XamlC error XFC0045 with maui dotnet 9 preview 3

[rogerbriggen]

Description

If you use compiled bindings and you use x:Reference Bindings they don't work with dotnet 9 preview 3. It works fine with dotnet 9 preview 2 and dotnet 8.

Steps to Reproduce

1. Clone the repo
2. Install dotnet 9 preview 3
3. dotnet workload restore
4. dotnet build -> you will get the error

Link to public reproduction project repository

https://github.com/rogerbriggen/mauidotnet9pre3_collectionview

Version with bug

9.0.0-preview.3.10457

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

9.0.0-preview.2.10293

Affected platforms

Android, Windows

Affected platform versions

No response

Did you find any workaround?

No

Relevant log output

C:\temp\mauidotnet9pre3_collectionview-master>dotnet build
Wiederherstellung abgeschlossen (2.0s)
Sie verwenden eine Vorschauversion von .NET. Weitere Informationen: https://aka.ms/dotnet-support-policy
  mauidotnet9pre3_collectionview net9.0-windows10.0.19041.0 failed with 1 error(s) (9.7s)
    MainPage.xaml(16,17): XamlC error XFC0045: Binding: Property "SelectedItem" not found on "mauidotnet9pre3_collectionview.MainPageViewModel".
  mauidotnet9pre3_collectionview net9.0-android failed with 1 error(s) (13.1s)
    MainPage.xaml(16,17): XamlC error XFC0045: Binding: Property "SelectedItem" not found on "mauidotnet9pre3_collectionview.MainPageViewModel".

Erstellen von failed with 2 error(s) in 15.4s

[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!

Closed similar issues:

• XamlC compiler null-refs when encountering a binding to an array access (#10396), similarity score: 0.71
• Resolving an x:Reference in a RELEASE build picks the wrong element in some cases. (#8149), similarity score: 0.71
• XamlC XC0022 error : Binding could be compiled if x:DataType is specified. (#20568), similarity score: 0.71
• [regression/8.0.0-preview.1.7762] [WinUI] CollectionView runtime binding errors when loading the ItemSource asynchronously (#16787), similarity score: 0.70
• The "XamlCTask" task failed unexpectedly. (#21910), similarity score: 0.70

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[rogerbriggen]

The same error if you use
SelectionChangedCommandParameter="{Binding Source={RelativeSource Self}, Path=SelectedItem}"

[kevinxufei]

Verified this issue with Visual Studio 17.10 Preview 7.0 + NET9.0 SDK (9.0.100-preview.3.24204.13).
MauiVersion = 9.0.0-preview.3.10457, repro this issue;
MauiVersion = 9.0.0-preview.2.10293, works well.

[cgp1976]

Hi guys, I am facing these issues as well. Is there any workaround settings where we can bypass the error from XamlC

similar to
<XFDisableTargetsValidation>True</XFDisableTargetsValidation>

cos right now, I can't build and compile the project. kindly advise.

[drasticactions]

maui/src/Controls/src/Build.Tasks/BuildException.cs

Line 67 in 39f90ee

public static BuildExceptionCode BindingPropertyNotFound = new BuildExceptionCode("XFC", 0045, nameof(BindingPropertyNotFound), "");

maui/loc/pl/src/Controls/src/Build.Tasks/ErrorMessages.resx.lcl

Lines 69 to 77 in 39f90ee

	<Item ItemId=";BindingPropertyNotFound" ItemType="0;.resx" PsrId="211" InstFlg="true" Leaf="true">
	<Str Cat="Text">
	<Val><![CDATA[Binding: Property "{0}" not found on "{1}".]]></Val>
	</Str>
	<Disp Icon="Str" />
	<Cmts>
	<Cmt Name="Dev"><![CDATA[0 is property name, 1 is type name]]></Cmt>
	</Cmts>
	</Item>

There's been a few changes in SetPropertiesVisitor since Preview2, and I think this is the only place that throws that exception: https://github.com/dotnet/maui/blame/main/src/Controls/src/Build.Tasks/SetPropertiesVisitor.cs

@simonrozsival Would you have any ideas what it could be?

[simonrozsival]

@rogerbriggen @drasticactions previously, any binding with Source wasn't compiled. After a recent change (#20610), we can now compile all bindings. Unfortunately, we can't infer the x:DataType form Source yet (#21834) and so in this case, the compiler doesn't know that it shouldn't be looking for the property SelectedItem on MainPageViewModel but instead on CollectionView.

As a fix, you can set the x:DataType on the binding that shouldn't inherit the parent's x:DataType:

<CollectionView 
    x:Name="myCollection" 
    ItemsSource="{Binding Items}" 
    ...
    SelectionChangedCommandParameter="{Binding Source={x:Reference myCollection}, Path=SelectedItem, x:DataType=CollectionView}">
    <CollectionView.ItemTemplate>
     ...
    </CollectionView.ItemTemplate>
</CollectionView>

Does this solve your problem?

