IsNotNullConverter

Article
03/01/2023

The IsNotNullConverter is a one way converter that converts Object? to a bool value.

The Convert method returns false when the binded object is null or true otherwise.

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

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 IsNotNullConverter

The IsNotNullConverter 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.IsNotNullConverterPage">

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

    <Label Text="Object is not null"
           IsVisible="{Binding MyObject, Converter={StaticResource IsNotNullConverter}}" />

</ContentPage>

C#

The IsNotNullConverter can be used as follows in C#:


class IsNotNullConverterPage : ContentPage
{
    public IsNotNullConverterPage()
    {
        var label = new Label { Text = "Object is not null" };

		label.SetBinding(
			Label.IsVisibleProperty,
			new Binding(nameof(ViewModels.MyObject), converter: new IsNotNullConverter()));

		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 IsNotNullConverterPage : ContentPage
{
    public IsNotNullConverterPage()
    {
        Content = new Label { Text = "Object is not null" }
            .Bind(
                Label.IsVisibleProperty,
                static (ViewModel vm) => vm.MyObject,
                converter: new IsNotNullConverter());
    }
}

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

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