IEnumerable Practical Application

1. The collection wants to support the foreach traversal, need to return an iterator (IEnumerator), and foreach will automatically invoke the iterator's State Migration (MoveNext (), curent, Reset ())

#regionAssembly mscorlib.dll, v4.0.0.0//C:\Program Files (x86) \reference Assemblies\microsoft\framework\. Netframework\v4.5\mscorlib.dll#endregionusingSystem;usingSystem.Runtime.InteropServices;namespacesystem.collections{//Summary://Supports A simple iteration over a nongeneric collection.[ComVisible (true)] [Guid ("496b0abf-cdee-11d3-88e8-00902754c43a")]     Public InterfaceIEnumerator {ObjectCurrent {Get; } BOOLMoveNext (); voidReset (); }}

2.IEnumerable interface to customize the requirements of foreach

#regionAssembly mscorlib.dll, v4.0.0.0//C:\Program Files (x86) \reference Assemblies\microsoft\framework\. Netframework\v4.5\mscorlib.dll#endregionusingSystem.Runtime.InteropServices;namespacesystem.collections{//Summary://exposes the enumerator, which supports a simple iteration over a non-generic//collection.[ComVisible (true)] [Guid ("496b0abe-cdee-11d3-88e8-00902754c43a")]     Public InterfaceIEnumerable {[DispID (-4)] IEnumerator GetEnumerator (); }}

3. List-like lists are defined as follows:

    /// <summary>    ///List/// </summary>    classMylist:arraylist, ienumerable<Object>    {        //The iterator returns         Publicienumerator<Object>GetEnumerator () {return NewMylistenumerator ( This); }        /// <summary>        ///1. Since IEnumerable<T>inherit from IEnumerable, so you must implement its method///2. Because a method with the same name already exists, you need to display the implementation/// </summary>        /// <returns></returns>IEnumerator Ienumerable.getenumerator () {//return GetEnumerator ();//IEnumerator is the base class of ienumerator<t>            return NULL; }    }    /// <summary>    ///A custom iterator for a list/// </summary>    classmylistenumerator:ienumerator<Object>    {        Private intCurrent =-1; PrivateMyList _mylist;  Publicmylistenumerator (MyList MyList) {_mylist=MyList; Current= _mylist = =NULL|| _mylist. Count = =0? -1:0; }         Public BOOLMoveNext () { current++; return_mylist! =NULL&& _mylist. Count >Current ; }        Objectienumerator<Object>. Current {Get            {                if(_mylist! =NULL&& _mylist. Count > Current)return_mylist[current]; return NULL; }        }        //1. Since Ienumerable<out T> inherits from IEnumerable, its methods must be implemented//2. Because a method with the same name already exists, you need to display the implementation        ObjectIEnumerator.Current {Get             {                //if (_mylist! = null && _mylist. Count > Current) return _mylist[current];                 return NULL; }         }         Public voidReset () { current= _mylist = =NULL|| _mylist. Count = =0? -1:0; }        //Ienumerator<t> inherits the IDisposable, so the method needs to be implemented in order to clean up the state after the Traverse is completed.//This method is automatically called after the Foreach loop is complete         Public voidDispose () {}}

4.IEnumerator as an iterator, derived from the underlying programming language pointers;

An important feature of a reference type that differs from a value type is that it is used only when the real processing is performed ;

. NET in the yield keyword is very good support, the following examples illustrate:

       Static voidMain (string[] args) {            varList = Getstrings (5); foreach(varIteminchlist)            {Console.WriteLine (item); } list= Getstrings (Ten); foreach(varIteminchlist)            {Console.WriteLine (item);        } console.readline (); }
Operation Result:
        /// <summary>        ///1.yield return puts the results of a single operation into the IEnumerable collection///2.yield Break breaks the scope of the current iterator/// </summary>        /// <param name= "Length" ></param>        /// <returns></returns>         Public Staticienumerable<string> getstrings (intLength =0)        {             for(inti =0; i < length; i++)            {                if(I <5)                {                    yield return string. Format ("First {0} calls", i); }                Else                {                    yield  Break; }} Console.WriteLine ("code within the iteration scope after yield break is no longer executed"); }

Add: The above getstrings traditionally many people are accustomed to the following wording, but the time spent in doing so is n*m, where n is the length of the list to be calculated, and M is the first traversal length, which is why the above emphasis on the use of the time will be real processing

  Public Staticlist<string> getstrings (intLength =0)        {            varresult =Newlist<string>();  for(inti =0; i < length; i++)            {                if(I <5) {result. ADD (string. Format ("First {0} calls", i)); }            }            returnresult; }

IEnumerable Practical Application