org.eclipse.swt.widgets.ScrollBar.java Source code

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/*******************************************************************************
 * Copyright (c) 2000, 2016 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.widgets;

import org.eclipse.swt.*;
import org.eclipse.swt.events.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.internal.*;
import org.eclipse.swt.internal.gtk.*;

/**
 * Instances of this class are selectable user interface
 * objects that represent a range of positive, numeric values.
 * <p>
 * At any given moment, a given scroll bar will have a
 * single 'selection' that is considered to be its
 * value, which is constrained to be within the range of
 * values the scroll bar represents (that is, between its
 * <em>minimum</em> and <em>maximum</em> values).
 * </p><p>
 * Typically, scroll bars will be made up of five areas:</p>
 * <ol>
 * <li>an arrow button for decrementing the value</li>
 * <li>a page decrement area for decrementing the value by a larger amount</li>
 * <li>a <em>thumb</em> for modifying the value by mouse dragging</li>
 * <li>a page increment area for incrementing the value by a larger amount</li>
 * <li>an arrow button for incrementing the value</li>
 * </ol>
 * <p>
 * Based on their style, scroll bars are either <code>HORIZONTAL</code>
 * (which have a left facing button for decrementing the value and a
 * right facing button for incrementing it) or <code>VERTICAL</code>
 * (which have an upward facing button for decrementing the value
 * and a downward facing buttons for incrementing it).
 * </p><p>
 * On some platforms, the size of the scroll bar's thumb can be
 * varied relative to the magnitude of the range of values it
 * represents (that is, relative to the difference between its
 * maximum and minimum values). Typically, this is used to
 * indicate some proportional value such as the ratio of the
 * visible area of a document to the total amount of space that
 * it would take to display it. SWT supports setting the thumb
 * size even if the underlying platform does not, but in this
 * case the appearance of the scroll bar will not change.
 * </p><p>
 * Scroll bars are created by specifying either <code>H_SCROLL</code>,
 * <code>V_SCROLL</code> or both when creating a <code>Scrollable</code>.
 * They are accessed from the <code>Scrollable</code> using
 * <code>getHorizontalBar</code> and <code>getVerticalBar</code>.
 * </p><p>
 * Note: Scroll bars are not Controls.  On some platforms, scroll bars
 * that appear as part of some standard controls such as a text or list
 * have no operating system resources and are not children of the control.
 * For this reason, scroll bars are treated specially.  To create a control
 * that looks like a scroll bar but has operating system resources, use
 * <code>Slider</code>.
 * </p>
 * <dl>
 * <dt><b>Styles:</b></dt>
 * <dd>HORIZONTAL, VERTICAL</dd>
 * <dt><b>Events:</b></dt>
 * <dd>Selection</dd>
 * </dl>
 * <p>
 * Note: Only one of the styles HORIZONTAL and VERTICAL may be specified.
 * </p><p>
 * IMPORTANT: This class is <em>not</em> intended to be subclassed.
 * </p>
 *
 * @see Slider
 * @see Scrollable
 * @see Scrollable#getHorizontalBar
 * @see Scrollable#getVerticalBar
 * @see <a href="http://www.eclipse.org/swt/examples.php">SWT Example: ControlExample</a>
 * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
 * @noextend This class is not intended to be subclassed by clients.
 */
public class ScrollBar extends Widget {
    Scrollable parent;
    long adjustmentHandle;
    int detail;
    boolean dragSent;

    ScrollBar() {
    }

    /**
    * Creates a new instance of the widget.
    */
    ScrollBar(Scrollable parent, int style) {
        super(parent, checkStyle(style));
        this.parent = parent;
        createWidget(0);
    }

    /**
     * Adds the listener to the collection of listeners who will
     * be notified when the user changes the receiver's value, by sending
     * it one of the messages defined in the <code>SelectionListener</code>
     * interface.
     * <p>
     * When <code>widgetSelected</code> is called, the event object detail field contains one of the following values:
     * <code>SWT.NONE</code> - for the end of a drag.
     * <code>SWT.DRAG</code>.
     * <code>SWT.HOME</code>.
     * <code>SWT.END</code>.
     * <code>SWT.ARROW_DOWN</code>.
     * <code>SWT.ARROW_UP</code>.
     * <code>SWT.PAGE_DOWN</code>.
     * <code>SWT.PAGE_UP</code>.
     * <code>widgetDefaultSelected</code> is not called.
     * </p>
     *
     * @param listener the listener which should be notified when the user changes the receiver's value
     *
     * @exception IllegalArgumentException <ul>
     *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
     * </ul>
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see SelectionListener
     * @see #removeSelectionListener
     * @see SelectionEvent
     */
    public void addSelectionListener(SelectionListener listener) {
        checkWidget();
        if (listener == null)
            error(SWT.ERROR_NULL_ARGUMENT);
        TypedListener typedListener = new TypedListener(listener);
        addListener(SWT.Selection, typedListener);
        addListener(SWT.DefaultSelection, typedListener);
    }

    static int checkStyle(int style) {
        return checkBits(style, SWT.HORIZONTAL, SWT.VERTICAL, 0, 0, 0, 0);
    }

