8.9 Interfaces

王朝other·作者佚名  2006-01-10
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8.9 Interfaces

An interface defines a contract. A class or struct that implements an

interface must adhere to its contract.

Interfaces can contain methods, properties, events, and indexers as members.

The example

interface IExample

{

string this[int index] { get; set; }

event EventHandler E;

void F(int value);

string P { get; set; }

}

public delegate void EventHandler(object sender, EventArgs e);

shows an interface that contains an indexer, an event E, a method F, and a

property P.

Interfaces may employ multiple inheritance. In the example

interface IControl

{

void Paint();

}

Chapter 8 Language Overview

43

interface ITextBox: IControl

{

void SetText(string text);

}

interface IListBox: IControl

{

void SetItems(string[] items);

}

interface IComboBox: ITextBox, IListBox {}

the interface IComboBox inherits from both ITextBox and IListBox.

Classes and structs can implement multiple interfaces. In the example

interface IDataBound

{

void Bind(Binder b);

}

public class EditBox: Control, IControl, IDataBound

{

public void Paint() {.}

public void Bind(Binder b) {.}

}

the class EditBox derives from the class Control and implements both

IControl and IDataBound.

In the previous example, the Paint method from the IControl interface and

the Bind method from

IDataBound interface are implemented using public members on the EditBox

class. C# provides an

alternative way of implementing these methods that allows the implementing

class to avoid having these

members be public. Interface members can be implemented using a qualified

name. For example, the

EditBox class could instead be implemented by providing IControl.Paint and

IDataBound.Bind

methods.

public class EditBox: IControl, IDataBound

{

void IControl.Paint() {.}

void IDataBound.Bind(Binder b) {.}

}

Interface members implemented in this way are called explicit interface

members because each member

explicitly designates the interface member being implemented. Explicit

interface members can only be

called via the interface. For example, the EditBox.s implementation of the

Paint method can be called

only by casting to the IControl interface.

class Test

{

static void Main() {

EditBox editbox = new EditBox();

editbox.Paint(); // error: no such method

IControl control = editbox;

control.Paint(); // calls EditBox.s Paint implementation

}

}

 
 
 
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