IsStringNullOrEmptyConverter

Article
03/01/2023

The IsStringNullOrEmptyConverter is a one way converter that returns a bool indicating whether the binding value is null or string.Empty.

The Convert method returns true when the binding value is null or string.Empty.

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

BaseConverter Properties

The following properties are implemented in the base class, public abstract class BaseConverter:

Property	Description
`DefaultConvertReturnValue`	Default value to return when `IValueConverter.Convert(object?, Type, object?, CultureInfo?)` throws an `Exception`. This value is used when CommunityToolkit.Maui.Options`.ShouldSuppressExceptionsInConverters` is set to `true`.
`DefaultConvertBackReturnValue`	Default value to return when `IValueConverter.ConvertBack(object?, Type, object?, CultureInfo?)` throws an `Exception`. This value is used when CommunityToolkit.Maui.Options`.ShouldSuppressExceptionsInConverters` is set to `true`.

ICommunityToolkitValueConverter Properties

The following properties are implemented in the public interface ICommunityToolkitValueConverter:

Property	Type	Description
`DefaultConvertReturnValue`	`object?`	Default value to return when `IValueConverter.Convert(object?, Type, object?, CultureInfo?)` throws an `Exception`. This value is used when CommunityToolkit.Maui.Options`.ShouldSuppressExceptionsInConverters` is set to `true`.
`DefaultConvertBackReturnValue`	`object?`	Default value to return when `IValueConverter.ConvertBack(object?, Type, object?, CultureInfo?)` throws an `Exception`. This value is used when CommunityToolkit.Maui.Options`.ShouldSuppressExceptionsInConverters` is set to `true`.

Syntax

XAML

Including the XAML namespace

In order to use the toolkit in XAML the following xmlns needs to be added into your page or view:

xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"

Therefore the following:

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

</ContentPage>

Would be modified to include the xmlns as follows:

<ContentPage
    x:Class="CommunityToolkit.Maui.Sample.Pages.MyPage"
    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">

</ContentPage>

Using the IsStringNullOrEmptyConverter

The IsStringNullOrEmptyConverter 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.IsStringNullOrEmptyConverterPage">

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

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

</ContentPage>

C#

The IsStringNullOrEmptyConverter can be used as follows in C#:

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

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

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

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 IsStringNullOrEmptyConverter over on the .NET MAUI Community Toolkit GitHub repository.

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