rkusa

var observable = Observable.GenerateWithTime(0, x => x < yourListBox.Items.Count, x => x, x => TimeSpan.FromMilliseconds(50), x => x + 1);

observable.Subscribe(i => Dispatcher.BeginInvoke(() =>
	VisualStateManager.GoToState(
		(ListBoxItem)yourListBox.ItemContainerGenerator
			.ContainerFromIndex(i), "AfterLoaded", true)));

rkusa

GeneralTransform elementTransform = element.TransformToVisual(container);
Rect rect = elementTransform.TransformBounds(new Rect(new Point(0, 0), element.RenderSize));
rect.Intersect(new Rect(new Point(0, 0), MainListBox.RenderSize));

return rect != Rect.Empty;

rkusa

_firstInViewport = 0;
_lastInViewport = MainListBox.Items.Count - 1;

// determine first visible item
for (int i = 0; i < MainListBox.Items.Count; i++)
{
	ListBoxItem item = (ListBoxItem)MainListBox.ItemContainerGenerator.ContainerFromIndex(i);
	if (item == null || !IsVisibleInViewPort(item, MainListBox))
		continue;

rkusa

var observable = Observable.GenerateWithTime(_firstInViewport, x => x <= _lastInViewport, x => x,
                                             x => TimeSpan.FromMilliseconds(50), x => x + 1);
observable.Subscribe(i => Dispatcher.BeginInvoke(() =>
	VisualStateManager.GoToState(
		(ListBoxItem)MainListBox.ItemContainerGenerator
			.ContainerFromIndex(i), "AfterLoaded", true)));

rkusa

for (int i = _firstInViewport; i <= _lastInViewport; i++)
{
	ListBoxItem item = (ListBoxItem)MainListBox.ItemContainerGenerator.ContainerFromIndex(i);
	if (item == null)
		continue;

	VisualStateManager.GoToState(item, "BeforeLoaded", false);
}

rkusa

<toolkit:PickerBox ItemsSource="{Binding FirstItems}" SelectedItem="{Binding FirstSelected}"
		   Foreground="{StaticResource PhoneContrastForegroundBrush}"
		   FontSize="36" Margin="0,0,0,48" />

rkusa

<toolkit:PickerBox ItemsSource="{Binding SecondItems}" SelectedItem="{Binding SecondSelected}" Foreground="{StaticResource PhoneContrastForegroundBrush}">
	<toolkit:PickerBox.ItemTemplate>
		<DataTemplate>
			<StackPanel x:Name="stackPanel" Orientation="Horizontal" Margin="10,10" Width="440">
				<Rectangle Fill="{Binding Brush}" Width="42" Height="42" />
				<TextBlock Text="{Binding Name}" FontSize="36" VerticalAlignment="Center" Margin="25,0,0,0" />
			</StackPanel>
		</DataTemplate>
	</toolkit:PickerBox.ItemTemplate>
</toolkit:PickerBox>

rkusa

<Style TargetType="controls:PickerBox">
	<Setter Property="Template">
		<Setter.Value>
			<ControlTemplate TargetType="controls:PickerBox">
				<StackPanel>
					<VisualStateManager.VisualStateGroups>
						<VisualStateGroup x:Name="ButtonStates">
							<VisualStateGroup.Transitions>
								<VisualTransition GeneratedDuration="0:0:0.1"/>
							</VisualStateGroup.Transitions>

rkusa

MainListBox.ItemContainerGenerator.ItemsChanged += ItemContainerGenerator_ItemsChanged;

rkusa

private void ItemContainerGenerator_ItemsChanged(object sender, ItemsChangedEventArgs e)
{
	Dispatcher.BeginInvoke(new ItemAddedDelegate(i =>
	{
		var item = (ListBoxItem) MainListBox.ItemContainerGenerator.ContainerFromIndex(i - 1);
		if (item == null)
			return;

		VisualStateManager.GoToState(item, "BeforeLoaded", false);
		item.Opacity = 1.0;