Java Swing - Lecture 3 Layout Management

1
Java Swing - Lecture 3Layout Management

• Boriana Koleva
• (bnk_at_cs.nott.ac.uk)

2
Where are we up to?

• Last Time
• Containers (Frames and Dialogs)
• Hierarchy
• Root Panes
• Layered Panes
• Content Panes
• Glass Panes
• Components
• Lots of em
• Today
• The exciting topic of Layout Management

3
Laying out components

• Manage realized components
• Determine size and position
• Each container has a layout manager
• (usually)

4
Layout managers general aspects

• Creating a layout manager
• Consulting managers
• Types of managers
• Choosing managers
• Other features of component layout
• All Covered very well here
• http//java.sun.com/docs/books/tutorial/uiswing/la
  yout/using.html

5
Creating a layout manager

• Default layout managers
• JFrame, JDialog, JApplet have BorderLayout
• JPanel has FlowLayout
• Except when used as a Content Pane (Border
  Layout)
• Setting the layout manager for a container
• JFrame frame new JFrame()
• frame.setLayout(new FlowLayout())
• JPanel contentPane new JPanel()
• contentPane.setLayout(new BorderLayout())

6
Consulting layout managers (1)

• Consulted automatically when container may need
  to change its appearance.
• These methods result in consultation, but DONT
  trigger new layout
• add(), remove(), removeAll()
• getAlignmentX(), getAlignmentY()
• getPreferredSize(), getMinimumSize(),
  getMaximumSize()

7
Consulting layout managers (2)

• These methods actually result in the manager
  performing layout.
• JFrame.pack()
• Causes this Window to be sized to fit the
  preferred size and layouts of its subcomponents.
• JFrame.show() JFrame.setVisible(true)
• Shows the component
• JComponent.revalidate()
• This method will automatically be called on this
  component when a property value changes. Looks
  for all dependent components and calls validate()
  on them. Validate() causes a container to lay
  out its subcomponents again

8
Layout managers - types

• BorderLayout
• BoxLayout
• FlowLayout
• GridLayout
• GridBagLayout
• CardLayout

9
BorderLayout

• Five areas
• NORTH, SOUTH, EAST, WEST and CENTER
• Not all areas must be used
• Do not assume a default area for components
• Centre gets as much area as possible
• Specify location as argument of add method
• pane.setLayout(new BorderLayout())
• pane.add(new JButton(Button 1 (NORTH)),
  BorderLayout.NORTH)
• Setting gaps between components (default 0)
• BorderLayout.setHgap(int gap)
• BorderLayout.setVgap(int gap)
• BorderLayout(int horizontalGap, int verticalGap)
  - Constructor

10
BoxLayout (1)

• Components on top / next to each other
• Direction is your choice
• Tries to size components at preferred height for
  Y_AXIS or width for X_AXIS
• Width as largest component width
• See above picture

11
BoxLayout (2)

• Space fillers
• Rigid - fixed-size space between two components
• Glue - taking up no space unless you pull apart
  the components that it's sticking to. Helps
  reposition extra space (default is at end)
• Custom - Use this to specify a component with
  whatever minimum, preferred, and maximum sizes
  you want

12
BoxLayout (3)

• Component sizes
• Respect Max, Min and Preferred Sizes of
  components
• Alignment
• Comes into play when not all components are the
  same width
• Can specify Left (0), Centre (0.5) or Right (1).
  Or Top Middle Bottom
• If you are having layout problems, first treat as
  an Alignment issue, then examine sizes.

