StateEdit: canRedo() : StateEdit « javax.swing.undo « Java by API

1. Java by API
2. javax.swing.undo
3. StateEdit

StateEdit: canRedo()

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Hashtable;

import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JRadioButton;
import javax.swing.JToggleButton;
import javax.swing.undo.CannotRedoException;
import javax.swing.undo.CannotUndoException;
import javax.swing.undo.StateEdit;
import javax.swing.undo.StateEditable;

public class UndoableToggleApp4 extends JFrame implements StateEditable {

  private JToggleButton tog = new JToggleButton("ToggleButton");

  private JCheckBox cb = new JCheckBox("CheckBox");

  private JRadioButton radio = new JRadioButton("RadioButton");

  private JButton  undoButton = new JButton("Undo");

  private JButton   redoButton = new JButton("Redo");

  private JButton startButton = new JButton("Start");

  private JButton endButton = new JButton("End");

  private StateEdit edit;

  public UndoableToggleApp4() {
    SimpleListener sl = new SimpleListener();
    tog.addActionListener(sl);
    cb.addActionListener(sl);
    radio.addActionListener(sl);

    Box buttonBox = new Box(BoxLayout.Y_AXIS);
    buttonBox.add(tog);
    buttonBox.add(cb);
    buttonBox.add(radio);

    startButton.setEnabled(true);
    endButton.setEnabled(false);
    undoButton.setEnabled(false);
    redoButton.setEnabled(false);

    startButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ev) {
        edit = new StateEdit(UndoableToggleApp4.this);
        startButton.setEnabled(false);
        endButton.setEnabled(true);
        // undoButton.setEnabled(edit.canUndo());
        //
        // NOTE: We really don't want to be able to undo until end() is pressed,
        // but StateEdit does not enforce this for us!
        undoButton.setEnabled(false);
        redoButton.setEnabled(edit.canRedo());
      }
    });

    endButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ev) {
        edit.end();
        startButton.setEnabled(true);
        endButton.setEnabled(false);
        undoButton.setEnabled(edit.canUndo());
        redoButton.setEnabled(edit.canRedo());
      }
    });

    // Add a listener to the undo button. It attempts to call undo() on the
    // current edit, then enables/disables the undo/redo buttons as appropriate.
    undoButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ev) {
        try {
          edit.undo();
        } catch (CannotUndoException ex) {
          ex.printStackTrace();
        } finally {
          undoButton.setEnabled(edit.canUndo());
          redoButton.setEnabled(edit.canRedo());
        }
      }
    });

    redoButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ev) {
        try {
          edit.redo();
        } catch (CannotRedoException ex) {
          ex.printStackTrace();
        } finally {
          undoButton.setEnabled(edit.canUndo());
          redoButton.setEnabled(edit.canRedo());
        }
      }
    });

    // Lay out the state/end and undo/redo buttons.
    Box undoRedoBox = new Box(BoxLayout.X_AXIS);
    undoRedoBox.add(Box.createGlue());
    undoRedoBox.add(startButton);
    undoRedoBox.add(Box.createHorizontalStrut(2));
    undoRedoBox.add(endButton);
    undoRedoBox.add(Box.createHorizontalStrut(2));
    undoRedoBox.add(undoButton);
    undoRedoBox.add(Box.createHorizontalStrut(2));
    undoRedoBox.add(redoButton);
    undoRedoBox.add(Box.createGlue());

    // Lay out the main frame.
    Container content = getContentPane();
    content.setLayout(new BorderLayout());
    content.add(buttonBox, BorderLayout.CENTER);
    content.add(undoRedoBox, BorderLayout.SOUTH);
    setSize(400, 150);
  }

  public class SimpleListener implements ActionListener {
    // When any toggle button is clicked, we turn off the undo and redo
    // buttons, reflecting the fact that we can only undo/redo the last
    // set of state changes as long as no additional changes have been made.
    public void actionPerformed(ActionEvent ev) {
      undoButton.setEnabled(false);
      redoButton.setEnabled(false);
    }
  }

  // Save the state of the app by storing the current state of the three
  // buttons. We'll use the buttons themselves as keys and their selected
  // state as values.
  public void storeState(Hashtable ht) {
    ht.put(tog, new Boolean(tog.isSelected()));
    ht.put(cb, new Boolean(cb.isSelected()));
    ht.put(radio, new Boolean(radio.isSelected()));
  }

  // Restore state based on the values we saved when storeState() was called.
  // Note that StateEdit discards any state info that did not change from
  // between the start state and the end state, so we can't assume that the
  // state for all 3 buttons is in the Hashtable.
  public void restoreState(Hashtable ht) {
    Boolean b1 = (Boolean) ht.get(tog);
    if (b1 != null)
      tog.setSelected(b1.booleanValue());
    Boolean b2 = (Boolean) ht.get(cb);
    if (b2 != null)
      cb.setSelected(b2.booleanValue());
    Boolean b3 = (Boolean) ht.get(radio);
    if (b3 != null)
      radio.setSelected(b3.booleanValue());
  }

  // Main program just creates the frame and displays it.
  public static void main(String[] args) {
    JFrame f = new UndoableToggleApp4();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
  }
}

           
       

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