[cgp1976]

one thing I found out is that when any parent element has assigned the x Attribute x:DataType with value, those child elements will be overriding with the parent value... basically, it is using the parent context to find the binding hence it throws the Property Binding not found.

[cgp1976]

@rogerbriggen @drasticactions previously, any binding with Source wasn't compiled. After a recent change (#20610), we can now compile all bindings. Unfortunately, we can't infer the x:DataType form Source yet (#21834) and so in this case, the compiler doesn't know that it shouldn't be looking for the property SelectedItem on MainPageViewModel but instead on CollectionView.

As a fix, you can set the x:DataType on the binding that shouldn't inherit the parent's x:DataType:

<CollectionView 
    x:Name="myCollection" 
    ItemsSource="{Binding Items}" 
    ...
    SelectionChangedCommandParameter="{Binding Source={x:Reference myCollection}, Path=SelectedItem, x:DataType=CollectionView}">
    <CollectionView.ItemTemplate>
     ...
    </CollectionView.ItemTemplate>
</CollectionView>

Does this solve your problem?
Many thanks for the response. Seem like I just need to remove the x:DataType for the time being.

[drasticactions]

@simonrozsival Okay, that makes sense. Should this issue be closed then and duplicated under #21834?

[simonrozsival]

@drasticactions I'm not sure. I think this is mostly a documentation issue. We've made changes to how XamlC compiles bindings in .NET 9, but we haven't updated the docs yet. I think we need a new issue that will track the necessary changes to documentation and then we can close this issue.

[rogerbriggen]

@rogerbriggen @drasticactions previously, any binding with Source wasn't compiled. After a recent change (#20610), we can now compile all bindings. Unfortunately, we can't infer the x:DataType form Source yet (#21834) and so in this case, the compiler doesn't know that it shouldn't be looking for the property SelectedItem on MainPageViewModel but instead on CollectionView.

As a fix, you can set the x:DataType on the binding that shouldn't inherit the parent's x:DataType:

<CollectionView 
    x:Name="myCollection" 
    ItemsSource="{Binding Items}" 
    ...
    SelectionChangedCommandParameter="{Binding Source={x:Reference myCollection}, Path=SelectedItem, x:DataType=CollectionView}">
    <CollectionView.ItemTemplate>
     ...
    </CollectionView.ItemTemplate>
</CollectionView>

Does this solve your problem?

@cgp1976 Yes, this solves this issue. The only thing which is, that Visual Studio shows an error

The text means "the datatype property was not found in type BindingExtension.
Do I need to create a bug for that? Where?

[simonrozsival]

@rogerbriggen I think this is the same warning we saw in #21434. This seems to be a bug in the XAML editor in VS. I wonder where the best place to report it is (cc @StephaneDelcroix @PureWeen).

[drasticactions]

@mgoertz-msft Would you know?

[mgoertz-msft]

Xamarin and MAUI never cease to surprise me on what they allow that other platforms like WPF and UWP/WinUI don't. I had no idea this was allowed to be used that way.

[simonrozsival]

I reported the issue in the VS Code extension here: microsoft/vscode-dotnettools#1131

[daltzctr]

This issue is unfortunate and blocks my migration to .NET 9. For context, I don't see an obvious way to do

Command="{Binding Source={Reference root}, Path=BindingContext.MyCommand}"

where root refers to a top level ContentView. The idea is being able to use commands on a top level ViewModel inside of a CollectionView.ItemTemplate. I have no idea what to put for DataType here

[mgoertz-msft]

FYI, the XLS error in the editor has been fixed (see VS Code Issue #1131).

@StephaneDelcroix would know most about the XFC error.

[simonrozsival]

@daltzctr the x:DataType should be set to the type of the source which is either the BindingContext (often inherited from the parent), or the type of the Source that you pass explicitly to the binding. In your case, you should use the type of root:

Command="{Binding Source={Reference root}, Path=BindingContext.MyCommand, x:DataType=ContentView}"

If this doesn't solve your problem, please share more of your XAML so we can see more context of the component tree.

[simonrozsival]

@rogerbriggen I'm closing this issue now since the new behavior has been explained in the thread and we'll cover it in the docs in time for the release of .NET 9 (this is tracked here: dotnet/docs-maui#2187). Please feel free to reopen this issue if something is still unclear.

[daltzctr]

@simonrozsival that doesn't work and throws an exception
when using

Command="{Binding Source={Reference root}, Path=BindingContext.MyCommand, x:DataType=ContentView}"

throws

XamlC error XC0045: Binding: Property "MyCommand" not found on "System.Object".