Compilation of basic knowledge of C# Basic knowledge (17) ILiest interface - generics

Inserting a value type into ArrayList will trigger a boxing operation, and retrieving a value type requires unboxing, as follows

            ArrayList myArrayList = new ArrayList();

            myArrayList.Add(40);//装箱

            myArrayList.Add(80);//装箱
            
            Int32 a1 = (Int32)myArrayList[0];//拆箱

            Int32 a2 = (Int32)myArrayList[1];//拆箱

This will cause performance consumption. As for the detailed explanation of packing, see the next article.
In order to solve these problems, C# has the IList interface that supports generics. Let’s look at the detailed code below. In fact, the structure is the same as IList, except that generics are added.

 /// <summary>
    /// 泛型集合类
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class List<T> : IList<T>, IList
    {
        /// <summary>
        /// 泛型迭代器
        /// </summary>
        /// <typeparam name="T"></typeparam>
        public struct Enumertor<T> : IEnumerator, IEnumerator<T>
        {
            //迭代索引
            private int index;

            //迭代器所属的集合对象引用
            private List<T> list;

            public Enumertor(List<T> container)
            {
                this.list = container;

                this.index = -1;
            }

            public void Dispose()
            {
            }

           /// <summary>
           /// 显示实现IEnumerator的Current属性
           /// </summary>
            object IEnumerator.Current
            {
                get
                {
                    return list[index];
                }
            }

            /// <summary>
            /// 实现IEnumerator<T>的Current属性
            /// </summary>
            public T Current
            {
                get
                {
                    return list[index];
                }
            }

            /// <summary>
            /// 迭代器指示到下一个数据位置
            /// </summary>
            /// <returns></returns>
            public bool MoveNext()
            {
                if (this.index < list.Count)
                {
                    ++this.index;
                }

                return this.index < list.Count;
            }

            public void Reset()
            {
                this.index = -1;
            }
        }

        /// <summary>
        /// 保存数据的数组，T类型则体现了泛型的作用。
        /// </summary>
        private T[] array;

        /// <summary>
        /// 当前集合的长度
        /// </summary>
        private int count;

        /// <summary>
        /// 默认构造函数
        /// </summary>
        public List()
            : this(1)
        {

        }

        public List(int capacity)
        {
            if (capacity < 0)
            {
                throw new Exception("集合初始长度不能小于0");
            }

            if (capacity == 0)
            {
                capacity = 1;
            }

            this.array = new T[capacity];
        }

        /// <summary>
        /// 集合长度
        /// </summary>
        public int Count
        {
            get
            {
                return this.count;
            }
        }

        /// <summary>
        /// 集合实际长度
        /// </summary>
        public int Capacity
        {
            get
            {
                return this.array.Length;
            }
        }

        /// <summary>
        /// 是否固定大小
        /// </summary>
        public bool IsFixedSize
        {
            get
            {
                return false;
            }
        }

        /// <summary>
        /// 是否只读
        /// </summary>
        public bool IsReadOnly
        {
            get
            {
                return false;
            }
        }

        /// <summary>
        /// 是否可同属性
        /// </summary>
        public bool IsSynchronized
        {
            get
            {
                return false;
            }
        }

        /// <summary>
        /// 同步对象
        /// </summary>
        public object SyncRoot
        {
            get
            {
                return null;
            }
        }

        /// <summary>
        /// 长度不够时，重新分配长度足够的数组
        /// </summary>
        /// <returns></returns>
        private T[] GetNewArray()
        {
            return new T[(this.array.Length + 1) * 2];
        }

        /// <summary>
        /// 实现IList<T>Add方法
        /// </summary>
        /// <param name="value"></param>
        public void Add(T value)
        {
            int newCount = this.count + 1;

            if (this.array.Length < newCount)
            {
                T[] newArray = GetNewArray();

                Array.Copy(this.array, newArray, this.count);

                this.array = newArray;
            }

            this.array[this.count] = value;

            this.count = newCount;
        }

        /// <summary>
        /// 向集合末尾添加对象
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
         int IList.Add(object value)
        {
            ((IList<T>)this).Add((T)value);

            return this.count - 1;
        }

        /// <summary>
        /// 实现IList<T>索引器
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        public T this[int index]
        {
            get
            {
                if (index < 0 || index >= this.count)
                {
                    throw new ArgumentOutOfRangeException("index");
                }

                return this.array[index];
            }

            set
            {
                if (index < 0 || index >= this.count)
                {
                    throw new ArgumentOutOfRangeException("index");
                }

                this.array[index] = value;
            }
        }

        /// <summary>
        /// 显示实现IList接口的索引器
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        object IList.this[int index]
        {
            get
            {
                return ((IList<T>)this)[index];
            }

            set
            {
                ((IList<T>)this)[index] = (T)value;
            }
        }

        /// <summary>
        /// 删除集合中的元素
        /// </summary>
        /// <param name="index"></param>
        /// <param name="count"></param>
        public void RemoveRange(int index, int count)
        {
            if (index < 0)
            {
                throw new ArgumentOutOfRangeException("index");
            }

            int removeIndex = index + count;

            if (count < 0 || removeIndex > this.count)
            {
                throw new ArgumentOutOfRangeException("index");
            }

            Array.Copy(this.array, index + 1, this.array, index + count - 1, this.count - removeIndex);

            this.count -= count;
        }

        /// <summary>
        /// 实现IList<T>接口的indexOf方法
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public int IndexOf(T value)
        {
            int index = 0;

            if (value == null)
            {
                while (index < this.count)
                {
                    if (this.array[index] == null)
                    {
                        return index;
                    }

