34 lines
963 B
C#
34 lines
963 B
C#
namespace DeclarativeProperty;
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public sealed class DistinctUntilChangedProperty<T> : DeclarativePropertyBase<T>
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{
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private readonly Func<T?, T?, bool>? _comparer;
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private bool _firstFire = true;
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public DistinctUntilChangedProperty(IDeclarativeProperty<T> from, Func<T?, T?, bool>? comparer = null) : base(from.Value)
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{
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_comparer = comparer;
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AddDisposable(from.Subscribe(Handle));
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}
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private Task Handle(T next, CancellationToken cancellationToken = default)
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{
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if (_comparer is { } comparer)
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{
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if (comparer(Value, next))
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{
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return Task.CompletedTask;
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}
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}
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else if (
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(next is null && Value is null && !_firstFire)
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|| (Value?.Equals(next) ?? false)
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)
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{
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return Task.CompletedTask;
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}
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_firstFire = false;
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return SetNewValueAsync(next, cancellationToken);
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}
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} |