Advanced Interactive Programming Componentbased Programming

1
Advanced Interactive ProgrammingComponent-based
Programming
2
Outline

• Component based programming
• Motivation
• Rationale
• ActiveX technologies
• COM/DCOM
• ActiveX components
• Create ActiveX controls in VB

3
Motivation

• The need for software reuse
• Speed up software development process
• Reduce software development cost
• Adapt to software (e.g. operating system) and
  hardware (e.g. microprocessor) changes
• The observation
• Many things in real world such as cars,
  computers, etc. are assembled from standard parts
• Similar development circumstances recur
  frequently in the development of computing systems

4
Reuse and Reuse Levels

• Reuse is a very broad term covering the general
  concept of a reusable asset.
• Reuse could happen at different steps of software
  engineering
• Requirements URD
• System specification - SRD
• System Design - ADD
• Reuse could happen at different levels of system
  abstraction
• Software source code - copypaste or OOP
• Software binary code

5
Understanding Component

• An executable binary piece of code, which has the
  following features
• Non-context-specific, i.e., functionally
  self-contained and independent of any specific
  environment or applications
• Composable with other components, i.e., used as a
  unit of third party composition, thus support
  multiple use
• A unit of independent deployment and versioning
• Encapsulated, i.e., a component needs to
  encapsulate its implementation and interact with
  its environment through well-defined interfaces

6
Component-based Programming

• Component-based programming is also known as
  component software development, which refers to
• Buy components from third parties
• Develop own components
• From scratch use what you learn such as OOP
• Or composition of other components
• Or a combination of the above two approaches
• Reusing and assembling components into
  applications
• Systems composed of software components are
  called component-based software or componentware

7
Object oriented programming Vs. Component-based
Programming

• Reuse of source code via object-oriented
  programming
• Reuse of an application binary code via
  component-based programming
• OOP is a way to build object-based software
  components
• Component-based programming is concerned with
  making objects (components) work together. The
  components may be created by many different tools

8
Benefits of Component Reuse

• Effective use of specialists
• Increased reliability
• Accelerated development (Rapid Application
  Development (RAD))
• Standards compliance
• Reduced risks

9
Costs of Component Reuse

• Thorough testing
• Fully documentation
• Robust input validity checking
• Pass back useful error messages as appropriate
• Maintaining a component library
• lost in flexibility and competitive edge
• Not-invented-here syndrome

10
Interoperability Problem and Solution

• Different individuals develop components in their
  own way
• How disparate components communicate with each
  other
• We need commonly agreed mechanisms for
  interaction between components
• Specifications, protocols and standards

11
Existing Component Technologies

• Java Beans (Enterprise Java Beans) - Sun
  MicroSystem, written in Java
• ActiveX and COM/DCOM - Microsoft for Windows
  platform
• CORBA (Common Object Request Broker Architecture
  (CORBA)) - Industry consortium known as the OMG,
  or Object Management Group

12
Understanding Component Revisited

• A component is an object written to a
  specification
• Which specification is not important
• Which language or on which platforms it is
  written is not important
• An object becomes a component as long as it
  adheres to a specification

13
Microsoft Component Technologies
14
ActiveX Technologies

• ActiveX is a framework that allows software
  components to co-operate even if they have been
  written by different vendors, at different times
  using different tools and different languages, no
  matter if the components are located in the same
  process, same machine or distributed over
  multiple machines on the Internet. Put simply,
  ActiveX provides the software plumbing between
  software objects and insulates the component
  developer from such complexities
• ActiveX contains a set of technologies that are
  applicable for standalone applications and the
  Internet
• ActiveX builds upon COM/DCOM

15
ActiveX Components

• ActiveX technologies define the interfaces for
  three types of component, each of them implements
  the particular ActiveX technology
• ActiveX controls (formerly OLE controls) (.ocx)
• Visible component that can be dropped into an
  application at design time, esp. for GUI design
• Code Components (.dll or .exe)
• Usually invisible components (can contain GUI)
  that provide a service
• ActiveX Documents (.dob)
• Visible components (similar to forms) that
  appears within Internet browser windows

