java swing - lecture 3 layout management

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Java Swing - Lecture 3Layout Management

Boriana Koleva([email protected])

G5BUID - Java Swing - 2005

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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”


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Laying out components

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

(usually)


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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/layout/

using.html


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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());


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Consulting layout managers (1)

• Consulted automatically when container may need to change its appearance.

• These methods result in consultation, but DON’T trigger new layout add(), remove(), removeAll() getAlignmentX(), getAlignmentY() getPreferredSize(), getMinimumSize(), getMaximumSize()


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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


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Layout managers - types

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


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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


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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


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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


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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.


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FlowLayout

• Very simple - JPanel’s 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


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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


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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();GridBagConstraints c = new GridBagConstraints();

JPanel 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.setConstraints(theComponent, c);pane.add(theComponent);


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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/layout/gridbagConstraints.html

• Example explained very well here: http://java.sun.com/docs/books/tutorial/uiswing/layout/gridbagExample.html


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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


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Choosing layout managers (1)

• In order to display a component in as much space as it can get, consider: BorderLayout

Component in centre

GridBagLayout fill=GridBagConstraints.BOTH

BoxLayout Component specifies very large

preferred/maximum sizes


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• To display a few components in a compact row: JPanel’s default FlowLayout BoxLayout

• Display a few components of the same size in rows and columns GridLayout


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• 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


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Layout managers - other layout features

• Absolute positioning of components When How

• Customising layout managers When How


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Absolute positioning (1)

• Don’t do it; unless…

component size isn’t affected by container size or font & look’n’feel changes e.g. desktop panes containing internal frames

custom container performs size & position calculations particular to container e.g. split panes


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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);


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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


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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/layout/custom.html


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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

java swing - lecture 3 layout management

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