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using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
{
/// <summary>A watcher which detects changes to an observable collection.</summary>
/// <typeparam name="TValue">The value type within the collection.</typeparam>
internal class ObservableCollectionWatcher<TValue> : BaseDisposableWatcher, ICollectionWatcher<TValue>
{
/*********
** Fields
*********/
/// <summary>The field being watched.</summary>
private readonly ObservableCollection<TValue> Field;
/// <summary>The pairs added since the last reset.</summary>
private readonly List<TValue> AddedImpl = new();
/// <summary>The pairs removed since the last reset.</summary>
private readonly List<TValue> RemovedImpl = new();
/// <summary>The previous values as of the last update.</summary>
private readonly List<TValue> PreviousValues = new();
/*********
** Accessors
*********/
/// <inheritdoc />
public bool IsChanged => this.AddedImpl.Count > 0 || this.RemovedImpl.Count > 0;
/// <inheritdoc />
public IEnumerable<TValue> Added => this.AddedImpl;
/// <inheritdoc />
public IEnumerable<TValue> Removed => this.RemovedImpl;
/*********
** Public methods
*********/
/// <summary>Construct an instance.</summary>
/// <param name="field">The field to watch.</param>
public ObservableCollectionWatcher(ObservableCollection<TValue> field)
{
this.Field = field;
field.CollectionChanged += this.OnCollectionChanged;
}
/// <inheritdoc />
public void Update()
{
this.AssertNotDisposed();
}
/// <inheritdoc />
public void Reset()
{
this.AssertNotDisposed();
this.AddedImpl.Clear();
this.RemovedImpl.Clear();
}
/// <inheritdoc />
public override void Dispose()
{
if (!this.IsDisposed)
this.Field.CollectionChanged -= this.OnCollectionChanged;
base.Dispose();
}
/*********
** Private methods
*********/
/// <summary>A callback invoked when an entry is added or removed from the collection.</summary>
/// <param name="sender">The event sender.</param>
/// <param name="e">The event arguments.</param>
private void OnCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Reset)
{
this.RemovedImpl.AddRange(this.PreviousValues);
this.PreviousValues.Clear();
}
else
{
TValue[]? added = e.NewItems?.Cast<TValue>().ToArray();
TValue[]? removed = e.OldItems?.Cast<TValue>().ToArray();
if (removed != null)
{
this.RemovedImpl.AddRange(removed);
this.PreviousValues.RemoveRange(e.OldStartingIndex, removed.Length);
}
if (added != null)
{
this.AddedImpl.AddRange(added);
this.PreviousValues.InsertRange(e.NewStartingIndex, added);
}
}
}
}
}
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