[Proposal] IsStringNullOrEmpty Converters

[brminnick]

IsStringNullOrEmptyConverter

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

Summary

The IsStringNullOrEmptyConverter 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.IsNullOrEmpty.

The IsStringNotNullOrEmptyConverter 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.IsNullOrEmpty.

Detailed Design

IsStringNullOrEmptyConverter.shared.cs

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

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

IsStringNotNullOrEmptyConverter.shared.cs

public class IsStringNullOrEmptyConverter : ValueConverterExtension, ICommunityToolkitValueConverter
{
  public object Convert(object? value, Type? targetType, object? parameter, CultureInfo? culture) => value is string stringValue ? !string.IsNullOrEmpty(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: IsStringNullOrEmptyConverter x:Key="IsStringNullOrEmptyConverter" />
        </ResourceDictionary>
    </ContentPage.Resources>

    <StackLayout>

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

    </StackLayout>
</ContentPage>

C# Usage

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

[juansturla]

Hi again! I added the ViewModel for this sample on #132 PR, so the only thing left is modifying the XAML. I can do that if you like :)

[steven62f]

Hi! I want to help with the sample :)

[juansturla]

Well it looks like you already did that before being assigned hahaha

[brminnick]

Thanks @StevenHanquez! It is assigned to you.

[ghost]

Reopening Proposal.

Only Proposals moved to the Closed Project Column and Completed Project Column can be closed.