[Bug] xamarin forms 4.8 Uwp shell excepion on navigation ArgumentException: An item with the same key has already been added. Key: background

[filipoff2]

After update to "Xamarin.Forms" Version="4.8.0.1269"

Getting other exception on
ArgumentException: An item with the same key has already been added. Key: background

line 71:
rootFrame.Navigate(typeof(MainPage), e.Arguments);
In
https://github.com/filipoff2/MagicGradients/blob/issues/Add-UWP-Playground-Project-45/Playground/Playground.UWP/App.xaml.cs

Result:
On 4.8 App is crashing on start
On 4.5 navigation was not done.

[filipoff2]

#8498 (comment)

[filipoff2]

https://github.com/filipoff2/MagicGradients/tree/issues/Add-UWP-Playground-Project-45

https://github.com/filipoff2/MagicGradients/tree/issues/Add-UWP-to-playground-project-with-Xamarin-Forms-4-8/Playground

[PureWeen]

@filipoff2 i don't think this is a shell bug

I ran your code and the exception is happening here

            styleList.Add(styleAttributeInstance);
            dictionaryAdd.Invoke(styleProperties, new object[] { name, styleList });
        }

in your StyleSheet.cs class

I'm not sure what's all going on in there but if you could break that out into a smaller repro. Maybe this is an issue on your side? I see reflection so maybe it's triggering an unsupported scenario?

For fun I changed "add" to "tryadd" and then it loads

[mgierlasinski]

@filipoff2 @PureWeen This is not an issue with Shell but with Magic Gradients and Brushes working together. In Forms 4.8 there was new background css property introduced, we use exact same property in Magic Gradients. We are working on fix, registering css properties outside Forms assembly is a reflection pain 😞 As @PureWeen pointed this is registration issue, if there is an existing background key, we should modify value instead of adding new entry.

See Bug report for details.

[filipoff2]

Ok well I did update something was working after update not so conclusion was fast.

Registering css properties outside Forms assembly should be more formalized in such case.

@PureWeen @mgierlasinski is there an new feature request for formalize Registering css properties outside Forms?

[filipoff2]

ok I'm closing issue.
This one is hobby for me.
For commercial projects: Less 3rd party nuggets are used in xamarin client solution than it is more chance it won't be hit by xamarin update, what happened to me few times.