多个视图绑定到多个ViewModels

Question

I want to create multiple instances of a SearchTagView and bind each of those to its own SearchTagViewModel .

I'm using the WAF framework for WPF which follows the MVVM-concept and furthermore Dependency injection (IoC). The application is developed for the SUR40 using the SurfaceSDK.

This means that the views are instantiated like this:

TagVisualizationDefinition tagDefinition = new TagVisualizationDefinition();
tagDefinition.Source = new Uri("Views/SearchTagView.xaml", UriKind.Relative);
tagVisualizer.Definitions.Add(tagDefinition);

tagVisualizer is a control element of type TagVisualizer in SearchView . So multiple SearchTagViews are placed in one SearchView . This works.

The problem is that because of dependency injection all SearchTagViews use the same SearchTagViewModel :

xmlns:vm="clr-namespace:Applications.ViewModels;assembly=Applications"

How can I use a different ViewModel for each View following the MVVM?

Answer 1

Every IoC framework that I've seen allows you to register types in two ways:

1. As a single instance (the same instance of the class is returned each time)
2. As a new instance each time it is resolved / injected

You'll need to figure out how to do #2 within your IoC framework.

The other MVVM-centric option is to declare a DataTemplate in your UI and add the ViewModels directly to the UI and have WPF automatically create the Views for it.

edit:

It looks like WAF is using MEF for IoC. You'll need to supply the [Export] attribute and specify it as non-shared.

Here's how to set a PartCreationPolicy with MEF from a previous question

Answer 2

You can use a view model locator for this purpose. Check out this .

Configure the view model locator to return a new instance of view model every time.

An example is given below, using mvvm light(even though you need not use mvvm light to use view model locator).

 public class ViewModelLocator
{
  public ViewModel1 VM1
        {
            get
            {
                return new ViewModel1();
            }
        }
}

In app.xaml, define a key for view model locator.If you nuget mvvmlight, this will happen automatically

<Application.Resources>
    <vm:ViewModelLocator x:Key="Locator" d:IsDataSource="True" xmlns:vm="clr-namespace:WpfApplicationmvvmlight.ViewModel" />
  </Application.Resources>

In the view, use the locator

<UserControl x:Class="WpfApplicationmvvmlight.View2"
             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" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300"
              DataContext="{Binding Source={StaticResource Locator}, Path=VM1}">
</UserControl>

Answer 3

Alan's hint concerning the non-shared attribute was good, but I couldn't use it to solve my problem. The problem was that the MEF is working before I init my TagVisualizationDefinitions .

The only solution was to set the binding in code-behind of the parent user control in the method for the event TagVisualization_Loaded