Regression from MAUI 8: Picker entries blank in release mode (Android)

[BioTurboNick]

Description

I have a Picker that is populated by an array of values. They are mapped to a localized string through a ValueConverter.

Since updating to MAUI 9, the picker is now full of blank entries in release mode.

Steps to Reproduce

XAML:

<ContentView.Resources>
    <ResourceDictionary>
        <vc:IntToPowerConverter x:Key="intToPower" />
    </ResourceDictionary>
</ContentView.Resources>

<Picker Grid.Column="2"
        FontSize="16"
        VerticalTextAlignment="End"
        ItemDisplayBinding="{Binding Converter={StaticResource intToPower}}">
    <Picker.ItemsSource>
        <x:Array Type="{x:Type x:Int32}">
            <x:Int32>0</x:Int32>
            <x:Int32>1</x:Int32>
            <x:Int32>2</x:Int32>
            <x:Int32>3</x:Int32>
            <x:Int32>4</x:Int32>
            <x:Int32>5</x:Int32>
            <x:Int32>6</x:Int32>
            <x:Int32>7</x:Int32>
            <x:Int32>8</x:Int32>
            <x:Int32>9</x:Int32>
        </x:Array>
    </Picker.ItemsSource>
</Picker>

C#:

static readonly char[] superscriptCharacters = ['⁰', '¹', '²', '³', '⁴', '⁵', '⁶', '⁷', '⁸', '⁹', '⁻'];
static readonly char[] characters = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-'];
static readonly Dictionary<char, char> superscriptDictionary = new(superscriptCharacters.Length);
const char times = '×';

public static string GetSuperscript(int exponentValue, CultureInfo culture)
{
    string formatedValue = exponentValue.ToString("D", culture);

    string formattedSuperscripts = string.Empty;

    for (int i = 0; i < formatedValue.Length; i++)
        formattedSuperscripts += superscriptDictionary[formatedValue[i]];

    return formattedSuperscripts;
}

public static string ToPowerOfTen(int value, CultureInfo culture)
{
    string formattedValue = string.Empty;

    if (value == 0) return formattedValue;

    formattedValue += times + 10.ToString(culture);

    if (value == 1) return formattedValue;

    formattedValue += GetSuperscript(value, culture);

    return formattedValue;
}

public class IntToPowerConverter :
    IValueConverter
{
    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
    {
        if (targetType != typeof(string))
            return new object();

        return value switch
        {
            int intValue => FormatHelpers.ToPowerOfTen(intValue, culture),
            _            => string.Empty
        };
    }

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

Link to public reproduction project repository

No response

Version with bug

9.0.10 SR1

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

8.0.92 SR9.2

Affected platforms

Android

Affected platform versions

Android 14

Did you find any workaround?

No response

Relevant log output

[mattleibow]

@simonrozsival This is using ItemDisplayBinding and I know we touched that in .NET 9...

[BioTurboNick]

FWIW I have confirmed that if I remove ItemDisplayBinding= the items show up.

[simonrozsival]

@BioTurboNick I cannot reproduce the problem in .NET 9 in the example you provided with this change to how superscriptDictionary is initialized (I assume you're setting this up elsewhere in your original codebase):

-static readonly Dictionary<char, char> superscriptDictionary = new(superscriptCharacters.Length);
+static readonly Dictionary<char, char> superscriptDictionary = characters.Zip(superscriptCharacters).ToDictionary(x => x.First, x => x.Second);

Even without this change, the picker displays two values ("" and "x10") which is different from the behavior you described.

Could you please share a full sample app which demonstrates the bug? There might be something else that causes the issue outside of the code you shared.

[dotnet-policy-service]

Hi @BioTurboNick. We have added the "s/needs-repro" label to this issue, which indicates that we require steps and sample code to reproduce the issue before we can take further action. Please try to create a minimal sample project/solution or code samples which reproduce the issue, ideally as a GitHub repo that we can clone. See more details about creating repros here: https://github.com/dotnet/maui/blob/main/.github/repro.md

This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.