BindableProperty XamarinForms

XamarinFormsBindableProperty.cs

public static readonly BindableProperty FoobarProperty=BindableProperty.Create<YourClass, bool>( p => p.Foobar, false );

public bool Foobar
{
	get 
	{ 
		return (bool)GetValue(FoobarProperty); 
	}
	set 
	{
		SetValue(FoobarProperty, value); 
	}
}

protected override void OnPropertyChanged(string propertyName)
{
	base.OnPropertyChanged(propertyName);

	switch( propertyName )
	{
		case "Foobar":
			UpdateFoobar();
			break;
	}
}

private void UpdateFoobar()
{
	// Do whatever you need to do when the property 
	// has been set here. By the time this method is
	// called Foobar will already hold the updated value
	// so if you need to reference the old value you will
	// need to store it in a class variable
}