1Chapter :CCCCCCCC CCCCCCC CCCCCCC

By Noppadon Kamolvilassatian Dept. of Computer Engineering, Prin

ce of Songkla University Source: Mastering Visual Basic 5, Mi

crosoft Corporation

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• Animation• Explain the major constructs of COM.• Explain the major constructs of Automation.• Create a client application that can man

ipulate other applications through Auto mation, use multiple interfaces on an ob

ject, and receive notifications from a server.

Outline

• The Component Object Model (COM)• Implementing Automation• Characteristics of Server Components• Creating a Client in Visual Basic• Creating a Client that Uses Microsoft Excel

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• Overview of COM• Advantages of Using COM• The COM Specification• Using Interfaces• The IUnknown Interface• Client and Server Communication

Overview of COM

• Component: A unit of executable code that provides functionality.

COM specifies how components are created and how client applications connect to com

ponents.• Object: A combination of code and data tha

t can be treated as a unit.• Automation: Part of the COM specification

that defines a standard method for creating components and using objects.

Advantages of Using COM• - Binary Compatibility and Cross Platform DevelopmentCOM is independent of the development language and operating system.

• Code ReusabilityComponent technology enables reuse of objects in a variety of applications without knowledge about the implementations of objects.

• Version ControlNew functionality can be added to a component (by adding or changing the implementation of an interface) without affecting clients that already use the component.

The COM Specification

The COM specification defines:– How an object is created from a component.– How a client accesses features of the object.– The object's responsibility for destroying itself whe

n it is no longer in use.

All of these activities are handled by interf aces, which make using a server much e asier than before.

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Interfaces are groups of functions that pro vide connection points.

• Interfaces provide standardized access t o the methods and properties (functiona

lity).• They are a contract that ensures consist

ent access to functionality.• They structure that access so that serve

rs are easier to use.

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CCCCC CCCCCCCCCC A credit card object with two interfaces, IRetail and IManager , that provide functionality to

a retail store client and a credit manager client.

The IUnknown Interface

• The COM specification requires the follo wing functionality of all objects.

– The object must be able to keep track of the number of connections made to it. When no l

onger in use, it must be able to destroy itself.– The object must be capable of being queried

by a client for additional interfaces that it m ay support.

• In order to provide this functionality, all - objects have a built in interface named I

Unknown .

Funct i ons of t he I Unknown Int er f ace• The IUnknown interface has three func

tions.• The functions AddRef and Release kee

p track of the creation and destruction o f the object

• QueryInterface lets clients query for ot her interfaces provided by the object.

Client and Server Communication• COM supports three types of objects: -inprocess (DLL), - -out of process (EXE in se

parate process), and remote (DLL or EX E on a different machine via Distributed

COM or DCOM)• You use the exact same code to hook up

- - - to an in process, out of process, or remo te object.

Client and Server Communication• A client and an -in process server share t

he same address space.• A client and an - -out of process server has

to communicate across the process boundary.• The communication between a client an

d a remote server is even more complex.

COM and the Registry

• For a component to become available fo r clients, it must register itself with the

operating system. It updates a section in the system registry.

• At run time, the client (in conjunction wi th COM) uses the information in the regi

stry to call the server component.• Animation

Implementing Automation

• Automation is a technology for manipulating objects that are defined by an application or library from outside the application.

• Automation is the part of COM that enables objects to be created and programmed by cli

ents in a standard way.• Automation works through a standard interf

ace known as IDispatch . This interface expor ts any number of properties and methods su

pported by an object.

Type Libraries• Clients get information about Automation objects fro

m a server by inspecting the server component's type library. Also known as an object library.

– Interfaces supported by the object.

– The properties, methods, and events provided by the object.

– The return types and parameters types of the object's methods and events.

– The Dispatch IDs these methods and properties use.

– The name of the Help file and Help topics.

The Object Browser

• An Object Browser is a tool that lets you view the methods and properties of an A

utomation object.

• Demonstration

Object Models

• When a server is designed, the objects t hat it offers can be structured into an ob ject model.

