C#高手请进啊！关于foreach 的问题啊！

Question

大家好，下面是我的代码，红色部分是出错的地方．请大家帮我纠正一下，不胜感激！using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;namespace TestCollection
{
    class ForeachFunction
    {
        static void Main(string[] args)
        {
            Vector someVector = new Vector();
            foreach (double component in someVector)
            {
                Console.WriteLine("Component is " + component);
            }
        }
    }
    #region The rest of the part realize the function of "foreach".But some errors occured.
    struct Vector : IEnumerable
    {
        public double x, y, z;        public IEnumerator GetEnumerator()
        {
            return new VectorEnumerator(this);
        }        private class VectorEnumerator : IEnumerator
        {
            Vector theVector;
            int location;            public VectorEnumerator(Vector theVector)
            {
                this.theVector = theVector;
                location = -1;
            }            public bool MoveNext()
            {
                ++location;
                return (location > 2) ? false : true;
            }
            public object Current
            {
                get
                {
                    if (location < -1 || location > 2)
                    {
                        throw new InvalidOperationException("The enumerator is either before the first element or " + "after the last element of the Vector");
                    }
                    return theVector[(uint)location];
                }
            }
            public void Reset()
            {
                location = -1;
            }
        }
    }
    #endregion}

Answer 1

不好意思，没有变成红色！
是这一句      public object Current 
            { 
                get 
                { 
                    if (location  < -1  ¦ ¦ location  > 2) 
                    { 
                        throw new InvalidOperationException("The enumerator is either before the first element or " + "after the last element of the Vector"); 
                    } 
                    return theVector[(uint)location]; 
                } 
            }

Answer 2

ＬＺ什么错误提示？
加个else看看 
get 
                { 
                    if (location  < -1  ¦ ¦ location  > 2) 
                    { 
                        throw new InvalidOperationException("The enumerator is either before the first element or " + "after the last element of the Vector"); 
                    } 
                    else
                    return theVector[(uint)location]; 
                } 

Answer 3

加了else了，还是一样的！
错误提示是：无法将带[]的索引应用于＂TestCollection.Vector＂类型的表达式!

Answer 4

Vector 还要继承一下IList接口，同时
                    return theVector[(uint)location];  
的uint也有问题，迭代器只接受int

Answer 5

晕啊，如果要继承IList接口，那么还要实现这个接口中的那么多方法啊！我这个程序也就是模仿一下foreach的内部功能！那么按照你的思路，你能给我一个完整的代码吗？

Answer 6

网络上很多，你搜一下IList就有无数的结果

Answer 7

楼主   把
 public object Current 
            { 
                get 
                { 
                    if (location  < -1  ¦ ¦ location  > 2) 
                    { 
                        throw new InvalidOperationException("The enumerator is either before the first element or " + "after the last element of the Vector"); 
                    } 
                    return theVector[(uint)location]; 
                } 
            } 
            public void Reset() 
            { 
                location = -1; 
            } 
        } 这部分，换成一个索引器，试试

Answer 8

错误应该是你的程序中使用的“2”不正确，因为它有可能大于theVector的个数。你试一试这样写：
private class VectorEnumerator : IEnumerator
        {
            Vector theVector;
            int location;
            readonly int count;            public VectorEnumerator(Vector theVector)
            {
                this.theVector = theVector;
                location = -1;
                count = theVector.Count;
            }            public bool MoveNext()
            {
                ++location;
                return (location  > count-1) ? false : true;
            }
            public object Current
            {
                get
                {
                    if (location  < -1  ¦ ¦ location  > count-1)
                    {
                        throw new InvalidOperationException("The enumerator is either before the first element or " + "after the last element of the Vector");
                    }
                    return theVector[(uint)location];
                }
            }
            public void Reset()
            {
                location = -1;
            }
        } 

Answer 9

//需实现一个取索引值的方法
struct Vector : IEnumerable
{
//....
    public object this[uint index]
    {
        get
        {
            return xxx;
        }
    }
//....
}

Answer 10

Current部分这么写 public object Current 
            { 
                get 
                { 
                    if (location  < -1  || location  > 2) 
                    { 
                        throw new InvalidOperationException("The enumerator is either before the first element or " + "after the last element of the Vector"); 
                    }
                    else if (location == 0)
                    {
                        return theVector.x;
                    }
                    else if (location == 1)
                    {
                        return theVector.y;
                    }
                    else
                    {
                        return theVector.z;
                    }
                } 
            } 
建议LZ多思考下。
本来没索引的，用所以一定出错。

Answer 11

可以用yield简化代码
using System; 
using System.Collections.Generic; 
using System.Text; 
using System.Collections; namespace TestCollection 
{ 
    class ForeachFunction 
    { 
        static void Main(string[] args) 
        { 
            Vector someVector = new Vector(); 
            foreach (double component in someVector) 
            { 
                Console.WriteLine("Component is " + component); 
            } 
        } 
    }     struct Vector : IEnumerable 
    { 
        public double x, y, z;         public IEnumerator GetEnumerator() 
        {
            yield return x;
            yield return y;
            yield return z;
        }         
    } }

Answer 12

http://hi.baidu.com/youniao/blog/item/d3448d2fbe0e4a3b1f308922.html

Answer 13

楼主,这是我改过后的代码，不知道是不是你想要的 ：using System;using System.Text;
using System.Collections;namespace TestCollection
{
    class ForeachFunction
    {
        static void Main(string[] args)
        {
            Vector someVector = new Vector(1,2,3);
            foreach (double component in someVector)
            {
                Console.WriteLine("Component is " + component);
            }
        }
    }
    #region The rest of the part realize the function of "foreach".But some errors occured.
    public struct Vector : IEnumerable
    {
        private double[] dd;
        //public double x, y, z;        public IEnumerator GetEnumerator()
        {
            return new VectorEnumerator(this);
        }
        public Vector(double x,double y,double z)
        {            dd = new double[3];
            dd[0] = x;
            dd[1] = y;
            dd[2] = z;
        }        private class VectorEnumerator : IEnumerator
        {
            Vector theVector;
            int location;            public VectorEnumerator(Vector theVector)
            {
                this.theVector = theVector;
                location = -1;
            }            public bool MoveNext()
            {
                ++location;
                return (location > 2) ? false : true;
            }
            public object Current
            {
                get
                {
                    if (location < -1 || location > 2)
                    {
                        throw new InvalidOperationException("The enumerator is either before the first element or " + "after the last element of the Vector");
                    }
                    return theVector.dd[(uint)location];                 }
            }
            public void Reset()
            {
                location = -1;
            }
        }
    }
    #endregion}