How to use method extension in Maui xaml?

Question

I have a Dto object:

public class SearchResultDto
{
  public bool IsOne { get; set; };

  public bool IsTwo { get; set; }
}

And I have a method extension:

public static class SearchResultDtoExtension{
  public static bool IsBoth(this SearchResultDto dto)
  {
    return dto.IsOne && dto.IsTwo;
  }
}

At my ViewModel I can successful use searchResultDto.IsBoth();

I want this extension use in xaml like:

IsVisible={Binding IsBoth()}

It does not work.

How can I use a method extension in xaml?

my code:

<listView:SfListView.ItemTemplate>
    <DataTemplate x:DataType="contracts:SearchResultDto">
            <VerticalStackLayout IsVisible="{Binding **IsBoth()**}"

Answer 1

As explained in comments you can't bind methods in XAML, you could instead use one of the two approaches:

1. Using a ValueConverter:

public class IsBothConverter : IValueConverter
{
    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
        => (value as SearchResultDto)?.IsBoth();


    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

    <ContentPage.Resources>
        <ResourceDictionary>
            <local:IsBothConverter x:Key="isBothConverter" />
        </ResourceDictionary>
    </ContentPage.Resources>
...

 <VerticalStackLayout IsVisible="{Binding ., Converter={StaticResource isBothConverter}}" />

2. Using an auto property (like @julian suggested in comments) Both inside your ViewModel: Note that whenever the property of type SearchResultDto changed we raise a property changed event for Both property also.

SearchResultDto dto = new() { IsOne = true, IsTwo = true };

public SearchResultDto Dto
{
    get => dto;
    set
    {
        dto = value;
        OnPropertyChanged(nameof(Dto));
        OnPropertyChanged(nameof(Both));
    }
}

public bool Both => (dto is null) ? false : dto.IsOne && dto.IsTwo;

I see that you are inside a datatemplate, thus you have to ensure a correct Source and x:DataType when binding to Both:

 <VerticalStackLayout IsVisible="{Binding Path="Both", Source="..."}" />

3. Using a third auto property inside your model (this goes against mvvm pattern as the model and the view are not properly decoupled)

public class SearchResultDto
{
    public bool IsOne { get; set; }
    public bool IsTwo { get; set; }
    public bool IsBoth => IsOne && IsTwo;
}

 <VerticalStackLayout IsVisible="{Binding IsBoth}" />