• An object model organizes the objects in the server into a hierarchy that represe nts which objects contain other objects.

• This structure makes the server easier t o use.

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The IDispatch Interface

• The dispatch interface, IDispatch , is a st andard Automation interface designed f

or exposing component methods and pr operties to a client.

• This interface contains four functions.• The functions GetTypeInfoCount and GetTypeInfo obtain information about the i

nterfaces, methods, and properties that a component supports.

The IDispatch Interface

• GetIDsOfNames takes one or more prop erties and/or methods, and returns their

dispatch ID (dispID ) values as defined in the type library.

• Invoke takes a dispID and a pointer to a n array of parameters, and causes the o

bject to execute the associated property or method

Binding

• Animation on how late binding works

Characteristics of Server Component• Determining Where Server ComponentsRun• Notifying Clients

C CCCCC CCCCC C CCCC CCCCCC CC mponents Run

• -In process– - Implemented as a dynamic link library (DLL

).– Run in the same process space as its client application.– Most efficient communication

C CCCCC CCCCC C CCCC CCCCCC CC mponents Run

• - -Out of process– Implemented as an executable file.– Run in its own process space.– --Communication across process boundaries

- slower than an in process server.– - - A single instance of an out of process compo

nent can service many clients, share global dta, and insulate other client applications fr

om a client’s problem.

C CCCCC CCCCC C CCCC CCCCCC CC mponents Run

• Remote– - - Out of process components, located on a sep

arate machine.– --Communication overhead is very high slowest.– Allow processing on a more powerful computer.– The component can also be located closer to

the work it is doing (such as located closer t o a remote database).

CCCCCCCCC CCCCCCC• I f you wanted the component to perform a task tha

t you knew will need several minutes to complete, you would notify the client asynchronously when t

he server completed some task. Use events or callb acks to notify.

Creating a Client in Visual Basic

1. Set a reference to the type library of a component.

2 . Declare an object variable. 3. Create an object. 4. Use the object’s methods and properties.

Setting References

1. On the Project menu, click References.

2. In the References dialog box, select the

type library you want to connect to, and then click OK.

Declaring Object Variables

• Generic Object VariablesDim x As Object

• Specific Object VariablesDim ex as Excel.Application

• Specific variable declarations give bette r performance, and enable Visual Basic t o display data about the available metho

ds and properties.

Creating Objects

• Using the CreateObject FunctionDim objMyObject as Project1.Class1Set objMyObject = CreateObject("Project1.Class1")

• Using the New Keyword with a Set statementDim objMyObject as Project1.Class1Set objMyObject = New Project1.Class1

• The second method is more efficient in so me cases.

Using Automation Objects

• To invoke the methods and properties of the object you have created, use the dot

(.) operator.

object.[method]

Receiving Notification from S erver: Events

• When building a client, you need the kn ow which events are generated by the c

omponent, and implement each event wi th an event handler

Receiving Notification from Ser ver: Events

• First, declaring the event interfacePublic WithEvents obj as Server.Object

• Second, implement the event handlersPrivate Sub obj_Event1()' Take some action based on Event1.

End Sub

Private Sub obj_Event2(vNewValue As Variant)' Take some action based on Event2.

End Sub

Creating a Client that Uses Micro soft Excel

How to:• Use workbooks and charts.• Use Automation to create an instance of

Microsoft Excel, and then manipulate so me of its object’s methods and properties.

• Get and set property values to create and manipulate a chart object.

Demonstration

The Microsoft Excel Object MoCCC

The Microsoft Excel Object MoCCC• Use the dot (.) operator to reference objects

xl.Workbooks("BOOK1.XLS").Worksheets("SHEET1").Range("A1").Value = 5

• Use the Parent property to reference an object that is one level higher.

xlwb.Parent 'refers to the Application object

The Microsoft Excel Object MoCCC• Create object variables to reference to objects t

hat you use repeatedly.Dim xl as Excel.ApplicationDim xlSheet as Excel.WorksheetSet xl = CreateObject("Excel.Application")Set xlSheet = xl.Workbooks("BOOK1.XLS").Worksheets("SHEET1")

xlSheet.Range("A1").Value = 5

• Set a reference to an object by name of by index.set xlwb = xl.Workbooks("MYBOOK.XLS")set xlwb = xl.Workbooks(1)

• Creating an Instance of Microsof t Excel• Set a reference to the MS Excel type library:

-- -- 50Project >References >Microsoft Excel . Object Li.

