levelcollection.cs

详细讲述了数据库编程

#region Copyright & License
//
// Copyright 2001-2005 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System;
using System.Collections;

namespace log4net.Core
{
	/// <summary>
	/// A strongly-typed collection of <see cref="Level"/> objects.
	/// </summary>
	/// <author>Nicko Cadell</author>
	public class LevelCollection : ICollection, IList, IEnumerable, ICloneable
	{
		#region Interfaces

		/// <summary>
		/// Supports type-safe iteration over a <see cref="LevelCollection"/>.
		/// </summary>
		public interface ILevelCollectionEnumerator
		{
			/// <summary>
			/// Gets the current element in the collection.
			/// </summary>
			Level Current { get; }

			/// <summary>
			/// Advances the enumerator to the next element in the collection.
			/// </summary>
			/// <returns>
			/// <c>true</c> if the enumerator was successfully advanced to the next element; 
			/// <c>false</c> if the enumerator has passed the end of the collection.
			/// </returns>
			/// <exception cref="InvalidOperationException">
			/// The collection was modified after the enumerator was created.
			/// </exception>
			bool MoveNext();

			/// <summary>
			/// Sets the enumerator to its initial position, before the first element in the collection.
			/// </summary>
			void Reset();
		}

		#endregion

		private const int DEFAULT_CAPACITY = 16;

		#region Implementation (data)

		private Level[] m_array;
		private int m_count = 0;
		private int m_version = 0;

		#endregion
	
		#region Static Wrappers

		/// <summary>
		/// Creates a read-only wrapper for a <c>LevelCollection</c> instance.
		/// </summary>
		/// <param name="list">list to create a readonly wrapper arround</param>
		/// <returns>
		/// A <c>LevelCollection</c> wrapper that is read-only.
		/// </returns>
		public static LevelCollection ReadOnly(LevelCollection list)
		{
			if(list==null) throw new ArgumentNullException("list");

			return new ReadOnlyLevelCollection(list);
		}

		#endregion

		#region Constructors

		/// <summary>
		/// Initializes a new instance of the <c>LevelCollection</c> class
		/// that is empty and has the default initial capacity.
		/// </summary>
		public LevelCollection()
		{
			m_array = new Level[DEFAULT_CAPACITY];
		}
		
		/// <summary>
		/// Initializes a new instance of the <c>LevelCollection</c> class
		/// that has the specified initial capacity.
		/// </summary>
		/// <param name="capacity">
		/// The number of elements that the new <c>LevelCollection</c> is initially capable of storing.
		/// </param>
		public LevelCollection(int capacity)
		{
			m_array = new Level[capacity];
		}

		/// <summary>
		/// Initializes a new instance of the <c>LevelCollection</c> class
		/// that contains elements copied from the specified <c>LevelCollection</c>.
		/// </summary>
		/// <param name="c">The <c>LevelCollection</c> whose elements are copied to the new collection.</param>
		public LevelCollection(LevelCollection c)
		{
			m_array = new Level[c.Count];
			AddRange(c);
		}

		/// <summary>
		/// Initializes a new instance of the <c>LevelCollection</c> class
		/// that contains elements copied from the specified <see cref="Level"/> array.
		/// </summary>
		/// <param name="a">The <see cref="Level"/> array whose elements are copied to the new list.</param>
		public LevelCollection(Level[] a)
		{
			m_array = new Level[a.Length];
			AddRange(a);
		}

		/// <summary>
		/// Initializes a new instance of the <c>LevelCollection</c> class
		/// that contains elements copied from the specified <see cref="Level"/> collection.
		/// </summary>
		/// <param name="col">The <see cref="Level"/> collection whose elements are copied to the new list.</param>
		public LevelCollection(ICollection col)
		{
			m_array = new Level[col.Count];
			AddRange(col);
		}
		
		/// <summary>
		/// Type visible only to our subclasses
		/// Used to access protected constructor
		/// </summary>
		protected internal enum Tag 
		{
			/// <summary>
			/// A value
			/// </summary>
			Default
		}

		/// <summary>
		/// Allow subclasses to avoid our default constructors
		/// </summary>
		/// <param name="tag"></param>
		protected internal LevelCollection(Tag tag)
		{
			m_array = null;
		}
		#endregion
		
