is-string-null-or-whitespace-converter.md

title	author	description	ms.date
IsStringNullOrWhiteSpaceConverter - .NET MAUI Community Toolkit	bijington	The IsStringNullOrWhiteSpaceConverter is a one way converter that returns a bool indicating whether the binding value is null or string.Empty or contains whitespace characters only.	03/30/2022

IsStringNullOrWhiteSpaceConverter

The IsStringNullOrWhiteSpaceConverter is a one way converter that returns a bool indicating whether the binding value is null, string.Empty or contains whitespace characters only.

The Convert method returns true when the binding value is null, string.Empty or contains whitespace characters only.

The ConvertBack method is not supported. For the opposite behavior see the IsStringNotNullOrWhiteSpaceConverter.

[!INCLUDE common converter properties]

Syntax

XAML

Including the XAML namespace

[!INCLUDE XAML usage guidance]

Using the IsStringNullOrWhitespaceConverter

The IsStringNullOrWhiteSpaceConverter can be used as follows in XAML:

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"
             x:Class="CommunityToolkit.Maui.Sample.Pages.Converters.IsStringNullOrWhiteSpaceConverterPage">

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

    <Label Text="A value is required"
           IsVisible="{Binding MyValue, Converter={StaticResource IsStringNullOrWhiteSpaceConverter}}" />

</ContentPage>

C#

The IsStringNullOrWhiteSpaceConverter can be used as follows in C#:

class IsStringNullOrWhiteSpaceConverterPage : ContentPage
{
    public IsStringNullOrWhiteSpaceConverterPage()
    {
        var label = new Label { Text = "A value is required" };

		label.SetBinding(
			Label.IsVisibleProperty,
			new Binding(
				nameof(ViewModels.MyValue),
				converter: new IsStringNullOrWhiteSpaceConverter()));

		Content = label;
    }
}

C# Markup

Our CommunityToolkit.Maui.Markup package provides a much more concise way to use this converter in C#.

using CommunityToolkit.Maui.Markup;

class IsStringNullOrWhiteSpaceConverterPage : ContentPage
{
    public IsStringNullOrWhiteSpaceConverterPage()
    {
        Content = new Label { Text = "A value is required" }
            .Bind(
                Label.IsVisibleProperty,
                static (ViewModel vm) => vm.MyValue,
                converter: new IsStringNullOrWhiteSpaceConverter());
    }
}

Examples

You can find an example of this converter in action in the .NET MAUI Community Toolkit Sample Application.

API

You can find the source code for IsStringNullOrWhiteSpaceConverter over on the .NET MAUI Community Toolkit GitHub repository.