Static resources declared in App.xaml are not applied

[zbigniew-gajewski]

Steps to reproduce:

1. Clone this repository, restore nuget packages, rebuild.
2. Run UnoTest.Web project (right click, start new instance) - clicking the button will increase the counter - OK.
3. Change MainPage.xaml by adding DataContext attribute to the header:

<Page x:Class="UnoTest.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:local="using:UnoTest"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      mc:Ignorable="d"
      DataContext="{Binding MainPageViewModelInstance, Source={StaticResource Locator}}">
    
        <Grid  Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
...
</Page>

4. In MainPage.xaml.cs remove (or comment) line creating a new instance of the MainPageViewModel class:

public sealed partial class MainPage : Page
{
        public MainPage()
        {
            InitializeComponent();
//            DataContext = new MainPageViewModel();
        }
  } 

5. Rebuild the whole solution.

Result:
6. Run UnoTest.UWP project (right click, start new instance) - clicking the button will increase the counter - correct behavior after change.
7. Run UnoTest.Web project (right click, start new instance) - clicking the button will not increase the counter - bad behavior after change.

Expected result:
After running UnoTest.Web app, clicking the button should increase the counter.

[jeromelaban]

This is a known issue for WASM, this works for iOS and Android.

The best workaround for now is to declare it in a merged resource dictionary.

[carldebilly]

I reproduced the problem and I found the cause... it's very far from the reported bug.

The actual cause

The Wasm version of MvvmLight will use the netstandard1.0 version of the package and the IoC in this version won't implement the IServiceLocator.

See those lines: https://github.com/nventive/uno.mvvmlight/blob/3408287579ace291c9519edefc8017df6a151aac/GalaSoft.MvvmLight/GalaSoft.MvvmLight.Extras%20(PCL)/Ioc/ISimpleIoc.cs#L38-L40

Since the project Uno.Core is compiled in netstandard2.0, it will include his own version of CommonServiceLocator (v1.3) as defined in this bug I just opened: unoplatform/Uno.Core#53

What is happening in the app

1. The initial navigation to MainPage.xaml will be initiated

2. In the MainPage.xaml InitializeComponent(), Uno will successfully resolve the Locator resource

3. Uno will call the MainPageViewModelInstance property of ViewModelLocator

4. This one will cast SimpleIoc.Default as IServiceLocator, which is not implemented this way

   Code here: https://github.com/zbigniew-gajewski/uno-wasm-aspnet-core/blob/78e9491427166d4a4242ddbec85e7080c38f51e9/UnoTest/UnoTest.Shared/ViewModels/ViewModelLocator.cs#L24

5. A null-reference exception will terminate the initial navigation, leading to the false interpretation there's a problem with resources.

I will close this bug as not related to Uno directly (the real issue has been created in Uno.Core project). Feel free to reopen it or ask more details.

[carldebilly]

Ooohhh... by the way, to find this problem I found those 2 assemblies must be removed from linker in the LinkerConfig.xml:

<assembly fullname="UnoTest.Wasm" />
<assembly fullname="GalaSoft.MvvmLight.Platform" />

[zbigniew-gajewski]

1. Thanks for diagnosing the bug.
2. Unfortunately without <assembly fullname="UnoTest.Wasm" /> accessing data with BreezeSharp doesn't work, I mean, the list with received data is not displayed.

[carldebilly]

When I said removed from linker, it means those lines must be added to the config file ;-)

Sorry for the confusion.

[zbigniew-gajewski]

Aaa, OK :) Thanks.