PlacementTarget, RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}}" />
         </ContextMenu>
       </Button.ContextMenu>

    </Button>
  </StackPanel>
</UserControl>

UserControlN

<UserControl x:Class="AwesomerControl">
  <StackPanel Orientation="Vertical">

    <TextBlock Text="{Binding Path=FancyName2}"
               Style="{StaticResourse Yes}" />

    <Button Content="Clicker 1"
            Command="{Binding Path=DoSomethingGreat1}"
            CommandParameter="{Binding Greatness1}"
            IsEnabled="{Binding IsTurnedOn1}" />

    <Button Content="Clicker 2"
            Command="{Binding Path=DoSomethingGreat2}"
            CommandParameter="{Binding Greaterness2}"
            IsEnabled="{Binding IsTurnedOn2}"
            Tag="{Binding Path="DataContext.TagItem2}">

       <Button.ContextMenu>
         <ContextMenu>
           <MenuItem IsCheckable="True"
                     IsChecked="{Binding Path=Tag}"
                     DataContext="{Binding Path=PlacementTarget, RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}}" />
         </ContextMenu>
       </Button.ContextMenu>

    </Button>
  </StackPanel>
</UserControl>

Here I set the UserControls to a specified DataTemplate . The UserControls were moved out to make the XAML easier to read/navigate. In actuality the UserControls are a few hundred lines each.

<Window.Resources>
  <DataTemplate x:Key"Template1">
     <customControls:AwesomeControl/>
  </DataTemplate>
  ...
  <DataTemplate x:Key"TemplateN">
     <customControls:AwesomerControl/>
  </DataTemplate>


  <dts:PropertyDataTemplateSelector x:Key="templateselector"
                                    Template1="{StaticResource Template1"}
                                    ...
                                    TemplateN="{StaticResource TemplateN"}
</Window.Resources>

The ListBox is defined as this.

<ListBox ItemSource="{Binding Path=CollectionofMyObjects}"
         ItemTemplateSelector="{StaticResource templateselector}" />

I am using a single ViewModel to drive the MainWindow and the UserControls .

So that's where I'm at, essentially. I have this currently working as I'd like, but in an ongoing effort to learn (this is my first MVVM/WPF/C# project) I'd like to keep exploring how to make my code "better" (however that's defined). I'm not looking to solve an error here. So to avoid a general/broad question, I'll ask what I think I want to know. Someone can correct me and I'll update the "question(s)" appropriately

Question: How can I go about producing a ViewModel for each of the UserControls ? Some of the ViewModels , for the UserControls , will occasionally require two-way communication to the MainWindow_ViewModel . The main crux of my problem is figuring out how the multiple VMs will communicate.

Answer 1

You're close, but it's not quite MVVM yet. ;)

1. First, break out all the functionality that is relevant to each UserControl into their own classes. These are your view-model classes.
2. Your controls should now become "view" classes, and they deserve their own mark-up file. Rather than use a template selector, you can use the DataTemplate.DataType to automatically connect the view-model class type to its view.

There are a lot of options for communication between view-models. To further your education, I'd consider looking at a light-weight MVVM framework that has built-in solutions for communication. My personal favorite is Caliburn.Micro , which includes an EventAggregator , a service that provides the ability to publish an object from one view-model to another in a loosely-coupled fashion.

Keep learning, you're on the right track!