Description

When using VisualStateManager.VisualStateGroups in XAML with the source generator, the app throws InvalidOperationException: VisualStateGroup Names must be unique at first startup.

Expected Behavior

The page should load without errors — each VisualStateGroup name appears only once in the XAML.

Actual Behavior

System.InvalidOperationException: VisualStateGroup Names must be unique
   at Microsoft.Maui.Controls.VisualStateManager.Validate(...)

Steps to Reproduce

1. Create a page with a Button that has VisualStateManager.VisualStateGroups:

<Button Text="Press me">
    <VisualStateManager.VisualStateGroups>
        <VisualStateGroup Name="CommonStates">
            <VisualState Name="Normal">
                <VisualState.Setters>
                    <Setter Property="BackgroundColor" Value="White" />
                </VisualState.Setters>
            </VisualState>
            <VisualState Name="Pressed">
                <VisualState.Setters>
                    <Setter Property="BackgroundColor" Value="LightGray" />
                </VisualState.Setters>
            </VisualState>
        </VisualStateGroup>
    </VisualStateManager.VisualStateGroups>
</Button>

2. Build and run — crashes at startup

Root Cause

The SG-generated InitializeComponent processes the VisualStateManager.VisualStateGroups collection-type attached property. During processing, the VisualStateGroupList validation callback fires and finds a duplicate "CommonStates" name — likely because the group is added to the collection during construction and then the list is assigned to the property, triggering re-validation against a pre-existing entry.

Affected Area

• XAML Source Generator (SourceGen)
• SetPropertiesVisitor handling of collection-type attached properties with named items