		#region Operations (type-safe ICollection)

		/// <summary>
		/// Gets the number of elements actually contained in the <c>LevelCollection</c>.
		/// </summary>
		public virtual int Count
		{
			get { return m_count; }
		}

		/// <summary>
		/// Copies the entire <c>LevelCollection</c> to a one-dimensional
		/// <see cref="Level"/> array.
		/// </summary>
		/// <param name="array">The one-dimensional <see cref="Level"/> array to copy to.</param>
		public virtual void CopyTo(Level[] array)
		{
			this.CopyTo(array, 0);
		}

		/// <summary>
		/// Copies the entire <c>LevelCollection</c> to a one-dimensional
		/// <see cref="Level"/> array, starting at the specified index of the target array.
		/// </summary>
		/// <param name="array">The one-dimensional <see cref="Level"/> array to copy to.</param>
		/// <param name="start">The zero-based index in <paramref name="array"/> at which copying begins.</param>
		public virtual void CopyTo(Level[] array, int start)
		{
			if (m_count > array.GetUpperBound(0) + 1 - start)
			{
				throw new System.ArgumentException("Destination array was not long enough.");
			}
			
			Array.Copy(m_array, 0, array, start, m_count); 
		}

		/// <summary>
		/// Gets a value indicating whether access to the collection is synchronized (thread-safe).
		/// </summary>
		/// <value>true if access to the ICollection is synchronized (thread-safe); otherwise, false.</value>
		public virtual bool IsSynchronized
		{
			get { return m_array.IsSynchronized; }
		}

		/// <summary>
		/// Gets an object that can be used to synchronize access to the collection.
		/// </summary>
		public virtual object SyncRoot
		{
			get { return m_array.SyncRoot; }
		}

		#endregion
		
		#region Operations (type-safe IList)

		/// <summary>
		/// Gets or sets the <see cref="Level"/> at the specified index.
		/// </summary>
		/// <param name="index">The zero-based index of the element to get or set.</param>
		/// <exception cref="ArgumentOutOfRangeException">
		/// <para><paramref name="index"/> is less than zero</para>
		/// <para>-or-</para>
		/// <para><paramref name="index"/> is equal to or greater than <see cref="LevelCollection.Count"/>.</para>
		/// </exception>
		public virtual Level this[int index]
		{
			get
			{
				ValidateIndex(index); // throws
				return m_array[index]; 
			}
			set
			{
				ValidateIndex(index); // throws
				++m_version; 
				m_array[index] = value; 
			}
		}

		/// <summary>
		/// Adds a <see cref="Level"/> to the end of the <c>LevelCollection</c>.
		/// </summary>
		/// <param name="item">The <see cref="Level"/> to be added to the end of the <c>LevelCollection</c>.</param>
		/// <returns>The index at which the value has been added.</returns>
		public virtual int Add(Level item)
		{
			if (m_count == m_array.Length)
			{
				EnsureCapacity(m_count + 1);
			}

			m_array[m_count] = item;
			m_version++;

			return m_count++;
		}
		
		/// <summary>
		/// Removes all elements from the <c>LevelCollection</c>.
		/// </summary>
		public virtual void Clear()
		{
			++m_version;
			m_array = new Level[DEFAULT_CAPACITY];
			m_count = 0;
		}
		
		/// <summary>
		/// Creates a shallow copy of the <see cref="LevelCollection"/>.
		/// </summary>
		/// <returns>A new <see cref="LevelCollection"/> with a shallow copy of the collection data.</returns>
		public virtual object Clone()
		{
			LevelCollection newCol = new LevelCollection(m_count);
			Array.Copy(m_array, 0, newCol.m_array, 0, m_count);
			newCol.m_count = m_count;
			newCol.m_version = m_version;

			return newCol;
		}

		/// <summary>
		/// Determines whether a given <see cref="Level"/> is in the <c>LevelCollection</c>.
		/// </summary>
		/// <param name="item">The <see cref="Level"/> to check for.</param>
		/// <returns><c>true</c> if <paramref name="item"/> is found in the <c>LevelCollection</c>; otherwise, <c>false</c>.</returns>
		public virtual bool Contains(Level item)
		{
			for (int i=0; i != m_count; ++i)
			{
				if (m_array[i].Equals(item))
				{
					return true;
				}
			}
			return false;
		}

