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[Proposal] IsStringNullOrWhiteSpace Converter

See original GitHub issue

IsStringNullOrWhiteSpace Converters

Proposed
Prototype
Implementation
- iOS Support
- Android Support
- macOS Support
- Windows Support
Unit Tests
Sample
Documentation

Summary

The IsStringNullOrWhiteSpaceConverter is a converter that allows users to convert an incoming string binding to a bool value. This value represents if the incoming binding value is null or empty using string.IsNullOrWhiteSpace.

The IsStringNotNullOrWhiteSpaceConverter is a converter that allows users to convert an incoming string binding to a bool value. This value represents if the incoming binding value is null or empty using string.IsNullOrWhiteSpace .

Detailed Design

IsStringNullOrWhiteSpaceConverter.shared.cs

public class IsStringNullOrWhiteSpaceConverter : ValueConverterExtension, ICommunityToolkitValueConverter
{
  public object Convert(object? value, Type? targetType, object? parameter, CultureInfo? culture) => value is string stringValue ? string.IsNullOrWhiteSpace(stringValue) : throw new InvalidArgumentException("Binding must be of type string");

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

IsStringNotNullOrWhiteSpaceConverter.shared.cs

public class IsStringNotNullOrWhiteSpaceConverter : ValueConverterExtension, ICommunityToolkitValueConverter
{
  public object Convert(object? value, Type? targetType, object? parameter, CultureInfo? culture) => value is string stringValue ? !string.IsNullOrWhiteSpace(stringValue) : throw new InvalidArgumentException("Binding must be of type string");

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

Usage Syntax

XAML Usage

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
             x:Class="MyLittleApp.MainPage">

    <ContentPage.Resources>
        <ResourceDictionary>
            <xct: IsStringNullOrWhiteSpaceConverter x:Key="IsStringNullOrWhiteSpaceConverter" />
        </ResourceDictionary>
    </ContentPage.Resources>

    <StackLayout>

        <Label IsVisible="{Binding MyStringValue, Converter={StaticResource IsStringNullOrWhiteSpaceConverter}}" />

    </StackLayout>
</ContentPage>

C# Usage

class MyPage : ContentPage
{
  public MyPage()
  {
    Content = new StackLayout
    {
      Children = 
      {
          new Label().Bind(Label.IsVisibleProperty, nameof(ViewModel.MyString), converter: new IsStringNullOrWhiteSpaceConverter()),
      };
    }
  }
}