Xamarin Forms - negate bool binding values

Question

I am learning the xamarin forms and mvvm pattern. I am wondering, if is it possible to negate binding bool value. What I mean is:

I have, let's say Entry with isVisible Binding:

<Entry
    x:Name="TextEntry"
    IsVisible="{Binding IsVisibleEntry}"
/>

and Label which i want to hide when TextEntry is visible.

<Label x:Name="MainLabel" 
       isVisible="!{Binding IsVisibleEntry}"/> //ofc it is not working

Is it possible to do without making a new variable for MainLabel in ViewModel?

Answer 1

Option One: Converter

Define the converter:

    public class InverseBoolConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return !((bool)value);
        }
    
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return value;
            //throw new NotImplementedException();
        }
    }

Usage in XAML:

    <Label x:Name="MainLabel" 
           isVisible="{Binding IsVisibleEntry, Converter={Helpers:InverseBoolConverter}}"/>

XAML Header

    xmlns:Helpers="clr-namespace:HikePOS.Helpers"

Option Two: Trigger

    <Label x:Name="MainLabel" isVisible="{Binding IsVisibleEntry}">
        <Label.Triggers>
            <DataTrigger TargetType="Label" Binding="{Binding IsVisibleEntry}" Value="True">
                <Setter Property="IsVisible" Value="False" />
            </DataTrigger>
        </Label.Triggers>
    </Label>

Answer 2

You will need to create an Invert converter so your binding would look somewhat like this:

public class InverseBoolConverter : IValueConverter
{
    public object Convert (object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return !(bool)value;
    }
    public object ConvertBack (object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return !(bool)value;
    }
}

In your XAML

<local:InverseBoolConverter x:Key="inverter"/>
<Entry
x:Name="TextEntry"
IsVisible="{Binding IsVisibleEntry, Converter={StaticResource inverter}}"
/>

Answer 3

Instead of writing your own converter, you could use Xamarin Community Toolkit which now has a converter invertedboolconverter that can be used out of the box. This example (taken from Microsoft's documentation) shows how it works:

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

    <StackLayout>

        <Label IsVisible="{Binding MyBooleanValue, Converter={StaticResource InvertedBoolConverter}}" />

    </StackLayout>
</ContentPage>