WPF Trigger not working, what am i doing wrong?

Question

I have the following code (only relevant snippets)

Answer 1

UIElement.IsVisible is not a mutable property. You'll have to set UIElement.Visibility, which is an enum.

The reason why you get an exception is because FrameworkElement.Triggers only accepts EventTrigger. This means that if you do UIElement.Triggers (Button.Triggers or ribbon:RibbonToggleButton.Triggers), you can only add EventTriggers under that. Style, DataTemplate and ControlTemplate accept all TriggerBase derived classes.

Edit

As Mackho pointed out, you cannot use TargetName under Style. You'd have to accomplish this using data binding.

Assuming SPanel1 is a StackPanel, here's what you can do:

Create a converter

public class BoolToVisibilityConverter : IValueConverter {
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        return (bool)value ? Visibility.Visible : Visibility.Collapsed;
    }
    public object ConvertBack(object value, Type targetType,  object parameter, CultureInfo culture)
    {
        return null;
    }
}

Somewhere in the root control's resources, add BoolToVisibilityConverter

Add x:Name to your toggle button; lets say you call it "MyToggleButton"

<StackPanel x:Name="SPanel1" ...
            Visibility="{Binding IsChecked, ElementName=MyToggleButton, Converter={StaticResource BoolToVisibilityConverter}}" />

And do something very similar for SPanel2.

Answer 2

You need to use DataTrigger, and set the style property of the two panels to the IsChecked propery of the checkbox, here an example

        <CheckBox Name="check" Content="Prova" IsChecked="True"> </CheckBox>

        <Canvas Name="SPanel1" Background="Blue" Width="100" Height="100">
            <Canvas.Style>
                <Style TargetType="Canvas">
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding ElementName=check, Path=IsChecked}" Value="True">
                             <Setter Property="Visibility" Value="Hidden"></Setter>
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </Canvas.Style>
        </Canvas>