Opening new window in MVVM WPF

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You say “creating window instance and showing window from view model is violation of MVVM”. This is correct.

You are now trying to create an interface that takes a type of view specified by the VM. This is just as much of a violation. You may have abstracted away the creation logic behind an interface, but you are still requesting view creations from within the VM.

VM’s should only care about creating VM’s. If you really need a new window to host the new VM, then provide an interface as you have done, but one that does NOT take a view. Why do you need the view? Most (VM first) MVVM projects use implicit datatemplates to associate a view with a particular VM. The VM knows nothing about them.

Like this:

class WindowService:IWindowService
{
    public void ShowWindow(object viewModel)
    {
        var win = new Window();
        win.Content = viewModel;
        win.Show();
    }
}

Obviously you need to make sure you have your VM->View implicit templates set up in app.xaml for this to work. This is just standard VM first MVVM.

eg:

<Application x:Class="My.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:vm="clr-namespace:My.App.ViewModels"
             xmlns:vw="clr-namespace:My.App.Views"
             StartupUri="MainWindow.xaml">
    <Application.Resources>

        <DataTemplate DataType="{x:Type vm:MyVM}">
            <vw:MyView/>
        </DataTemplate>

    </Application.Resources>
</Application>

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