iOS Numeric Format setting not respected

[LiamMorrow]

Description

When using decimal.Parse using the default CultureInfo (or not specifying one), MAUI does not respect the user's decimal separator options in iOS. Instead, it simply uses the language's default. What this means is that when a user is prompted for numerical, decimal input, the iOS keyboard presents them with a comma separator (as they have configured), but decimal.Parse treats it as a grouping separator.

Note that if the user specifies a LANGUAGE which uses commas as a decimal separator, everything works as expected and decimal parse treats commas as decimal separators.

Screenshot showing how the default culture parses a decimal, and the correct parsing

Screenshot showing that the keyboard only allows entering decimals with commas

Code driving the parsing logic

 if (decimal.TryParse(e.NewTextValue, out decimal result))
        {
            resultLabel.Text = $"Parsed value with default culture: {result}";
        }
        else
        {
            resultLabel.Text = "Invalid input";
        }
#if IOS
        var correctedCulture = CultureInfo.CurrentCulture.Clone() as CultureInfo;
        correctedCulture.NumberFormat.NumberDecimalSeparator = NSLocale
            .CurrentLocale
            .DecimalSeparator;
        correctedCulture.NumberFormat.NumberGroupSeparator = NSLocale
            .CurrentLocale
            .GroupingSeparator;

        if (decimal.TryParse(e.NewTextValue, correctedCulture, out decimal result2))
        {
            resultLabel2.Text = $"Parsed value with culture from IOS settings: {result2}";
        }
        else
        {
            resultLabel2.Text = "Invalid input";
        }
#endif

Video showing off behaviour

Screen.Recording.2024-12-04.at.12.14.58.mov

Steps to Reproduce

1. Open iOS settings -> General -> Language
2. Set language to English
3. Set Number Format to 1.234.234,83 (the one which uses comma as a decimal separator)
4. In a Maui app type in a numeric editor (notice iOS presents only a comma as the decimal separator)
5. Notice that decimal.Parse treats the comma as a grouping separator

An example repo for parsing can be found here:
https://github.com/LiamMorrow/maui-decimal-repro

Link to public reproduction project repository

https://github.com/LiamMorrow/maui-decimal-repro

Version with bug

9.0.12 SR1.2

Is this a regression from previous behavior?

No, this is something new

Last version that worked well

Unknown/Other

Affected platforms

iOS

Affected platform versions

iOS 18

Did you find any workaround?

Cloning the current culture, then using the proper separators in the clone, and setting it as the current culture on app startup does fix this. See this PR for an example.

Relevant log output

[rolfbjarne]

This sounds like the default CultureInfo isn't instantiated correctly, which is an issue for dotnet/runtime.

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Tagging subscribers to this area: @dotnet/area-system-numerics
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[dotnet-policy-service]

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[dotnet-policy-service]

Tagging subscribers to 'os-ios': @vitek-karas, @kotlarmilos, @ivanpovazan, @steveisok, @akoeplinger
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[tarekgh]

@matouskozak could you please have a look and triage?

[LiamMorrow]

For the record, this was originally reported here:
LiamMorrow/LiftLog#332

Note that the user seems to think it is due to the mix of Swedish&English keyboard, introduced in ios18

[matouskozak]

@LiamMorrow Thanks a lot for the great issue description with concrete examples. I'm able to reproduce the issue, on both .net 8 and .net 9 MAUI apps.

Do you with which version of .NET it used used to work correctly?

Anyways, I'll investigate why the CurrentCulture is not set properly with the iOS number format setting.

[LiamMorrow]

Thanks @matouskozak for looking into it!

Do you know when was the last time this used to work correctly?

I have a feeling it has never worked correctly, however iOS 18 has released new keyboards which allow for multi locale keyboards which has probably made it much easier for it to happen. I don't think many users would stray from their default locale's number format otherwise. The user who reported it to me says it started occuring when they switched to the Swedish/English keyboard.