• Using the New KeywordDim xl as Excel.ApplicationDim xlchart as Excel.ChartDim xlsheet as Excedl.Worksheet

set xl = New Excel.Applicationset xlchart = New Excel.Chartset xlsheet = New Excel.Worksheet

• Close Microsoft Excelxl.Quit

Using Methods in MS Excel

• Add a new workbook to the Workbooks collection

xl.Workbooks.Add ()

• Open a specific workbookxl.Workbooks.Open "c:\book1.xls "

Using Methods in MS Excel

• Error handling when opening a workbookDim xl as Excel.ApplicationDim xlwb as Excel.WorkBookOn Error Resume Nextset xl = CreateObject("Excel.Application")set xlwb = xl.Workbooks.Open ("c:\book1.xls")If Err <> 0 ThenMsgbox "Unable to open workbook."Unload Me

End If

Using Methods in MS Excel

• Close the active workbookxl.ActiveWorkbook.Close SaveChanges := False

• Close the workbook Book1.xlsxl.Workbooks("BOOK1.XLS").Close SaveChanges :=False

Getting and Setting Values

set xlsheet = _ xlapp.Workbooks("Book1").Worksheets("Sheet1")xlsheet.Range("A1").Value = 5xlsheet.Range("myrange").Value = 10

Getting and Setting Values

set xl = CreateObject("Excel.Application")' Explicitly state the exact hierarchy.xl.Workbooks("x.xls").Worksheets("s").Range("A1")

.Value = 5

' Assume the current active workbook and worksheet.

xl.Range("A2").Value = 5

' Establish object variable to reference objects.Set wb = xl.Workbooks("source.xls")Set ws = wb.Worksheets("sheet1")Set rg = ws.Range("A1")rg.Value = 5

Using the Charts Collection

• Select a series of cells on a worksheet and crea te a chart

xlsheet.Range("A1:D4").Selectset xlc = xl.Charts.Add()xlc.Type = xl3DColumn

• Set a reference to an existing chart, then chan ge the type of chart

set xlc = xl.workbooks("bk1.xls").Charts("mycht")

xlc.Type = xl3DColumn

Using the Charts Collection

Sub cmdCreateChart_Click()Dim xl as Excel.Application

Dim xlc as Excel.Chart

Set xl = CreateObject("Excel.Application")

xl.Visible = True

xl.Workbooks.Add

xl.Range("A1").Value = 3

xl.Range("A2").Value = 2

xl.Range("A1:A2").Select

Set xlc = xl.Charts.Add()

xlc.Type = xl3DColumn

End Sub

Lab (Demonstration)

Exercise 1: Controlling Microsoft Excel

In this exercise, you will control Microso CCCCC CCCCC CCCCC CCCCCC.

2 2 22222222 2 222222 222222222222

In this exercise, you will create a client application that uses the functionality of

a version of the Credit Card component, which is created in later chapters.

Exercise 1: Controlling Micros oft Excel

• 3 4The cells C and C have been named “Grow” 222 “Inflation” , .

• 2222 2222 22222 , 16:16 “Net_Profit.”

Exercise 2: Creating a ClientApplication

The Credit Card component exposes two interfaces.

1. The default interface validates the purchase of an item with these properties and methods.Name TypeCardNumber PropertyExpireDate PropertyPurchaseAmount PropertyApprove Method

2. The IManage interface is used to change the credit limit of a client.

Name Type

CreditLimit Property

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Handed in by 17 August, 3:30 pm.

• A 3-page summary of “ActiveX Demystified”.

• Answers to self-check questions with explanations of your answers.

• Complete code of lab exercise 1 and 2 with explanations of statements in the code.