                    ++index;
                }
            }
            else
            {
                while (index < this.count)
                {
                    if (value.Equals(this.array[index]))
                    {
                        return index;
                    }

                    ++index;
                }
            }
            return -1;
        }

        /// <summary>
        /// 显示实现IList接口的IndexOf方法
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
         int IList.IndexOf(object value)
        {
            return ((IList<T>)this).IndexOf((T)value);
        }

        /// <summary>
        /// 查找对应数组项
        /// </summary>
        /// <param name="o"></param>
        /// <param name="compar"></param>
        /// <returns></returns>
        public int IndexOf(object o, IComparer compar)
        {
            int index = 0;

            while (index < this.count)
            {
                if (compar.Compare(this.array[index], o) == 0)
                {
                    return index;
                }

                ++index;
            }

            return -1;
        }

        /// <summary>
        /// 实现IList<T>接口的Remove方法
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public bool Remove(T value)
        {
            int index = this.IndexOf(value);

            if (index >= 0)
            {
                this.RemoveRange(index, 1);

                return true;
            }

            return false;
        }

        /// <summary>
        /// 显示实现IList接口的Remove方法，此处显示实现
        /// </summary>
        /// <param name="value"></param>
        void IList.Remove(object value)
        {
            ((IList<T>)this).Remove((T)value);
        }

        /// <summary>
        /// 从集合指定位置删除对象的引用
        /// </summary>
        /// <param name="index"></param>
        public void RemoveAt(int index)
        {
            RemoveRange(index, 1);
        }

        /// <summary>
        /// 弹出集合的最后一个元素
        /// </summary>
        /// <returns></returns>
        public object PopBack()
        {
            object o = this.array[this.count - 1];

            RemoveAt(this.count - 1);

            return o;
        }

        /// <summary>
        /// 弹出集合第一个对象
        /// </summary>
        /// <returns></returns>
        public object PopFront()
        {
            object o = this.array[0];

            RemoveAt(0);

            return o;
        }

        /// <summary>
        /// 实现IList<T>接口的Insert方法
        /// </summary>
        /// <param name="index"></param>
        /// <param name="value"></param>
        public void Insert(int index, T value)
        {
            if (index >= this.count)
            {
                throw new ArgumentOutOfRangeException("index");
            }

            int newCount = this.count + 1;

            if (this.array.Length < newCount)
            {
                T[] newArray = GetNewArray();

                Array.Copy(this.array, newArray, index);

                newArray[index] = value;

                Array.Copy(this.array, index, newArray, index + 1, this.count - index);

                this.array = newArray;
            }
            else
            {
                Array.Copy(this.array, index, this.array, index + 1, this.count - index);

                this.array[index] = value;
            }

            this.count = newCount;
        }

        /// <summary>
        /// 显示实现IList接口的Insert方法
        /// </summary>
        /// <param name="index"></param>
        /// <param name="value"></param>
        void IList.Insert(int index, object value)
        {
            ((IList<T>)this).Insert(index, (T)value);
        }

        /// <summary>
        /// 实现IList<T>接口的Contains方法
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public bool Contains(T value)
        {
            return this.IndexOf(value) >= 0;
        }

        /// <summary>
        /// 显示实现IList<T>接口的Contains方法
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        bool IList.Contains(object value)
        {
            return ((IList<T>)this).IndexOf((T)value) >= 0;
        }

        /// <summary>
        /// 将集合压缩为实际长度
        /// </summary>
        public void TrimToSize()
        {
            if (this.array.Length > this.count)
            {
                T[] newArray = null;

                if (this.count > 0)
                {
                    newArray = new T[this.count];

                    Array.Copy(this.array, newArray, this.count);
                }
                else
                {
                    newArray = new T[1];
                }

                this.array = newArray;
            }
        }

        /// <summary>
        /// 清空集合
        /// </summary>
        public void Clear()
        {
            this.count = 0;
        }

        /// <summary>
        /// 实现IEnumerable接口的GetEnumerator方法
        /// </summary>
        /// <returns></returns>
        public IEnumerator<T> GetEnumerator()
        {
            Enumertor<T> ator = new Enumertor<T>(this);

            return ator;
        }

        /// <summary>
        /// 显示实现IEnumerable接口的GetEnumerator方法
        /// </summary>
        /// <returns></returns>
        IEnumerator IEnumerable.GetEnumerator()
        {
            return ((IEnumerable<T>)this).GetEnumerator();
        }

        /// <summary>
        /// 实现ICollection<T>接口的CopyTo方法
        /// </summary>
        /// <param name="array"></param>
        /// <param name="index"></param>
        public void CopyTo(T[] array, int index)
        {
            Array.Copy(this.array, 0, array, index, this.count);
        }

        /// <summary>
        /// 显示实现实现ICollection<T>接口的CopyTo方法
        /// </summary>
        /// <param name="array"></param>
        /// <param name="index"></param>
        void ICollection.CopyTo(Array array, int index)
        {
            Array.Copy(this.array, 0, array, index, this.count);
        }
    }

Call:

 static void Main(string[] args)
        {
            //由于已经指定了int，因此加入值类型不会有装箱拆箱操作。
            List<int> tList = new List<int>();

            tList.Add(25);

            tList.Add(30);

            foreach (int n in tList)
            {
                Console.WriteLine(n);
            }

            Console.ReadLine();
        }

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