[Bug] Entry shows incorrect value when binding against a float property with StringFormat

[crenan]

Description

Xamarin Entry views are not working properly when using StringFormat in the binding configuration (e.g. 'F4') for a writable float property combined with an Android using a language other than US English (e.g. Portuguese Brazil).

Steps to Reproduce

1. Create a new AVD
   -> I used Nexus S
   -> API anything >= 25
   -> +Google APIs (does not matter but I use it anyways)

2. Start the AVD and configure the language for Português Brasil as main language
   -> Settings -> System -> Languages & Input -> Languages -> Add Language
   -> Choose Português, then Brasil as "suggested"
   -> Move the new language to top

3. Create a new Xamarin Forms project
   -> Blank
   -> Android (I don't have a Mac to test with iOS)

4. Update the solution's NuGet packages for the latest versions
   -> NetStandard.Library v2.0.3
   -> Xamarin.Essentials v1.5.1
   -> Xamarin.Forms v4.5.0.495

5. Create a new ViewModel class in the Class Library project that implements INotifyPropertyChanged

public class MainPageViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
}

6. Add a public property of type float using a private member

private float _vmFloatProperty = 0.567F;
public float VMFloatProperty
{
    get => _vmFloatProperty;
    set
    {
        _vmFloatProperty = value;
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(VMFloatProperty)));
    }
}

7. Modify the MainPage.xaml.
   -> Include the ContextBinding configuration to use the created ViewModel class

<ContentPage.BindingContext>
    <viewModel:MainPageViewModel/>
</ContentPage.BindingContext>

-> Include an Entry and bind the Text property to the float property of the ViewModel class with a StringFormat

<Entry Text="{Binding VMFloatProperty, StringFormat='{0:F4}'}" IsEnabled="False"/>

8. Start the app.

Expected Behavior

The Entry view should display the value in the correct format specified in the Binding configuration regardless of the OS culture.

Actual Behavior

The Entry view is trying to format the value using the OS culture defined. This is causing a wrong parsing with the value.
Also, if the property is displayed more than one time, the value starts to increase.

Basic Information

• Version with issue: v4.5.0.495
• Last known good version: Don't know
• IDE: Visual Studio 2019 v16.5.0
• Platform Target Frameworks:
  • iOS: None
  • Android: 7.1, 8.0, 8.1, 9.0
  • UWP: None
• Android SDK Tools v26.1.1
• Android SDK Platform-Tools v29.0.5
• Android SDK Build Tools v29.0.2 (also v28.0.3 installed)
• Android Emulator v29.3.0
• Nuget Packages: Only those installed with the template project (VS 2019 Xamarin Forms)
• Affected Devices: Tested with AVDs using API >= 25

Screenshots

Android Previewer is also affected.

Reproduction Link

EntryFloatBug.zip

Workaround

-> Use read-only properties.
-> Use Mode=OneWay in binding configuration.
-> Using a property of a class that does not implement INotifyPropertyChanged is the same as accessing a read-only property.

[StephaneDelcroix]

binding are supposed to use the CurrentUICulture for conversion, can you check what yours is set to ?

[crenan]

binding are supposed to use the CurrentUICulture for conversion, can you check what yours is set to ?

Hi, @StephaneDelcroix. Mine is set to "Português Brasil" (pt-br), as stated in the "Steps to Reproduce" above.

[kingces95]

I'm able to run the reproduction but my screenshot doesn't match yours. Could you be more specific about the expected and actual values? Could you either generate screenshots of actual and expected values and/or quote the values you expect and see?

[crenan]

Hey @kingces95!
Using the test project, the expected value is "0,5670" for ALL Entry views.
The actual values are different depending the way the Entry binding was configured and which kind of property it was bound.
If you take a look at the screenshot I sent, the correct value was displayed only in the 2nd, 3rd and last Entry view.

I'm able to run the reproduction but my screenshot doesn't match yours.

You need to set the language in the AVD to pt-br (Portuguese Brazil) or in your development O.S to see in Android Previewer.

[kingces95]

Reproduces as described.