Widget Toolkits and Component Technology

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Widget Toolkits andComponent Technology
Computer Science 160 Fall 1998
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Widget Toolkit Overview

• Widget Properties
• Affordance
• Grouping
• Widget Look and Feel

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Widget Properties

• Acquired / Released
• Enabled / Disabled
• Active / Inactive
• Echo

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Acquired / Released

• Only a few logical functions active at a time
• If a logical input has its resources allocated,
  then it is acquired
• Example - Menu systems

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Enabled / Disabled

• Input to widget does not make sense
• Examples
• Why not just remove the options?

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Active / Inactive

• Need to know if the widget is responding to user
  input (feedback).
• Examples

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Echo

• How the widget reflects its current state
• Examples

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Affordance

• What can be manipulated
• What happens when object is manipulated

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Grouping

• Can group widgets
• Proximity and visual similarity
• Should group related widgets
• Menus
• Palettes
• Button bars
• Why?

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Grouping (2)

• Visual Structure
• easier to find things
• Screen space
• Cannot display all controls at once
• Makes sense to group things for searching
• 7 /- 2 chunks

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Optimized for Screens

• Should require minimal screen space
• Still have visual feedback and functionality

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Look and Feel

• Ease of Learning
• what each widget is for and how to use it
• consistency is key

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Look and Feel (2)

• Ease of Use
• is it easy or difficult for users to manipulate?
• Consistency is key
• make buttons look like buttons
• make menus look like menus
• visual processing can discard irrelevant info

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Look and Feel (3)

• Attractive and Engaging
• looks good!
• but dont forget functionality

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Transition

• That is all for Widget Toolkits
• Time to move on to Component Technology

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Component Tech Overview

• Components?
• ActiveX
• JavaBeans
• CORBA

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Components?

• Reusability
• standard interfaces interchangeable parts
• Portable
• cross-platform usage
• Interoperability
• use with other components
• Fast and easy to use

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Component Examples

• Delphi
• Visual Basic
• JavaBeans
• OpenDoc (defunct)

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Whats the Big Deal?

• How are components different from class libraries
  or GUI widgets?
• Design-Time interfaces
• Builder tools can query components
• Determine properties of component
• Determine events component responds to
• Determine what methods it has
• No source code necessary!

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Whats the Big Deal? (2)

• Examples

Super Mojo
Visual Cafe
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Whats the Big Deal? (3)

• Domain experts rather than coders can use
  components
• Could this be the next Silver Bullet?
• Buy and use someone elses code easily
• Reduce development time
• Reduce bugs!

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ActiveX

• Microsofts approach to components
• Refers to the set of technologies and tools
• cross-platform
• language-independent
• networked environments
• Roughly equivalent to Java applets

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ActiveX (2)

• Based on Common Object Model (COM)
• Network based is called DCOM
• Every ActiveX control comes with identifiers that
  describe its interfaces (GUID)
• Can query an ActiveX control for supported
  interfaces
• Then call the method through standard library

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ActiveX (3)

• Advantages
• Works on Windows and Macintosh systems
• Can be created using several languages and tools

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JavaBeans

• Component model for Java
• A Bean is a reusable software component that can
  be visually manipulated in builder tools.
• AWT widgets are JavaBeans too

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JavaBeans (2)

• Difference between Bean and Class is
  Introspection
• look inside a bean to determine properties
• Uses well-defined patterns and conventions
• e.g. setX() and getX() accessor and modifier
• Can define own PropertyEditor

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JavaBeans (3)

• Advantages
• Open standard (Javasoft)
• Disadvantages
• Open standard
• Existing tools and support (getting better)

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CORBA

• Common Object Request Broker Architecture
• Object communications structure
• Key idea is the ORB - Object Request Broker
• Essentially middleware
• Remote Procedure Calls (RPC)
• Database stored procedures

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Summary

• Components are reusable software objects
• Key is well-defined interfaces
• Design time usage
• Welcome to your future in programming

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Summary

• Have a Happy Thanksgiving