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// The IDbConnection interface defines a common

// set of members supported by all connection objects.

public interface IDbConnection : IDisposable

{

// Methods

IDbTransaction BeginTransaction();

IDbTransaction BeginTransaction(IsolationLevel il);

void ChangeDatabase(string databaseName);

void Close();

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IDbCommand CreateCommand();

void Open();

// Properties

string ConnectionString { get; set;}

int ConnectionTimeout { get; }

string Database { get; }

ConnectionState State { get; }

}

■

Note

By convention, .NET interface types are prefixed with a capital letter “I.” When you are creating your own

custom interfaces, it is considered a best practice to do the same.

Don’t concern yourself with the details of what these members actually do at this point. Simply

understand that the IDbConnection interface defines a set of members that are common to all

ADO.NET connection objects. Given this, you are guaranteed that each and every connection object

supports members such as Open(), Close(), CreateCommand(), and so forth. Furthermore, given that

interface members are always abstract, each connection object is free to implement these methods

in its own unique manner.

Another example: the System.Windows.Forms namespace defines a class named Control, which

is a base class to a number of Windows Forms UI widgets (DataGridView, Label, StatusBar, TreeView,

etc.). The Control class implements an interface named IDropTarget, which defines basic drag-and-

drop functionality:

public interface IDropTarget

{

// Methods

void OnDragDrop(DragEventArgs e);

void OnDragEnter(DragEventArgs e);

void OnDragLeave(EventArgs e);

void OnDragOver(DragEventArgs e);

}

Based on this interface, we can now correctly assume that any class that extends System.

Windows.Forms.Control supports four subroutines named OnDragDrop(), OnDragEnter(),

OnDragLeave(), and OnDragOver().

As you work through the remainder of this text, you will be exposed to dozens of interfaces that

ship with the .NET base class libraries. As you will see, these interfaces can be implemented on your

own custom classes and structures to define types that integrate tightly within the framework.