https://github.com/mabe02/lanterna: Java library for creating text-based terminal GUIs
  • Martin Berglund 
/*
 * This file is part of lanterna (https://github.com/mabe02/lanterna).
 * 
 * lanterna is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * 
 * Copyright (C) 2010-2020 Martin Berglund
 */
package com.googlecode.lanterna.gui2;

import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

import com.googlecode.lanterna.Symbols;
import com.googlecode.lanterna.TerminalPosition;
import com.googlecode.lanterna.TerminalSize;
import com.googlecode.lanterna.TerminalTextUtils;
import com.googlecode.lanterna.graphics.ThemeDefinition;
import com.googlecode.lanterna.input.KeyStroke;
import com.googlecode.lanterna.input.KeyType;


Simple labeled button that the user can trigger by pressing the Enter or the Spacebar key on the keyboard when the component is in focus. You can specify an initial action through one of the constructors and you can also add additional actions to the button using addListener(Listener). To remove a previously attached action, use removeListener(Listener). 
Author:Martin
/**
 * Simple labeled button that the user can trigger by pressing the Enter or the Spacebar key on the keyboard when the
 * component is in focus. You can specify an initial action through one of the constructors and you can also add
 * additional actions to the button using {@link #addListener(Listener)}. To remove a previously attached action, use
 * {@link #removeListener(Listener)}.
 * @author Martin
 */
public class Button extends AbstractInteractableComponent<Button> {

    
Listener interface that can be used to catch user events on the button

/**
     * Listener interface that can be used to catch user events on the button
     */
    public interface Listener {
        
This is called when the user has triggered the button

Params:
  • button – Button which was triggered
/**
         * This is called when the user has triggered the button
         * @param button Button which was triggered
         */
        void onTriggered(Button button);
    }

    private final List<Listener> listeners;
    private String label;

    
Creates a new button with a specific label and no initially attached action.

Params:
  • label – Label to put on the button
/**
     * Creates a new button with a specific label and no initially attached action.
     * @param label Label to put on the button
     */
    public Button(String label) {
        this.listeners = new CopyOnWriteArrayList<>();
        setLabel(label);
    }

    
Creates a new button with a label and an associated action to fire when triggered by the user

Params:
  • label – Label to put on the button
  • action – Action to fire when the user triggers the button by pressing the enter or the space key
/**
     * Creates a new button with a label and an associated action to fire when triggered by the user
     * @param label Label to put on the button
     * @param action Action to fire when the user triggers the button by pressing the enter or the space key
     */
    public Button(String label, final Runnable action) {
        this(label);
        listeners.add(button -> action.run());
    }

    @Override
    protected ButtonRenderer createDefaultRenderer() {
        return new DefaultButtonRenderer();
    }

    @Override
    public synchronized TerminalPosition getCursorLocation() {
        return getRenderer().getCursorLocation(this);
    }

    @Override
    public synchronized Result handleKeyStroke(KeyStroke keyStroke) {
        if (isActivationStroke(keyStroke)) {
            triggerActions();
            return Result.HANDLED;
        }
        return super.handleKeyStroke(keyStroke);
    }

    protected synchronized void triggerActions() {
        for(Listener listener: listeners) {
            listener.onTriggered(this);
        }
    }

    
Updates the label on the button to the specified string

Params:
  • label – New label to use on the button
/**
     * Updates the label on the button to the specified string
     * @param label New label to use on the button
     */
    public final synchronized void setLabel(String label) {
        if(label == null) {
            throw new IllegalArgumentException("null label to a button is not allowed");
        }
        if(label.isEmpty()) {
            label = " ";
        }
        this.label = label;
        invalidate();
    }

    
Adds a listener to notify when the button is triggered; the listeners will be called serially in the order they
were added

Params:
  • listener – Listener to call when the button is triggered
/**
     * Adds a listener to notify when the button is triggered; the listeners will be called serially in the order they
     * were added
     * @param listener Listener to call when the button is triggered
     */
    public void addListener(Listener listener) {
        if(listener == null) {
            throw new IllegalArgumentException("null listener to a button is not allowed");
        }
        listeners.add(listener);
    }

    
Removes a listener from the button's list of listeners to call when the button is triggered. If the listener list
doesn't contain the listener specified, this call do with do nothing.

Params:
  • listener – Listener to remove from this button's listener list
Returns:true if this button contained the specified listener
/**
     * Removes a listener from the button's list of listeners to call when the button is triggered. If the listener list
     * doesn't contain the listener specified, this call do with do nothing.
     * @param listener Listener to remove from this button's listener list
     * @return {@code true} if this button contained the specified listener
     */
    public boolean removeListener(Listener listener) {
        return listeners.remove(listener);
    }

    
Returns the label current assigned to the button

Returns:Label currently used by the button
/**
     * Returns the label current assigned to the button
     * @return Label currently used by the button
     */
    public String getLabel() {
        return label;
    }

    @Override
    public String toString() {
        return "Button{" + label + "}";
    }

    
Helper interface that doesn't add any new methods but makes coding new button renderers a little bit more clear

/**
     * Helper interface that doesn't add any new methods but makes coding new button renderers a little bit more clear
     */
    public interface ButtonRenderer extends InteractableRenderer<Button> {
    }

    
This is the default button renderer that is used if you don't override anything. With this renderer, buttons are
drawn on a single line, with the label inside of "<" and ">".

