BooleanToVisibilityConverter

Idea was to have one rectangle and on button click do hide / show that rectangle. Easiest way is with BooleanToVisibilityConverter.

XAML looks like this:

<Window x:Class="BooleanToVisibilityConverterExample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:viewModel="clr-namespace:BooleanToVisibilityConverterExample.ViewModel"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.Resources>
            <viewModel:BooleanToVisibilityConverterExampleViewModel x:Key="BooleanToVisibilityConverterExampleViewModel" />
            <BooleanToVisibilityConverter x:Key="BoolToVis" />
        </Grid.Resources>
        
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="30" />
        </Grid.RowDefinitions>
        
        <Button DataContext="{StaticResource BooleanToVisibilityConverterExampleViewModel}" Command="{Binding OnClick}" Grid.Row="1" Content="Click Me!" VerticalContentAlignment="Bottom"/>

        <Rectangle x:Name="greenLine"
                    Height="25"
                    Width="25"
                    DataContext="{StaticResource BooleanToVisibilityConverterExampleViewModel}"
                    Visibility="{Binding MyHidden, Converter={StaticResource BoolToVis}, UpdateSourceTrigger=PropertyChanged}"
                    Fill="Green"/>
    </Grid>
</Window>

Note how I declared resource:

<BooleanToVisibilityConverter x:Key="BoolToVis" />

After that in rectangle declaration note:

Visibility="{Binding MyHidden, Converter={StaticResource BoolToVis}, UpdateSourceTrigger=PropertyChanged}"

There is no too much philosophy about code itself, basically everything is happening here:

MyHidden = !MyHidden;
OnPropertyChanged("MyHidden");

Property changed I explained here.

Example you can download from here.

There is also another solution, which I will not explain, since it is a bit more complicated, you have to implement IValueConverter, example for that version you can download from here, and to write that example I was this web site.