App.xaml does not generate initialize method when only resource dictionary applied using MVVM locator

[marik91]

• .NET Core Version: 3.1
• Visual Studio version: VS 16.5.4
• Windows version: 18363.778
• Does the bug reproduce also in WPF for .NET Framework 4.8?: Not tested

Problem description:
when using MVVM pattern StartupUri property is deleted from app.xaml, instead in application.resource resource dictionary is added and static resource for view model locator is added. then resolving view and trying to call show on it will throw runtime exception "Cannot find resource named 'Locator'. Resource names are case sensitive.". Turns out when only single static resource is added InitializeComponent method is not generated. Work around inside resource dictionary add any mapping to merged resource dictionary then InitializeComponent method is generated and application works as expected

Expected behavior:
When added locator resource, InitializeComponent method should be generated

Minimal repro:
Was using Host class to enable core IoC and Mvvmlight
// App.xaml: not generating InitializeComponent

<Application x:Class="WpfApp1.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:WpfApp1"
             >
    <Application.Resources>
         <ResourceDictionary>
             <local:ViewModelLocator x:Key="Locator" />
         </ResourceDictionary>
    </Application.Resources>
</Application>

// App.xaml generating InitializeComponent

<Application x:Class="WpfApp1.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:WpfApp1"
             >
    <Application.Resources>
         <ResourceDictionary>
             <local:ViewModelLocator x:Key="Locator" />
             <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="styles.xaml" /> <!--empty resource dictionary -->
            </ResourceDictionary.MergedDictionaries>
         </ResourceDictionary>
    </Application.Resources>
</Application>

// MainWindow.xaml

<Window x:Class="WpfApp1.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"
        DataContext="{Binding Source={StaticResource Locator}, Path=MainViewModel}"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>

    </Grid>
</Window>

// ViewModelLocator

public class ViewModelLocator
{
    public MainViewModel MainViewModel => App.ServiceProvider.GetRequiredService<MainViewModel>();
}

[rladuca]

@dotnet/wpf-developers This reminds me of #2543. That reproduced in .NET 4.8 as well, it's likely a long-standing issue with PresentationBuildTasks generating code.

[ThomasGoulet73]

This bug should be fixed by #8853. For now, you can workaround this issue by adding a dummy item in <Application.Resources>.