13
FlowLayout

• Very simple - JPanels default
• Components in row(s)
• At preferred size
• Alignment
• FlowLayout.LEFT
• FlowLayout.CENTRE
• FlowLayout.RIGHT
• Gaps
• Default 5
• Specifying - setter hGap vGap methods or via
  constructor

14
GridLayout

• Grid of cells - all same size
• Components take all space in a cell
• Gaps
• default 5
• use setter methods hGap and vGap
• or via arguments to constructor
• Re-sizing
• Cells resize to be as large as possible in given
  window / container

15
GridBagLayout (1)

• Very flexible (and complex!)
• Rows can have different heights
• Columns can have different lengths
• Uses cells in a grid

GridBagLayout gridbag new GridBagLayout() GridB
agConstraints c new GridBagConstraints() JPane
l pane new JPanel() pane.setLayout(gridbag) /
/--- For each component to be added to this
container //--- ...Create the component... //---
...Set instance variables in the
GridBagConstraints instance... gridbag.setConstrai
nts(theComponent, c) pane.add(theComponent)
16
GridBagLayout (2)

• Constraints
• set in an instance of a gridBagConstraints Object
• gridx and gridy - The row and column of the upper
  left of the component
• Anchor - Where to display within cell when
  component is smaller than it
• fill - How to size component when cell is larger
  than components requested size
• insets - External padding - min space between
  component and cell edges
• ipadx, ipady - Internal padding - What to add to
  min size of components
• weightx and weighty - How to distribute extra
  space (padding)
• gridwidth and gridheight - Number of columns or
  rows the component uses
• More explanation here
• http//java.sun.com/docs/books/tutorial/uiswing/la
  yout/gridbagConstraints.html
• Example explained very well here
• http//java.sun.com/docs/books/tutorial/uiswing/la
  yout/gridbagExample.html

17
CardLayout

• Manages objects (usually JPanels) in sets
• Works much like tabbed pane
• Choose cards by
• Asking for card in order added to container
• Going backwards or forwards
• Specifying card by name

18
Choosing layout managers (1)

• In order to display a component in as much space
  as it can get, consider
• BorderLayout
• Component in centre
• GridBagLayout
• fillGridBagConstraints.BOTH
• BoxLayout
• Component specifies very large preferred/maximum
  sizes

19
Choosing layout managers (2)

• To display a few components in a compact row
• JPanels default FlowLayout
• BoxLayout
• Display a few components of the same size in rows
  and columns
• GridLayout

20
Choosing layout managers (3)

• Display a few components in a row or column, with
  different spacing between them and custom
  component sizes
• BoxLayout
• Display a complex layout that has many components
• GridBagLayout
• Using JPanel grouping and hierarchies

21
Layout managers - other layout features

• Absolute positioning of components
• When
• How
• Customising layout managers
• When
• How

22
Absolute positioning (1)

• Dont do it unless
• component size isnt affected by container size
  or font looknfeel changes
• e.g. desktop panes containing internal frames
• custom container performs size position
  calculations particular to container
• e.g. split panes

23
Absolute positioning (2)

• Key points from NoneWindow.java
• Instruct window to use no Layout
• .contentPane.setLayout(null)
• Set components size and position with
• XYZ.setBounds(x, y, width, height)
• Set window size with
• window.setSize(x, y)

24
Custom layout managers (1)

• Ensure no existing manager does the job
• GridBagLayout / BoxLayout
• Layout manager downloads
• If your trying to do it, chances are someone else
  has done it already
• DECLARE use of external code in coursework

25
Custom layout managers (2)

• Create class which implements Layout Manager
  interface
• e.g. public class myManager implements
  LayoutManager
• Must have 5 methods required by interface
• void addLayoutComponent(String, Component)
• void removeLayoutComponent(Component)
• Dimension preferredLayoutSize(Container)
• Dimension minimumLayoutSize(Container)
• void layoutContainer(Container)
• See below URL for more documentation
• http//java.sun.com/docs/books/tutorial/uiswing/la
  yout/custom.html

26
Summary

• Creating a layout manager
• Consulting managers
• Types of managers
• BorderLayout GridLayout
• BoxLayout GridBagLayout
• FlowLayout CardLayout
• Choosing managers
• Absolute positioning
• Custom layout managers
• Next time Event handling and event listeners