16
Component Object Model (COM)

• The fundamental object model, or say
  specification describing how objects communicate
  with each other and also an objects life cycle
• The core of COM are these concepts
• Interfaces the mechanism through which an
  object exposes its functionality
• Reference counting the technique by which an
  object decides when it is no longer being used
  and is therefore free to remove itself
• QueryInterface the method used to query an
  object for a given interface
• Marshaling the mechanism that enables objects
  to be used across thread, process and network
  boundaries, allowing for location independence.
• Aggregation a way in which one object can make
  use of another.

17
Component Object Model (COM)

• Foundation for reusable component development,
  which also provide APIs
• Language, location, compiler and platform
  independent. Users of a component need not to
  know them
• Several ways to package or reuse COM objects
• .OCX, .DLLs, .EXE
• COM objects can contain both data and methods,
  and can only be accessed by a public interface.
  Familiar?

18
Distributed COM (DCOM)

• DCOM is an extension of the COM concepts and
  services to distributed systems
• DCOM extends component applications across the
  Internet, so COM components can be executed on
  remote machines
• DCOM is an open technology that runs on multiple
  platforms
• Other features such as security and transparency
  - hiding the implementation details such as
  connecting to remote machines

19
Classes or Components?

• Software components hide implementation, conform
  to interfaces, and encapsulate data, just like
  classes do in object-oriented languages.
• So how do components differ from classes? Almost
  all software components are also classes. What
  makes them components is their conformance to a
  software component specification.
• The COM Specification is the document that
  describes what a Microsoft class must do to be
  considered a component.

20
Creating ActiveX Controls in VB
21
ActiveX Controls

• An extension to the Visual Basic Toolbox
• A means for you to create your own controls
• Replace VBX controls (Visual Basic extension
  controls) used in VB 4 or earlier releases
• Build on OLE (Object Linking and Embedding)
  technology, which allows applications to work
  together seamlessly, e.g. using Excel spreadsheet
  within Word, also refers to as automation

22
ActiveX Control Types

• User-drawn controls
• Custom control developed from scratch
• The most difficult type but with the most design
  flexibility
• Enhanced controls
• Adding extra features to existing controls
• Aggregate controls
• Combining one or more existing controls to form a
  new one
• The most common control type

23
ActiveX Control Design

• Designing an ActiveX control is as easy as
  designing a form, and can be further customised
  using property pages, name constraints and events
• Beware that you are developing a component (a
  module) rather than an application common and
  reusable
• Provide functions rather than provide solution to
  an application business
• ActiveX controls can be compiled directly into
  .ocx files that can be used/reused with
  development tools

24
ActiveX Control Example

• Create an aggregate ActiveX control called
  LabelScrollbar
• It consists of two constituent controls, Label
  and Scrollbar
• Functions
• Allow a user to scroll a range of values
• The scrollbar value is displayed as the label
  caption
• Beware that LabelScrollbar is a single control

25
ActiveX Control Design

• Create (Open) an ActiveX control project

26
An Open ActiveX Control Project

• Similar to creating a Standard EXEs GUI using
  standard controls
• ActiveX control GUI not based on Form but on
  UserControl object

UserControl1
27
UserControl Object

• Is a container, like a form, where other controls
  can be sited
• Has sizing handler, properties and a folder in
  the project explorer
• Customizing a UserControl is like customizing a
  form
• Differences from a form
• Cannot run the UserControl directly to view its
  GUI
• Must put the ActiveX control in a container such
  as a form

28
UserControl Object Behaviour

• A UserControl behaves programmatically different
  from a form
• No Activate, Load, UnLoad, QueryUnload events
• Initialize and Terminate are similar
• Has InitProperties, ReadProperties,
  WriteProperties, Resize events
• Saved as .ctl file

