XamlC error : Value cannot be null. (Parameter 'key')

[mattleibow]

Description

Using this code:

https://github.com/mattleibow/scorecard-day-nft-marketplace/tree/issues/xamlc-null-key

And this command:

 *  Executing task: dotnet build -t:Run -p:Configuration=Debug -f net9.0-android -p:AdbTarget=-s%20emulator-5554 -p:AndroidAttachDebugger=true -p:AndroidSdbTargetPort=62984 -p:AndroidSdbHostPort=62984 -p:CustomAfterMicrosoftCSharpTargets="c:\Users\maleib\.vscode\extensions\ms-dotnettools.dotnet-maui-1.3.3-win32-x64\dist\resources\Custom.After.Microsoft.CSharp.targets" -p:MauiVSCodeBuildOutputFile="C:\Users\maleib\AppData\Local\Temp\dotnet-maui\maui-vsc-02d574b0-4193-4d89-99d1-f44c0a215bea.json" -p:AndroidSdkDirectory="C:\Users\maleib\android-sdk" '-p:JavaSdkDirectory="C:\Program Files (x86)\Android\openjdk\jdk-17.0.8.101-hotspot"' -p:XamlTools="c:\Users\maleib\.vscode\extensions\ms-dotnettools.csharp-2.44.19-win32-x64\.xamlTools" D:\GitHub\scorecard-day-nft-marketplace\NFTMarketplaceApp\NFTMarketplaceApp.csproj 

You are using a preview version of .NET. See: https://aka.ms/dotnet-support-policy
  NFTMarketplaceApp net9.0-android failed with 1 error(s) and 4 warning(s) (2,7s)
    D:\GitHub\scorecard-day-nft-marketplace\NFTMarketplaceApp\ExplorePage.xaml.cs(13,16): warning CS8618: Non-nullable property 'Name' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.
    D:\GitHub\scorecard-day-nft-marketplace\NFTMarketplaceApp\ExplorePage.xaml.cs(14,16): warning CS8618: Non-nullable property 'Type' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.
    D:\GitHub\scorecard-day-nft-marketplace\NFTMarketplaceApp\ExplorePage.xaml.cs(16,16): warning CS8618: Non-nullable property 'Currency' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.
    D:\GitHub\scorecard-day-nft-marketplace\NFTMarketplaceApp\ExplorePage.xaml.cs(17,16): warning CS8618: Non-nullable property 'CurrencyName' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.
    D:\GitHub\scorecard-day-nft-marketplace\NFTMarketplaceApp\ExplorePage.xaml : XamlC error : Value cannot be null. (Parameter 'key')

Build failed with 1 error(s) and 4 warning(s) in 3,1s

I get this error:

D:\GitHub\scorecard-day-nft-marketplace\NFTMarketplaceApp\ExplorePage.xaml : XamlC error : Value cannot be null. (Parameter 'key')

Steps to Reproduce

Run the command or just open in VSCode and run.

Link to public reproduction project repository

https://github.com/mattleibow/scorecard-day-nft-marketplace/tree/issues/xamlc-null-key

Version with bug

9.0.0-preview.7.24407.4

Is this a regression from previous behavior?

Not sure, did not test other versions

Last version that worked well

Unknown/Other

Affected platforms

I was not able test on other platforms

Affected platform versions

No response

Did you find any workaround?

No response

Relevant log output

No response

[github-actions]

Hi I'm an AI powered bot that finds similar issues based off the issue title.

Please view the issues below to see if they solve your problem, and if the issue describes your problem please consider closing this one and thumbs upping the other issue to help us prioritize it. Thank you!

Open similar issues:

• XamlC error : The given key 'Microsoft.Maui.Controls.Xaml.ElementNode' was not present in the dictionary. (#23970), similarity score: 0.72
• XAML Compile Causes Failure at Run Time (#22110), similarity score: 0.70

Closed similar issues:

• [regression/8.0.0-rc.1.9171] Build error in .NET 8 RC1 - "XamlC error XFC0126: Resources in ResourceDictionary require a x:Key attribute" for resources that have a key (#17461), similarity score: 0.73
• The "Value cannot be null" errors are shown on an attempt to build a project with MauiVersion set to a previous value (#4812), similarity score: 0.70

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[mattleibow]

Seems to maybe be this chunk of code:

<CollectionView.ItemsSource>
    <x:Array Type="local:TopCollectionItem">
        <local:TopCollectionItem
            Name="Bear Baron"
            Type="Art Collection" />
        <local:TopCollectionItem />
        <local:TopCollectionItem />
        <local:TopCollectionItem />
        <local:TopCollectionItem />
        <local:TopCollectionItem />
    </x:Array>
</CollectionView.ItemsSource>