Java: How to reference GUI components from an AbstractAction object?

Question

It is often necessary to change the behavior of other GUI objects depending on the state of another GUI object. For instance. when the button is pressed, the label should change its name. However, when I use an AbstractAction object, for example JButton myButton = new JButton(myButtonAction); , I need a reference to GUI objects in an object that inherits from AbstractAction. Should I just create the AbstractAction objects in the GUI and then pass all the necessary GUI references to the AbstractAction objects, or can this be considered bad style?

To make it more specific:

 // AbstractAction public class MyAction extends AbstractAction { public MyAction(String name, String description, Integer mnemonic, JLabel) { super(name); putValue(SHORT_DESCRIPTION, description); putValue(MNEMONIC_KEY, mnemonic); } public void actionPerformed(ActionEvent e) { // do something } } } public class GUI{ public Action myAction = null; public GUI(){ JLabel label = new JLabel("text"); //This is not a good idea: myAction = new MyAction("some text" , desc, new Integer(KeyEvent.VK_Q), label); JButton myButton = new JButton(myAction); } } 

Answer 1

You want to loosen the clutch as much as possible, and not tighten it, as your question says, and for this I think you should do further abstraction, separating the parts even further from the full MVC program. Then the listener (Action) can change the model, and the view, which is your graphical interface, can listen to the model changes and respond accordingly.

For instance:

 import java.awt.BorderLayout; import java.awt.Component; import java.awt.Dimension; import java.awt.GridBagLayout; import java.awt.event.ActionEvent; import java.awt.event.KeyEvent; import java.beans.PropertyChangeEvent; import java.beans.PropertyChangeListener; import javax.swing.*; import javax.swing.event.SwingPropertyChangeSupport; public class MvcEg { private static void createAndShowGui() { View view = new MvcEgView(); Model model = new MvcEgModel(); new MvcEgControl(model, view); JFrame frame = new JFrame("MvcEg"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().add(view.getMainPanel()); frame.pack(); frame.setLocationByPlatform(true); frame.setVisible(true); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGui(); } }); } } interface View { void setMyButtonAction(Action action); Component getMainPanel(); void setStatusLabelText(String text); } @SuppressWarnings("serial") class MvcEgView implements View { private static final int PREF_W = 500; private static final int PREF_H = 400; private static final String STATUS_TEXT = "Status: "; private JPanel mainPanel = new JPanel() { @Override public Dimension getPreferredSize() { return new Dimension(PREF_W, PREF_H); } }; private JLabel statusLabel = new JLabel(STATUS_TEXT, SwingConstants.CENTER); private JButton myButton = new JButton(); public MvcEgView() { JPanel btnPanel = new JPanel(new GridBagLayout()); btnPanel.add(myButton); mainPanel.setLayout(new BorderLayout()); mainPanel.add(btnPanel, BorderLayout.CENTER); mainPanel.add(statusLabel, BorderLayout.SOUTH); } @Override public void setMyButtonAction(Action action) { myButton.setAction(action); } @Override public void setStatusLabelText(String text) { statusLabel.setText(STATUS_TEXT + text); } @Override public Component getMainPanel() { return mainPanel; } } interface Model { public static final String MOD_FIVE_STATUS = "mod five status"; void incrementStatus(); ModFiveStatus getModFiveStatus(); void removePropertyChangeListener(PropertyChangeListener listener); void addPropertyChangeListener(PropertyChangeListener listener); void setModFiveStatus(ModFiveStatus modFiveStatus); } class MvcEgModel implements Model { private ModFiveStatus modFiveStatus = ModFiveStatus.ZERO; private SwingPropertyChangeSupport pcSupport = new SwingPropertyChangeSupport( this); @Override public void incrementStatus() { int value = modFiveStatus.getValue(); value++; value %= ModFiveStatus.values().length; setModFiveStatus(ModFiveStatus.getValuesStatus(value)); } @Override public void setModFiveStatus(ModFiveStatus modFiveStatus) { ModFiveStatus oldValue = this.modFiveStatus; ModFiveStatus newValue = modFiveStatus; this.modFiveStatus = modFiveStatus; pcSupport.firePropertyChange(MOD_FIVE_STATUS, oldValue, newValue); } @Override public ModFiveStatus getModFiveStatus() { return modFiveStatus; } @Override public void addPropertyChangeListener(PropertyChangeListener listener) { pcSupport.addPropertyChangeListener(listener); } @Override public void removePropertyChangeListener(PropertyChangeListener listener) { pcSupport.removePropertyChangeListener(listener); } } enum ModFiveStatus { ZERO(0, "Zero"), ONE(1, "One"), TWO(2, "Two"), THREE(3, "Three"), FOUR(4, "Four"); private int value; private String text; private ModFiveStatus(int value, String text) { this.value = value; this.text = text; } public int getValue() { return value; } public String getText() { return text; } public static ModFiveStatus getValuesStatus(int value) { if (value < 0 || value >= values().length) { throw new ArrayIndexOutOfBoundsException(value); } for (ModFiveStatus modFiveStatus : ModFiveStatus.values()) { if (modFiveStatus.getValue() == value) { return modFiveStatus; } } // default that should never happen return null; } } @SuppressWarnings("serial") class MvcEgControl { private Model model; private View view; public MvcEgControl(final Model model, final View view) { this.model = model; this.view = view; view.setMyButtonAction(new MyButtonAction("My Button", KeyEvent.VK_B)); view.setStatusLabelText(model.getModFiveStatus().getText()); System.out.println("model status: " + model.getModFiveStatus()); System.out.println("model status text: " + model.getModFiveStatus().getText()); model.addPropertyChangeListener(new ModelListener()); } private class MyButtonAction extends AbstractAction { public MyButtonAction(String text, int mnemonic) { super(text); putValue(MNEMONIC_KEY, mnemonic); } @Override public void actionPerformed(ActionEvent e) { model.incrementStatus(); System.out.println("button pressed"); } } private class ModelListener implements PropertyChangeListener { @Override public void propertyChange(PropertyChangeEvent evt) { if (evt.getPropertyName().equals(Model.MOD_FIVE_STATUS)) { String status = model.getModFiveStatus().getText(); view.setStatusLabelText(status); System.out.println("status is: " + status); } } } } 

The key in my mind is that the Model knows nothing about the representation, and the representation knows little (nothing here) about the model.

Answer 2

Strengthening @Hovercraft's proposed approach will allow your button and shortcut to access a common model. The Action button updates the model and the model notifies the listener, possibly using the PropertyChangeListener , as described here . A more detailed example is shown in specific javax.swing.text.EditorKit implementations that work with the common Document model used by swing text components.