29
UserControl Object Methods

• InitProperties initialize a controls
  properties every time a new instance is created
  in a container, only once in a controls lifetime
• ReadProperties set a controls properties if it
  not a new instance
• WriteProperties persist a controls property
  value when the design time instance destroyed
  when used in an application
• Resize specify how the constituent controls
  should size themselves when the control is resized

30
GUI Design - LabelScrollbar

• Design the controls GUI
• Configure properties

31
Programming Behaviour

• Each constituent control has properties, events
  and methods
• The UserControl object has properties, events and
  methods
• By default, properties, events and methods of
  constituent controls are hidden within the
  UserControl object

32
Programming Behaviour

• ActiveX control developers need to decide
• The interface of the ActiveX control
• Which properties or events or methods from which
  constituent control you want to expose
• Which properties or events or methods from the
  UserControl object you want to expose
• Any custom properties, events and methods
• The implementation within the ActiveX control
• The initialization, data persistence and
  termination

33
LabelScrollbar Behaviour

• One event Change
• Five properties, MAX, Min, LargeChange,
  SmallChange, Value
• All are mapped to the corresponding event and
  properties in the Horizontal Scrollbar
• Property initialization, setting, persistence and
  resizing behaviour
• No custom properties or events but could add one,
  e.g. the space between label and the scrollbar

34
LabelScrollbar Code

• Any events or properties the control will expose
  are placed in general declaration
• Events or properties in general declaration must
  be public

Developers using this control will see and be
able to code this event
35
Code Examples
36
Code Example (cont.)

• Notify the UserControls container of the change
• Properties window updated
• Raise the WriteProperties event

37
Raising Events in ActiveX Control

• Constituent controls events are hidden within
  the UserControl by default
• To expose them, must declare them as Event in
  general declaration
• Must be coded to raise (i.e. fire) the event

38
Testing an ActiveX Control

• Create a form as the container of the control in
  the same project
• Run the form application to test the
  functionality of the control
• UserControl object must be closed while testing

39
GUI Display
Form
ActiveX control Icon
40
Publishing the Control

• Once passed the testing, a .OCX file can be
  produced for the control for distribution
• VB provides tools for the generation of .OCX file
• Need to remove the testing form
• More ActiveXcontrols can be created and compiled
  into one .OCX file

41
Any Questions?
42
ActiveX Control Interface Wizard
43
Wizard Introduction
44
Selecting Interface Members

• Select interface members events, properties and
  methods from the aggregation of all events,
  properties and methods of all constituent controls

45
LabelScrollbar Interface Members
46
Creating Own Interface Members
47
Mapping ActiveX Controls Interface Members to
Constituent Controls Interface members
48
Summary very useful
49
Code Skeleton Generated by the Wizard
50
Customize Code

• Wizard only helps but cannot do all for you
• Add necessary procedures and modifications
• For LabelScrollbar example
• Add Resize and InitProperties procedures,
• Add code to the change event
• Modify the default values for ReadProperties and
  WriteProperties procedures

51
Ambient Object

• Provide the UserControl information about its
  container such as the Form
• When an Ambient property of a container changes,
  AmbientChanged event is raised
• UserControl_AmbientChanged event handler is
  called to handle this event
• The handler receives a string containing the
  changed propertys name

52
Extender Object

• Provide access to events, properties and methods
  controlled by the container your control is
  placed on
• For the UserControl object and developers who use
  the ActiveX control

53
Property Pages

• Allow the author of ActiveX control to group
  related properties conveniently rather than all
  in one property window
• Allow users to view and set these properties
• Optional for ActiveX controls, only for easy of
  use and convenience

54
Add Property Pages
55
Introduction
56
Properties Page Design
57
Grouping Properties Accordingly
58
Summary Report
59
Using Property Pages
60
Summary

• Component based programming
• Motivation
• Rationale
• ActiveX technologies
• COM/DCOM
• ActiveX components
• Create ActiveX controls in VB