C#手写简单的的List

1、定义自己的IMyList接口

namespace DataStructure
{
    public interface IMyList<T>
    {
        T this[int index] {  get;  set; }
        void Add(T value);
        bool Contains(T value);
        void Clear();
        int IndexOf(T value);
        void Insert(int index, T value);
        bool Remove(T value);
        void RemoveAt(int index);
        int Count { get; }
    }
}

2、定义自己的MyList实现IMyList接口

using System;

namespace DataStructure
{
    public class MyList<T>:IMyList<T>
    {
        private readonly T[] _items;

        private readonly int _maxLength;
        
        public int Count { get; private set; }
        
        public T this[int index]
        {
            get => _items[index];
            set => _items[index] = value;
        }

        public MyList(int maxLength)
        {
            Count = 0;
            _items=new T[maxLength];
            _maxLength = maxLength;
        }

        public void Add(T value)
        {
            if (Count+1 > _maxLength)
            {
                throw new Exception("超过定义的最大长度了");
            }
            _items[Count] = value;
            Count++;
        }
        
        public bool Contains(T value)
        {
            for (var i = 0; i < Count; i++)
            {
                if (value .Equals(_items[i]))
                {
                    return true;
                }
            }
            return false;
        }

        public void Clear()
        {
            Count = 0;
        }

        public int IndexOf(T value)
        {
            for (var i = 0; i < Count; i++)
            {
                if (value .Equals(_items[i]))
                {
                    return i;
                }
            }
            return -1;
        }
        
        public void Insert(int index, T value)
        {
            if (Count+1 > _maxLength)
            {
                throw new Exception("超过定义的最大长度了");
            }

            if (index < 0)
            {
                throw new Exception("index不能为负数");
            }
            
            for (var i = Count-1; i >= index; i--)
            {
                _items[i + 1] = _items[i];

            }
            _items[index] = value;
            Count++;
        }

        //返回true说明List中包含了value值，返回false说明List中没有value值
        public bool Remove(T value)
        {
            var index=IndexOf(value);
            if (index <= -1) return false;
            RemoveAt(index);
            return true;
        }

        public void RemoveAt(int index)
        {
            if (index < 0)
            {
                throw new Exception("index不能为负数");
            }

            if (index >= Count)
            {
                throw new Exception("index超过了当前数组的最大角标了");
            }
            
            for (var i = index; i < Count; i++)
            {
                _items[i]= _items[i + 1];

            }
            Count--;
        }

        public override string ToString()
        {
            var str="";
            for (var i = 0; i < Count; i++)
            {
                str += _items[i].ToString()+" ";
            }
            return str;
        }
    }
}

注意：自己写的MyList的数组长度是固定的，那么程序集中的List是怎么实现可以增加任意个元素呢。查看List源码，来看看它的add方法是怎么实现的。注释部分实现内部数组动态扩展的核心部分。

        public void Add(T item)
        {
            //这里当长度等于内置数组的长度时，扩大数组长度。
            if (this._size == this._items.Length)
                this.EnsureCapacity(this._size + 1);
            this._items[this._size++] = item;
            ++this._version;
        }

        private void EnsureCapacity(int min)
        {
            if (this._items.Length >= min)
                return;
            //这里判断数组长度是否为0，为0就设置长度为4，不为0就是扩大数组长度为原来的两倍
            int num = this._items.Length == 0 ? 4 : this._items.Length * 2;
            if ((uint) num > 2146435071U)
                num = 2146435071;
            if (num < min)
                num = min;
            this.Capacity = num;
        }

        public int Capacity
        {
            [__DynamicallyInvokable] get
            {
                return this._items.Length;
            }
            [__DynamicallyInvokable] set
            {
                if (value < this._size)
                    ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.value, ExceptionResource.ArgumentOutOfRange_SmallCapacity);
                if (value == this._items.Length)
                    return;
                if (value > 0)
                {
                    T[] objArray = new T[value];
                    //这里将原来数组的数据复制到新的数组中。
                    if (this._size > 0)
                        Array.Copy((Array) this._items, 0, (Array) objArray, 0, this._size);
                    this._items = objArray;
                }
                else
                    this._items = List<T>._emptyArray;
            }
        }