		/// <summary>
		/// Returns the zero-based index of the first occurrence of a <see cref="Level"/>
		/// in the <c>LevelCollection</c>.
		/// </summary>
		/// <param name="item">The <see cref="Level"/> to locate in the <c>LevelCollection</c>.</param>
		/// <returns>
		/// The zero-based index of the first occurrence of <paramref name="item"/> 
		/// in the entire <c>LevelCollection</c>, if found; otherwise, -1.
		///	</returns>
		public virtual int IndexOf(Level item)
		{
			for (int i=0; i != m_count; ++i)
			{
				if (m_array[i].Equals(item))
				{
					return i;
				}
			}
			return -1;
		}

		/// <summary>
		/// Inserts an element into the <c>LevelCollection</c> at the specified index.
		/// </summary>
		/// <param name="index">The zero-based index at which <paramref name="item"/> should be inserted.</param>
		/// <param name="item">The <see cref="Level"/> to insert.</param>
		/// <exception cref="ArgumentOutOfRangeException">
		/// <para><paramref name="index"/> is less than zero</para>
		/// <para>-or-</para>
		/// <para><paramref name="index"/> is equal to or greater than <see cref="LevelCollection.Count"/>.</para>
		/// </exception>
		public virtual void Insert(int index, Level item)
		{
			ValidateIndex(index, true); // throws
			
			if (m_count == m_array.Length)
			{
				EnsureCapacity(m_count + 1);
			}

			if (index < m_count)
			{
				Array.Copy(m_array, index, m_array, index + 1, m_count - index);
			}

			m_array[index] = item;
			m_count++;
			m_version++;
		}

		/// <summary>
		/// Removes the first occurrence of a specific <see cref="Level"/> from the <c>LevelCollection</c>.
		/// </summary>
		/// <param name="item">The <see cref="Level"/> to remove from the <c>LevelCollection</c>.</param>
		/// <exception cref="ArgumentException">
		/// The specified <see cref="Level"/> was not found in the <c>LevelCollection</c>.
		/// </exception>
		public virtual void Remove(Level item)
		{		   
			int i = IndexOf(item);
			if (i < 0)
			{
				throw new System.ArgumentException("Cannot remove the specified item because it was not found in the specified Collection.");
			}
			
			++m_version;
			RemoveAt(i);
		}

		/// <summary>
		/// Removes the element at the specified index of the <c>LevelCollection</c>.
		/// </summary>
		/// <param name="index">The zero-based index of the element to remove.</param>
		/// <exception cref="ArgumentOutOfRangeException">
		/// <para><paramref name="index"/> is less than zero</para>
		/// <para>-or-</para>
		/// <para><paramref name="index"/> is equal to or greater than <see cref="LevelCollection.Count"/>.</para>
		/// </exception>
		public virtual void RemoveAt(int index)
		{
			ValidateIndex(index); // throws
			
			m_count--;

			if (index < m_count)
			{
				Array.Copy(m_array, index + 1, m_array, index, m_count - index);
			}
			
			// We can't set the deleted entry equal to null, because it might be a value type.
			// Instead, we'll create an empty single-element array of the right type and copy it 
			// over the entry we want to erase.
			Level[] temp = new Level[1];
			Array.Copy(temp, 0, m_array, m_count, 1);
			m_version++;
		}

		/// <summary>
		/// Gets a value indicating whether the collection has a fixed size.
		/// </summary>
		/// <value>true if the collection has a fixed size; otherwise, false. The default is false</value>
		public virtual bool IsFixedSize
		{
			get { return false; }
		}

		/// <summary>
		/// Gets a value indicating whether the IList is read-only.
		/// </summary>
		/// <value>true if the collection is read-only; otherwise, false. The default is false</value>
		public virtual bool IsReadOnly
		{
			get { return false; }
		}

		#endregion

		#region Operations (type-safe IEnumerable)
		
		/// <summary>
		/// Returns an enumerator that can iterate through the <c>LevelCollection</c>.
		/// </summary>