C # Knowledge points-enumerators and iterators

I. Understanding of several basic concepts

Question one: Why arrays can use the foreach output elements

A: An array is an enumerable type that implements an enumerator (enumerator) object, the enumerator knows the order of the elements and tracks their positions, and then returns the current item of the request

Question two: Can I traverse the elements without foreach?

Question three: What is an enumerable class

A: An enumerable class is a class that implements the IEnumerable interface; The IEnumerable interface has only one member GetEnumerator method, which returns an enumerator for the object

Question four: What is an enumerator

A: The enumerator that implements the IEnumerator interface contains three function members: Current,movenext,reset

Current is a read-only property that returns a reference to type object;

MoveNext is the method of advancing the enumerator position to the next item of the collection, which returns a Boolean value indicating whether the new position is valid or has exceeded the tail of the sequence;

Reset is the method of resetting the position to its original state;

Second, the following code shows a complete example of an enumerable class

1 namespaceConsoleApplication42{3     // <summary>4     /// Customize an Enumeration object5     // </summary>6     classColorenumerator:ienumerator7{8         Private string[] _colors;9         Private int_position =-1;Ten  One          PublicColorenumerator (string[] arr) A{ -_colors = arr; -              for(inti = 0; I < arr. Length; i++) the{ -_colors[i] = Arr[i]; -} -} +          Public ObjectCurrent -{ +             Get A{ at                 if(_position = =-1) -{ -                     Throw NewInvalidOperationException (); -} -                 if(_position >= _colors. Length) -{ in                     Throw NewInvalidOperationException (); -} to                 return_colors[_position]; +} -} the  *          Public BOOLMoveNext () ${Panax Notoginseng             if(_position < _colors. LENGTH-1) -{ the_position++; +                 return true; A} the             Else +{ -                 return false; $} $} -  -          Public voidReset () the{ -_position =-1;Wuyi} the} -  Wu     // <summary> -     /// Create an enumeration class that implements the IEnumerable interface About     // </summary> $     classSpectrum:ienumerable -{ -         Private string[] Colors = {"Red", "Yellow", "Blue" }; -          PublicIEnumerator GetEnumerator () A{ +             return NewColorenumerator (Colors); the} -} $  the     classProgram the{ the         Static voidMain (string[] args) the{ -Spectrum Spectrum =NewSpectrum (); in             foreach(stringColorinchSpectrum the{ theConsole.WriteLine (color); About} theConsole.readkey (); the} the} +} - 

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C. Generic Enumeration interface

The GetEnumerator method of the Ienumerable<t> interface returns an instance of the enumeration class that implements the Ienumerator<t>;

The class implementing the Ienumerator<t> implements the current property, which returns objects of the actual type, not references to the object base class;

So implementations of non-generic interfaces are not type-safe, because they also need to be converted to actual types.

Iv. iterators 1. Using iterators to create enumerators

1 namespaceConsoleApplication52{3     classMyClass4{5         // <summary>6         /// get an iterator7         // </summary>8         // <returns></returns>9          Publicienumerator<string> GetEnumerator ()Ten{ One             returnColorenumerator (); A} -         // <summary> -         /// iterators the         // </summary> -         // <returns></returns> -          Publicienumerator<string> Colorenumerator () -{ +Yieldreturn"Red"; -Yieldreturn"Yellow"; +Yieldreturn"Blue"; A} at} -     classProgram -{ -         Static voidMain (string[] args) -{ -MyClass MC =NewMyClass (); in             foreach(stringColorinchMc -{ toConsole.WriteLine (color); +} -Console.readkey (); the} *} $}

View Code2. Using iterators to create enum types

1 namespaceConsoleApplication62{3     classMyClass4{5          Publicienumerator<string> GetEnumerator ()6{7             //Get enumerable types8ienumerable<string> enumerable = colorenumerable ();9             //Get enumeratorTen             returnColorenumerable (). GetEnumerator (); One} A  -          Publicienumerable<string> colorenumerable () -{ theYieldreturn"Red"; -Yieldreturn"Yellow"; -Yieldreturn"Blue"; -} +} -     classProgram +{ A         Static voidMain (string[] args) at{ -MyClass MC =NewMyClass (); -             //Use class object -             foreach(stringColorinchOck -{ -Console.WriteLine (color); in} -Console.WriteLine ("-----------------------"); to             //methods for using class enumerators +             foreach(stringColorinchMc. Colorenumerable ()) -{ theConsole.WriteLine (color); *} $Console.readkey ();Panax Notoginseng} -} the}

View Code3. Generate multiple iterative types

1 namespaceConsoleApplication72{3     classMyClass4{5         Private string[] Colors = {"Red", "Yellow", "Blue" };6         //Order7          Publicienumerable<string> Colororder ()8{9              for(inti = 0; i < colors.length; i++)Ten{ OneYieldreturnColors[i]; A} -} -         //Reverse Order the          Publicienumerable<string> colorreversed () -{ -              for(inti = colors.length-1; I >= 0; i--) -{ +YieldreturnColors[i]; -} +} A} at     classProgram -{ -         Static voidMain (string[] args) -{ -MyClass MC =NewMyClass (); -             foreach(stringColorinchMc. Colororder ()) in{ -Console.WriteLine (color); to} +Console.WriteLine ("------------------"); -             foreach(stringColorinchMc. Colorreversed ()) the{ *Console.WriteLine (color); $}Panax NotoginsengConsole.readkey (); -} the} +} A 

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C # Knowledge points-enumerators and iterators