/**
     * This is the default button renderer that is used if you don't override anything. With this renderer, buttons are
     * drawn on a single line, with the label inside of "&lt;" and "&gt;".
     */
    public static class DefaultButtonRenderer implements ButtonRenderer {
        @Override
        public TerminalPosition getCursorLocation(Button button) {
            if(button.getThemeDefinition().isCursorVisible()) {
                return new TerminalPosition(1 + getLabelShift(button, button.getSize()), 0);
            }
            else {
                return null;
            }
        }

        @Override
        public TerminalSize getPreferredSize(Button button) {
            return new TerminalSize(Math.max(8, TerminalTextUtils.getColumnWidth(button.getLabel()) + 2), 1);
        }

        @Override
        public void drawComponent(TextGUIGraphics graphics, Button button) {
            ThemeDefinition themeDefinition = button.getThemeDefinition();
            if(button.isFocused()) {
                graphics.applyThemeStyle(themeDefinition.getActive());
            }
            else {
                graphics.applyThemeStyle(themeDefinition.getInsensitive());
            }
            graphics.fill(' ');
            graphics.setCharacter(0, 0, themeDefinition.getCharacter("LEFT_BORDER", '<'));
            graphics.setCharacter(graphics.getSize().getColumns() - 1, 0, themeDefinition.getCharacter("RIGHT_BORDER", '>'));

            if(button.isFocused()) {
                graphics.applyThemeStyle(themeDefinition.getActive());
            }
            else {
                graphics.applyThemeStyle(themeDefinition.getPreLight());
            }
            int labelShift = getLabelShift(button, graphics.getSize());
            graphics.setCharacter(1 + labelShift, 0, button.getLabel().charAt(0));

            if(TerminalTextUtils.getColumnWidth(button.getLabel()) == 1) {
                return;
            }
            if(button.isFocused()) {
                graphics.applyThemeStyle(themeDefinition.getSelected());
            }
            else {
                graphics.applyThemeStyle(themeDefinition.getNormal());
            }
            graphics.putString(1 + labelShift + 1, 0, button.getLabel().substring(1));
        }

        private int getLabelShift(Button button, TerminalSize size) {
            int availableSpace = size.getColumns() - 2;
            if(availableSpace <= 0) {
                return 0;
            }
            int labelShift = 0;
            int widthInColumns = TerminalTextUtils.getColumnWidth(button.getLabel());
            if(availableSpace > widthInColumns) {
                labelShift = (size.getColumns() - 2 - widthInColumns) / 2;
            }
            return labelShift;
        }
    }

    
Alternative button renderer that displays buttons with just the label and minimal decoration

/**
     * Alternative button renderer that displays buttons with just the label and minimal decoration
     */
    public static class FlatButtonRenderer implements ButtonRenderer {
        @Override
        public TerminalPosition getCursorLocation(Button component) {
            return null;
        }

        @Override
        public TerminalSize getPreferredSize(Button component) {
            return new TerminalSize(TerminalTextUtils.getColumnWidth(component.getLabel()), 1);
        }

        @Override
        public void drawComponent(TextGUIGraphics graphics, Button button) {
            ThemeDefinition themeDefinition = button.getThemeDefinition();
            if(button.isFocused()) {
                graphics.applyThemeStyle(themeDefinition.getActive());
            }
            else {
                graphics.applyThemeStyle(themeDefinition.getInsensitive());
            }
            graphics.fill(' ');
            if(button.isFocused()) {
                graphics.applyThemeStyle(themeDefinition.getSelected());
            }
            else {
                graphics.applyThemeStyle(themeDefinition.getNormal());
            }
            graphics.putString(0, 0, button.getLabel());
        }
    }

    public static class BorderedButtonRenderer implements ButtonRenderer {
        @Override
        public TerminalPosition getCursorLocation(Button component) {
            return null;
        }

        @Override
        public TerminalSize getPreferredSize(Button component) {
            return new TerminalSize(TerminalTextUtils.getColumnWidth(component.getLabel()) + 5, 4);
        }

        @Override
        public void drawComponent(TextGUIGraphics graphics, Button button) {
            ThemeDefinition themeDefinition = button.getThemeDefinition();
            graphics.applyThemeStyle(themeDefinition.getNormal());
            TerminalSize size = graphics.getSize();
            graphics.drawLine(1, 0, size.getColumns() - 3, 0, Symbols.SINGLE_LINE_HORIZONTAL);
            graphics.drawLine(1, size.getRows() - 2, size.getColumns() - 3, size.getRows() - 2, Symbols.SINGLE_LINE_HORIZONTAL);
            graphics.drawLine(0, 1, 0, size.getRows() - 3, Symbols.SINGLE_LINE_VERTICAL);
            graphics.drawLine(size.getColumns() - 2, 1, size.getColumns() - 2, size.getRows() - 3, Symbols.SINGLE_LINE_VERTICAL);
            graphics.setCharacter(0, 0, Symbols.SINGLE_LINE_TOP_LEFT_CORNER);
            graphics.setCharacter(size.getColumns() - 2, 0, Symbols.SINGLE_LINE_TOP_RIGHT_CORNER);
            graphics.setCharacter(size.getColumns() - 2, size.getRows() - 2, Symbols.SINGLE_LINE_BOTTOM_RIGHT_CORNER);
            graphics.setCharacter(0, size.getRows() - 2, Symbols.SINGLE_LINE_BOTTOM_LEFT_CORNER);

            // Fill the inner part of the box
            graphics.drawLine(1, 1, size.getColumns() - 3, 1, ' ');

            // Draw the text inside the button
            if(button.isFocused()) {
                graphics.applyThemeStyle(themeDefinition.getActive());
            }
            graphics.putString(2, 1, TerminalTextUtils.fitString(button.getLabel(), size.getColumns() - 5));

            // Draw the shadow
            graphics.applyThemeStyle(themeDefinition.getInsensitive());
            graphics.drawLine(1, size.getRows() - 1, size.getColumns() - 1, size.getRows() - 1, ' ');
            graphics.drawLine(size.getColumns() - 1, 1, size.getColumns() - 1, size.getRows() - 2, ' ');
        }
    }
}