// Apply two sourcemodifiers to the input source: One to provide resistance, one to stop motion
public void SetupPullToRefreshBehavior(
float pullToRefreshDistance)
{
//
// Modifier 1: Cut DeltaY to a third as long as the InteractionTracker is not yet at the
// pullRefreshDistance.
//
CompositionConditionalValue resistanceModifier = CompositionConditionalValue.Create(_compositor);
ExpressionAnimation resistanceCondition = _compositor.CreateExpressionAnimation(
$"-tracker.Position.Y < {pullToRefreshDistance}");
resistanceCondition.SetReferenceParameter("tracker", _tracker);
ExpressionAnimation resistanceAlternateValue = _compositor.CreateExpressionAnimation(
"source.DeltaPosition.Y / 3");
resistanceAlternateValue.SetReferenceParameter("source", _interactionSource);
resistanceModifier.Condition = resistanceCondition;
resistanceModifier.Value = resistanceAlternateValue;
//
// Modifier 2: Zero the delta if we are past the pullRefreshDistance. (So we can't pan
// past the pullRefreshDistance)
//
CompositionConditionalValue stoppingModifier = CompositionConditionalValue.Create(_compositor);
ExpressionAnimation stoppingCondition = _compositor.CreateExpressionAnimation(
$"-tracker.Position.Y >= {pullToRefreshDistance}");
stoppingCondition.SetReferenceParameter("tracker", _tracker);
ExpressionAnimation stoppingAlternateValue = _compositor.CreateExpressionAnimation("0");
stoppingModifier.Condition = stoppingCondition;
stoppingModifier.Value = stoppingAlternateValue;
//
// Apply the modifiers to the source as a list
//
List <CompositionConditionalValue> modifierList =
new List <CompositionConditionalValue>()
{
resistanceModifier, stoppingModifier
};
_interactionSource.ConfigureDeltaPositionYModifiers(modifierList);
}
private void MainPage_Loaded(object sender, RoutedEventArgs e)
{
ThumbnailList.ItemsSource = new List <Item>
{
new Item {
Name = "Daren"
},
new Item {
Name = "Kendra"
},
new Item {
Name = "Gavin"
},
new Item {
Name = "Naia"
},
new Item {
Name = "Frodo"
},
new Item {
Name = "Stella"
},
new Item {
Name = "DJ"
},
new Item {
Name = "Stasch"
}
};
// InteractionTracker and VisualInteractionSource setup.
_root = ElementCompositionPreview.GetElementVisual(Root);
_contentPanelVisual = ElementCompositionPreview.GetElementVisual(ContentPanel);
_compositor = _root.Compositor;
_tracker = InteractionTracker.Create(_compositor);
_interactionSource = VisualInteractionSource.Create(_root);
_interactionSource.PositionYSourceMode = InteractionSourceMode.EnabledWithInertia;
_interactionSource.PositionYChainingMode = InteractionChainingMode.Always;
_tracker.InteractionSources.Add(_interactionSource);
var refreshPanelHeight = (float)RefreshPanel.ActualHeight;
_tracker.MaxPosition = new Vector3((float)Root.ActualWidth, 0, 0);
_tracker.MinPosition = new Vector3(-(float)Root.ActualWidth, -refreshPanelHeight, 0);
// Use the Tacker's Position (negated) to apply to the Offset of the Image.
// The -{refreshPanelHeight} is to hide the refresh panel
m_positionExpression =
_compositor.CreateExpressionAnimation($"-tracker.Position.Y - {refreshPanelHeight} ");
m_positionExpression.SetReferenceParameter("tracker", _tracker);
_contentPanelVisual.StartAnimation("Offset.Y", m_positionExpression);
var resistanceModifier = CompositionConditionalValue.Create(_compositor);
var resistanceCondition = _compositor.CreateExpressionAnimation(
$"-tracker.Position.Y < {pullToRefreshDistance}");
resistanceCondition.SetReferenceParameter("tracker", _tracker);
var resistanceAlternateValue = _compositor.CreateExpressionAnimation(
"source.DeltaPosition.Y / 3");
resistanceAlternateValue.SetReferenceParameter("source", _interactionSource);
resistanceModifier.Condition = resistanceCondition;
resistanceModifier.Value = resistanceAlternateValue;
var stoppingModifier = CompositionConditionalValue.Create(_compositor);
var stoppingCondition = _compositor.CreateExpressionAnimation(
$"-tracker.Position.Y >= {pullToRefreshDistance}");
stoppingCondition.SetReferenceParameter("tracker", _tracker);
var stoppingAlternateValue = _compositor.CreateExpressionAnimation("0");
stoppingModifier.Condition = stoppingCondition;
stoppingModifier.Value = stoppingAlternateValue;
//Now add the 2 source modifiers to the InteractionTracker.
var modifierList = new List <CompositionConditionalValue> {
resistanceModifier, stoppingModifier
};
_interactionSource.ConfigureDeltaPositionYModifiers(modifierList);
//The PointerPressed handler needs to be added using AddHandler method with the //handledEventsToo boolean set to "true"
//instead of the XAML element's "PointerPressed=Window_PointerPressed",
//because the list view needs to chain PointerPressed handled events as well.
ContentPanel.AddHandler(PointerPressedEvent, new PointerEventHandler(Window_PointerPressed), true);
}
