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osu-lazer/osu.Game/Screens/Select/Carousel/CarouselGroupEagerSelect.cs

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// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.
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using System;
using System.Linq;
namespace osu.Game.Screens.Select.Carousel
{
/// <summary>
/// A group which ensures at least one child is selected (if the group itself is selected).
/// </summary>
public class CarouselGroupEagerSelect : CarouselGroup
{
public CarouselGroupEagerSelect()
{
State.ValueChanged += state =>
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{
if (state.NewValue == CarouselItemState.Selected)
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attemptSelection();
};
}
/// <summary>
/// The last selected item.
/// </summary>
protected CarouselItem LastSelected { get; private set; }
/// <summary>
/// We need to keep track of the index for cases where the selection is removed but we want to select a new item based on its old location.
/// </summary>
private int lastSelectedIndex;
/// <summary>
/// To avoid overhead during filter operations, we don't attempt any selections until after all
/// children have been filtered. This bool will be true during the base <see cref="Filter(FilterCriteria)"/>
/// operation.
/// </summary>
private bool filteringChildren;
public override void Filter(FilterCriteria criteria)
{
filteringChildren = true;
base.Filter(criteria);
filteringChildren = false;
attemptSelection();
}
public override void RemoveChild(CarouselItem i)
{
base.RemoveChild(i);
if (i != LastSelected)
updateSelectedIndex();
}
public override void AddChild(CarouselItem i)
{
base.AddChild(i);
attemptSelection();
}
protected override void ChildItemStateChanged(CarouselItem item, CarouselItemState value)
{
base.ChildItemStateChanged(item, value);
switch (value)
{
case CarouselItemState.Selected:
updateSelected(item);
break;
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case CarouselItemState.NotSelected:
case CarouselItemState.Collapsed:
attemptSelection();
break;
}
}
private void attemptSelection()
{
if (filteringChildren) return;
// we only perform eager selection if we are a currently selected group.
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if (State.Value != CarouselItemState.Selected) return;
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// we only perform eager selection if none of our children are in a selected state already.
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if (Children.Any(i => i.State.Value == CarouselItemState.Selected)) return;
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PerformSelection();
}
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protected virtual CarouselItem GetNextToSelect()
{
return Children.Skip(lastSelectedIndex).FirstOrDefault(i => !i.Filtered.Value) ??
Children.Reverse().Skip(InternalChildren.Count - lastSelectedIndex).FirstOrDefault(i => !i.Filtered.Value);
}
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protected virtual void PerformSelection()
{
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CarouselItem nextToSelect = GetNextToSelect();
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if (nextToSelect != null)
nextToSelect.State.Value = CarouselItemState.Selected;
else
updateSelected(null);
}
private void updateSelected(CarouselItem newSelection)
{
if (newSelection != null)
LastSelected = newSelection;
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updateSelectedIndex();
}
private void updateSelectedIndex() => lastSelectedIndex = LastSelected == null ? 0 : Math.Max(0, InternalChildren.IndexOf(LastSelected));
}
}