/// <summary>
/// Scrolls to the desired index, starting from the provided visual item.
/// </summary>
/// <param name="item">The visual item to start from.</param>
/// <param name="to">The target index to scroll to.</param>
private void ScrollToIndex(LoopingListItem item, int to)
{
if (!this.IsInitialized())
{
return;
}
int from = item.LogicalIndex;
if (item.LogicalIndex == to)
{
this.BringIntoView(to);
return;
}
int indexOffset = Math.Abs(from - to);
int pivotIndex = this.logicalCount / 2;
int sign = Math.Sign(from - to);
if (indexOffset > pivotIndex)
{
indexOffset = this.logicalCount - indexOffset;
sign *= -1;
}
double offset = this.visualOffset + (sign * indexOffset * this.itemLength);
this.scrollState = LoopingPanelScrollState.ScrollingToIndex;
this.AnimateVerticalOffset(offset);
}
/// <summary>
/// Ensures that the visual item, associated with the specified logical index is currently displayed.
/// </summary>
/// <param name="logicalIndex"></param>
/// <param name="animate">True to perform animated scrolling, false otherwise.</param>
private void BringIntoView(int logicalIndex, bool animate)
{
// no visual children yet
if (this.items.Count == 0)
{
return;
}
if (logicalIndex < 0 || logicalIndex >= this.logicalCount)
{
return;
}
double offset = this.CalculateOffset(logicalIndex);
if (animate)
{
this.scrollState = LoopingPanelScrollState.ScrollingToIndex;
this.AnimateVerticalOffset(offset);
}
else
{
this.UpdateWheel(offset, false);
}
}
/// <summary>
/// Applies the specified offset as current.
/// </summary>
/// <param name="offset">The desired offset.</param>
/// <param name="duration">The duration of the animation used to apply the offset.</param>
/// <param name="ease">The easing function that describes animation interpolation.</param>
internal void SetVerticalOffset(double offset, Duration duration, EasingFunctionBase ease)
{
if (!this.IsInitialized())
{
return;
}
this.scrollState = LoopingPanelScrollState.Scrolling;
this.AnimateVerticalOffset(duration, ease, offset);
}
/// <summary>
/// Stops the vertical offset animation (if running).
/// </summary>
internal void StopOffsetAnimation(bool raiseCompleted)
{
LoopingPanelScrollState currentState = this.scrollState;
this.scrollState = LoopingPanelScrollState.NotScrolling;
this.animating = false;
this.offsetStoryboard.Stop();
if (raiseCompleted && currentState != LoopingPanelScrollState.NotScrolling)
{
this.OnScrollCompleted(currentState);
}
}
private void OnOffsetAnimationCompleted(object sender, object args)
{
if (this.scrollState == LoopingPanelScrollState.NotScrolling)
{
return;
}
LoopingPanelScrollState previousState = this.scrollState;
this.animating = false;
this.offsetStoryboard.Stop();
this.OnScrollCompleted(previousState);
}
internal void Scroll(double amount)
{
if (!this.IsInitialized())
{
return;
}
if (this.animating)
{
this.StopOffsetAnimation(false);
}
this.scrollState = LoopingPanelScrollState.Scrolling;
this.UpdateWheel(this.visualOffset + amount, false);
}
/// <summary>
/// Notifies that a scroll operation has completed.
/// </summary>
/// <param name="previousState">The state the panel was in before the scrolling ended.</param>
private void OnScrollCompleted(LoopingPanelScrollState previousState)
{
this.scrollState = LoopingPanelScrollState.NotScrolling;
if (!this.isCentered)
{
return;
}
if (previousState == LoopingPanelScrollState.Scrolling ||
previousState == LoopingPanelScrollState.ScrollingToIndex)
{
this.CenterMiddleItem(previousState != LoopingPanelScrollState.ScrollingToIndex, true);
}
}
/// <summary>
/// Ensures that the visual item, associated with the specified logical index is currently displayed.
/// </summary>
/// <param name="logicalIndex">The logical index of the item.</param>
/// <param name="visualIndex">The visual index of the item.</param>
/// <param name="animate">True to perform animated scrolling, false otherwise.</param>
private void BringIntoView(int logicalIndex, int visualIndex, bool animate)
{
// no visual children yet
if (this.items.Count == 0)
{
return;
}
if (logicalIndex < 0 || logicalIndex >= this.logicalCount)
{
return;
}
double offset;
if (this.IsIndexInView(logicalIndex) && visualIndex >= 0)
{
offset = this.CalculateVisualOffset(visualIndex, this.visualIndexChain[0]);
}
else
{
offset = this.CalculateLogicalOffset(logicalIndex, this.topLogicalIndex);
}
if (animate)
{
this.scrollState = LoopingPanelScrollState.ScrollingToIndex;
this.AnimateVerticalOffset(offset);
}
else
{
this.UpdateWheel(offset, false);
this.UpdateLayout();
// Force items to be remeasured as occasionalli there is no measure for items and they desapear.
this.InvalidateMeasure();
}
}
