Custom Components

1
Custom Components

• Understand what your users what to accomplish
• Provide the correct UI components
• Several issues when creating custom components
• Do you combine existing components, start from
  scratch, or subclass other components
• Is this a one shot component?
• Do you need to support multiple look and feels?
• How does it react with other components

2
Where does your component come from?

• As you have seen, many Swing components have a
  lot of functionality already built into them
• If you inherit from an existing component, you
  may get a lot of complex behavior
• Tradeoffs
• Inherit from existing Swing GUI component
• Event handling
• Complex behavior
• May support multiple look and feels
• Inherit from JComponent
• You do everything
• May be more efficient
• Could be more work to implement

3
Combining Existing Components

• Safest way to create complex, re-usable
  components.
• Use Existing panels, labels, controls to come up
  with a more complex component.
• Wizard
• SliderPanel (SliderPanel.java, SliderWithReference
  Mark.java)
• ListBuilder (ListBuilder.java)
• Tree or List Panel (ListPanel.java,
  TreePanel.java)

4
FancyLabel

• Wanted to display the following
• Selecting box brings up new window
• Show multi-line text
• Try to make it look nice

Really basic
A little nicer
5
Design decisions

• JButton or JLabel to show
• JLabel
• Need to implement its own mouse listeners
• Supports multi-line, lthtmlgt
• JButton
• Could disable border and draw its own

6
How to implement

• First look at API
• Two candidates, change the renderer or the UI
• Renderer modification
• This almost works, except that the width of the
  displayed text field in the combo box is
  determined by querying each rendered value size.
  
• So if we make the rendered value wider the
  entire component gets wider.
• UI modification
• Look at javax.swing.plaf
• Three methods in class
• Several from ComponentUI
• Not much clues
• Review of BasicComboBoxUI and MetalComboBoxUI
  show little new information

7
Look at source code

• Lots of methods for setting text, icons,
  alignment
• No paint() methods???
• BasicLabelUI to the rescue
• We want this to be a standard JLabel, but with a
  new background.
• So
• Call custom paint first to paint background
• Call super.paint() to paint text!
• FancyLabel.java

8
Example Three state check box

• Common component is a three state check box
• Cleared
• Set
• Indeterminate
• How to approach solution
• Subclass Button
• New component
• Tradeoffs
• Button groups
• Listeners

9
Tri-State Check Box

• There is no easy way to subclass a JCheckBox to
  accomplish this
• AbstractButtons model has two states, no support
  for three
• TriCheckBox.java is one solution
• Written with Java look and feel in mind
• New class, does not inherit from AbstractButton
• Worked great, but one big limitation

10
How TriCheckBox was made

• What did it need to do?
• Display Icon (checkbox)
• Display Text
• Handle HTML as text
• Enable/Disable
• Work with Buttongroup
• Handle listeners
• Initial decision
• Subclass JCheckBox
• Oops!

11
Use JLabel as base

• Provides a lot of support required
• Icon
• Text
• HTML
• Enable/disable
• To make JLabel work we need the following
• MouseListener
• Icon to reflect state
• Event Generator

12
TriCheckBoxIcon

• Found code for drawing Metal LF check box icon
• Created TriCheckBoxIcon class
• Issues
• Great for Metal LF
• Didnt support other LF
• Decision was made to just worry about Metal LF

13
TriCheckBox

• MouseWatcher to listen to mouse events
• Methods to keep track of state
• Methods to support an item listener
• JLabel
• Property listener
• Enable disable
• Looked good, functioned well, had to make a
  ButtonGroup object specifically for the
  TriCheckBox
• Mistake! As JDK 1.5 showed

14
TriCheckBox2

• Need the look and feel of a check box
• Alternate method is to subclass the appropriate
  UI
• Need to subclass all of the appropriate UIs
• JCheckBox
• ButtonModel has two states
• Our model needs three states
• Can ButtonModel be used as a trigger to increment
  our state
• CustomUI that extends the CheckBoxUIs
• Look through API no joy
• Look through MetalCheckBoxUI.java no joy
• Code draws icon then text in one method.
• Calls getDefaultIcon() to get Icon to draw
• Looks like we need to make a custom Icon

15
TriCheckBoxIcon2.java

• The only way to do this properly is to provide
  Icons for all supported LFs
• Metal
• Windows
• Motif
• GTK
• Synth
• Mac
• The Icon is used by the UI class, which is also
  LF based. In the UI, it wants to get model
  information from a ButtonModel.
• We cant use a button model
• So. Need to also write UI classes for all of the
  LF as well
• Decision Very significant effort to implement
  this object correctly. Code still pending.

16
CustomComboBox

• User wanted ComboBox showing small amount of info
  when closed, but extra info when opened
• Used Custom Renderer for combo box
• Used custom objects added to combo box
• CustomComboBox.Location

17
ListBuilder

• Requirement
• Class that lets you build a list of objects, and
  prioritize their order. When done with the
  builder, you can call iterator() to get an
  Iteration of the objects in the list you built.
• There are add and delete buttons, in addition
  there are up and down buttons which move the
  selected item in the list accordingly
• Solution ListBuilder.java
• Combines two JLists, buttons, Iterators and
  several listeners

18
Screen

• Most Screen methods in Java dont work well with
  multiple monitors
• Requirement
• Develop a utility class that allows better
  management of window locations on multiple
  monitors
• Solution Screen.java
• Designed to handle Dual monitor systems
• Additional monitors would require some more
  tweaks to code
• Handles the following cases
• Get number of monitors
• Gets the monitor a java window, or rectangle, is
  in
• Gets the next monitor
• Gets a default monitor
• Centers component on a monitor

19
SliderWithReferenceMark.java

• Requirement
• Create a JSlider with a reference mark on the
  scale. The mark could indicate a default, or
  pre-existing value.
• The reference value should be able to be changed
  at any time
• The reference mark color should be able to be
  changed at any time
• Tooltip text should give what reference value
  currently is
• Should work on all LFs
• Solution
• Modify UI of slider
• Only two UIs used, BasicSliderUI and
  MetalSliderUI