添加对 Core 的直接引用

RhythmBaseCore/Exceptions/IllegalBeatException.cs

@@ -0,0 +1,25 @@
+using RhythmBase.Events;
+namespace RhythmBase.Exceptions
+{
+	/// <summary>
+	/// Exception thrown when a beat is placed in an illegal position.
+	/// </summary>
+	public class IllegalBeatException(IBarBeginningEvent item) : RhythmBaseException
+	{
+		/// <summary>
+		/// Gets the error message that explains the reason for the exception.
+		/// </summary>
+		public override string Message
+		{
+			get
+			{
+				return string.Format("This beat is invalid, the event {0} only allows the beat to be at the beginning of the bar.", ((BaseEvent)Item).Type);
+			}
+		}
+
+		/// <summary>
+		/// Gets the event that caused the exception.
+		/// </summary>
+		public IBarBeginningEvent Item = item;
+	}
+}