{"id":453,"date":"2022-01-09T14:50:47","date_gmt":"2022-01-09T07:50:47","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=453"},"modified":"2022-06-03T15:06:06","modified_gmt":"2022-06-03T08:06:06","slug":"csharp-extend-interface","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-extend-interface\/","title":{"rendered":"C# Extend Interface"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to define an interface that extends a single interface or multiple interfaces.<\/p>\n\n\n\n

Extending an interface<\/h2>\n\n\n\n

C# allows an interface to extend one or more interfaces. The following example illustrates how to define an interface that extends another interface:<\/p>\n\n\n\n

First, define the IUndoable<\/code> interface that has one method Undo()<\/code>:<\/p>\n\n\n

interface<\/span> IUndoable<\/span>\n{\n    void<\/span> Undo<\/span>(<\/span>)<\/span>;\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, define the IRedoable<\/code> interface that extends the IUndoable<\/code> interface:<\/p>\n\n\n
interface<\/span> IRedoable<\/span> : IUndoable<\/span>\n{\n    void<\/span> Redo<\/span>(<\/span>)<\/span>;\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the IRedoable<\/code> interface inherits all the members of the IUndoable<\/code> interface. In other words, a class<\/a> that implements the IRedoable<\/code> interface must also provide implementations for Redo()<\/code> method in the IRedoable<\/code> interface and the Undo()<\/code> method of the IUndoable<\/code> interface.<\/p>\n\n\n\n
Third, define the Input<\/code> class that implements the IRedoable<\/code> interface:<\/p>\n\n\n
class<\/span> Input<\/span> : IRedoable<\/span>\n{\n    public<\/span> void<\/span> Redo<\/span>(<\/span>)<\/span>\n    {\n        Console.WriteLine(\"Redo\"<\/span>);\n    }\n\n    public<\/span> void<\/span> Undo<\/span>(<\/span>)<\/span>\n    {\n        Console.WriteLine(\"Undo\"<\/span>);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Finally, create an instance of the Input<\/code> class and call the Undo()<\/code> and Redo()<\/code> methods:<\/p>\n\n\n
var<\/span> input = new<\/span> Input();\ninput.Undo();\ninput.Redo();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Undo\nRedo<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Extending multiple interfaces<\/h2>\n\n\n\n
To define an interface that extends two or more interfaces, you use the following syntax:<\/p>\n\n\n
interface<\/span> IMyInterface<\/span>: IMyInterface1<\/span>, IMyInterface2<\/span>, IMyInterface3<\/span>\n{\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this case, the MyInterface<\/code> inherits all members from all the interfaces, including IMyInterface1<\/code>, IMyInterface2<\/code>, and IMyInterface3<\/code>. <\/p>\n\n\n\n
In other words, a class that implements the MyInterface<\/code> needs provide implementations for all the members of those interfaces.<\/p>\n\n\n\n
The following example illustrates how to define an interface that extends multiple interfaces.<\/p>\n\n\n\n
First, define two interfaces IStore<\/code> and IRetrieve<\/code>:<\/p>\n\n\n
interface<\/span> IStore<\/span>\n{\n    void<\/span> Store<\/span>(string<\/span> data<\/span>)<\/span>;\n}\n\ninterface<\/span> IRetrieve<\/span>\n{\n    string<\/span>? Retrieve();\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, define an interface IMessage<\/code> that extends the IStore<\/code> and IRetrieve<\/code> interfaces:<\/p>\n\n\n
interface<\/span> IMessage<\/span> : IStore<\/span>, IRetrieve<\/span>\n{\n    void<\/span> Delete<\/span>(<\/span>)<\/span>;\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The IMessage<\/code> interface has its own method Delete()<\/code>. It also inherits methods from the IStore<\/code> and IRetrieve<\/code> interfaces. It means that a class that implements the IMessage<\/code> interface needs to implement all three methods.<\/p>\n\n\n\n
Third, define the Message<\/code> class that implements the IMessage<\/code> interface:<\/p>\n\n\n
class<\/span> Message<\/span> : IMessage<\/span>\n{\n    private<\/span> string<\/span>? data = null<\/span>;\n\n    public<\/span> void<\/span> Delete<\/span>(<\/span>)<\/span>\n    {\n        data = null<\/span>;\n    }\n\n    public<\/span> string<\/span>? Retrieve()\n    {\n        return<\/span> data;\n    }\n\n    public<\/span> void<\/span> Store<\/span>(string<\/span> message<\/span>)<\/span>\n    {\n        data = message;\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Finally, create an instance of the Message<\/code> class and call its methods:<\/p>\n\n\n
\/\/ Program.cs<\/span>\n\nMessage message = new<\/span>();\n\nmessage.Store(\"Hello\"<\/span>);\nConsole.WriteLine(message.Retrieve());\nmessage.Delete();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Hello<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
  • An interface can extend one or more interfaces.<\/li>
  • A class that implements an interface needs to provide implementations for all the members of the interface and the members that the interface inherits from other interfaces.<\/li><\/ul>\n
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