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POHow to Interact with 2 or More ViewModels
 

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    <p>I have written a tool in which a ListBox is bound to a <code>ObserservableCollection&lt;object&gt;</code> with varying datatypes I've define. I use a <code>PropertyDataTemplateSelector</code> to present the data in the ListBox. The <code>PropertyDataTemplateSelector</code> references several <code>DataTemplates</code> that are set as <code>UserControls</code>. There is a background class that provides logic to the <code>PropertyDataTemplateSelector</code> by checking the <code>object</code> type and then applying the correct <code>DataTemplate</code>.</p> <p>Here's an abbreviated example of the XAML for the <code>UserControls</code> and the <code>MainWindow</code>.</p> <p>UserControl1 </p> <pre><code> &lt;TextBlock Text="{Binding Path=Val1}" Style="{StaticResourse Yes}" /&gt; &lt;Button Content="I'm Button 1" Command="{Binding Path=PathtoCommand1}" CommandParameter="{Binding Parameter1}" IsEnabled="{Binding IsEnabled1}" /&gt; &lt;Button Content="I'm Button 2" Command="{Binding Path=PathtoCommand2}" CommandParameter="{Binding Parameter2}" IsEnabled="{Binding IsEnabled2}" Tag="{Binding Path="DataContext.TagItem2}"&gt; &lt;Button.ContextMenu&gt; &lt;ContextMenu&gt; &lt;MenuItem IsCheckable="True" IsChecked="{Binding Path=Tag}" DataContext="{Binding Path=PlacementTarget, RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}}" /&gt; &lt;/ContextMenu&gt; &lt;/Button.ContextMenu&gt; &lt;/Button&gt; &lt;/StackPanel&gt; &lt;/UserControl&gt; </code></pre> <p>UserControlN</p> <pre><code>&lt;UserControl x:Class="AwesomerControl"&gt; &lt;StackPanel Orientation="Vertical"&gt; &lt;TextBlock Text="{Binding Path=FancyName2}" Style="{StaticResourse Yes}" /&gt; &lt;Button Content="Clicker 1" Command="{Binding Path=DoSomethingGreat1}" CommandParameter="{Binding Greatness1}" IsEnabled="{Binding IsTurnedOn1}" /&gt; &lt;Button Content="Clicker 2" Command="{Binding Path=DoSomethingGreat2}" CommandParameter="{Binding Greaterness2}" IsEnabled="{Binding IsTurnedOn2}" Tag="{Binding Path="DataContext.TagItem2}"&gt; &lt;Button.ContextMenu&gt; &lt;ContextMenu&gt; &lt;MenuItem IsCheckable="True" IsChecked="{Binding Path=Tag}" DataContext="{Binding Path=PlacementTarget, RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}}" /&gt; &lt;/ContextMenu&gt; &lt;/Button.ContextMenu&gt; &lt;/Button&gt; &lt;/StackPanel&gt; &lt;/UserControl&gt; </code></pre> <p>Here I set the <code>UserControls</code> to a specified <code>DataTemplate</code>. The UserControls were moved out to make the XAML easier to read/navigate. In actuality the UserControls are a few hundred lines each.</p> <pre><code>&lt;Window.Resources&gt; &lt;DataTemplate x:Key"Template1"&gt; &lt;customControls:AwesomeControl/&gt; &lt;/DataTemplate&gt; ... &lt;DataTemplate x:Key"TemplateN"&gt; &lt;customControls:AwesomerControl/&gt; &lt;/DataTemplate&gt; &lt;dts:PropertyDataTemplateSelector x:Key="templateselector" Template1="{StaticResource Template1"} ... TemplateN="{StaticResource TemplateN"} &lt;/Window.Resources&gt; </code></pre> <p>The <code>ListBox</code> is defined as this.</p> <pre><code>&lt;ListBox ItemSource="{Binding Path=CollectionofMyObjects}" ItemTemplateSelector="{StaticResource templateselector}" /&gt; </code></pre> <p>I am using a single <code>ViewModel</code> to drive the <code>MainWindow</code> and the <code>UserControls</code>.</p> <p>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</p> <p><strong>Question:</strong> How can I go about producing a <code>ViewModel</code> for each of the <code>UserControls</code>? Some of the <code>ViewModels</code>, for the <code>UserControls</code>, will occasionally require two-way communication to the <code>MainWindow_ViewModel</code>. The main crux of my problem is figuring out how the multiple VMs will communicate.</p>
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