    @Override
    void deregister() {
        super.deregister();
        if (adjustmentHandle != 0)
            display.removeWidget(adjustmentHandle);
    }

    void destroyHandle() {
        super.destroyWidget();
    }

    @Override
    void destroyWidget() {
        parent.destroyScrollBar(this);
        releaseHandle();
        //parent.sendEvent (SWT.Resize);
    }

    /**
     * Returns <code>true</code> if the receiver is enabled, and
     * <code>false</code> otherwise. A disabled control is typically
     * not selectable from the user interface and draws with an
     * inactive or "grayed" look.
     *
     * @return the receiver's enabled state
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see #isEnabled
     */
    public boolean getEnabled() {
        checkWidget();
        if (handle != 0)
            return GTK.gtk_widget_get_sensitive(handle);
        return true;
    }

    /**
     * Returns the amount that the receiver's value will be
     * modified by when the up/down (or right/left) arrows
     * are pressed.
     *
     * @return the increment
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public int getIncrement() {
        checkWidget();
        return (int) GTK.gtk_adjustment_get_step_increment(adjustmentHandle);
    }

    /**
     * Returns the maximum value which the receiver will allow.
     *
     * @return the maximum
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public int getMaximum() {
        checkWidget();
        return (int) GTK.gtk_adjustment_get_upper(adjustmentHandle);
    }

    /**
     * Returns the minimum value which the receiver will allow.
     *
     * @return the minimum
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public int getMinimum() {
        checkWidget();
        return (int) GTK.gtk_adjustment_get_lower(adjustmentHandle);
    }

    /**
     * Returns the amount that the receiver's value will be
     * modified by when the page increment/decrement areas
     * are selected.
     *
     * @return the page increment
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public int getPageIncrement() {
        checkWidget();
        return (int) GTK.gtk_adjustment_get_page_increment(adjustmentHandle);
    }

    /**
     * Returns the receiver's parent, which must be a Scrollable.
     *
     * @return the receiver's parent
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public Scrollable getParent() {
        checkWidget();
        return parent;
    }

    /**
     * Returns the single 'selection' that is the receiver's value.
     *
     * @return the selection
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public int getSelection() {
        checkWidget();
        return (int) GTK.gtk_adjustment_get_value(adjustmentHandle);
    }

    /**
     * Returns a point describing the receiver's size. The
     * x coordinate of the result is the width of the receiver.
     * The y coordinate of the result is the height of the
     * receiver.
     *
     * @return the receiver's size
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public Point getSize() {
        checkWidget();
        return DPIUtil.autoScaleDown(getSizeInPixels());
    }

    Point getSizeInPixels() {
        checkWidget();
        if (handle == 0)
            return new Point(0, 0);
        GtkRequisition requisition = new GtkRequisition();
        gtk_widget_get_preferred_size(handle, requisition);
        return new Point(requisition.width, requisition.height);
    }

    /**
     * Returns the receiver's thumb value.
     *
     * @return the thumb value
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see ScrollBar
     */
    public int getThumb() {
        checkWidget();
        return (int) GTK.gtk_adjustment_get_page_size(adjustmentHandle);
    }

    /**
     * Returns a rectangle describing the size and location of the
     * receiver's thumb relative to its parent.
     *
     * @return the thumb bounds, relative to the {@link #getParent() parent}
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @since 3.6
     */
    public Rectangle getThumbBounds() {
        checkWidget();
        return DPIUtil.autoScaleDown(getThumbBoundsInPixels());
    }

    Rectangle getThumbBoundsInPixels() {
        checkWidget();
        int[] slider_start = new int[1], slider_end = new int[1];
        gtk_range_get_slider_range(handle, slider_start, slider_end);
        int x, y, width, height;
        GtkAllocation allocation = new GtkAllocation();
        GTK.gtk_widget_get_allocation(handle, allocation);
        if ((style & SWT.VERTICAL) != 0) {
            x = allocation.x;
            y = slider_start[0];
            width = allocation.width;
            height = slider_end[0] - slider_start[0];
        } else {
            x = slider_start[0];
            y = allocation.y;
            width = slider_end[0] - slider_start[0];
            height = allocation.height;
        }
        Rectangle rect = new Rectangle(x, y, width, height);
        int[] origin_x = new int[1], origin_y = new int[1];
        if (GTK.GTK4) {
            long surface = gtk_widget_get_surface(parent.scrolledHandle);
            if (surface != 0)
                GDK.gdk_surface_get_origin(surface, origin_x, origin_y);
            rect.x += origin_x[0];
            rect.y += origin_y[0];
            surface = gtk_widget_get_surface(parent.handle);
            if (surface != 0)
                GDK.gdk_surface_get_origin(surface, origin_x, origin_y);
            rect.x -= origin_x[0];
            rect.y -= origin_y[0];
        } else {
            long window = gtk_widget_get_window(parent.scrolledHandle);
            if (window != 0)
                GDK.gdk_window_get_origin(window, origin_x, origin_y);
            rect.x += origin_x[0];
            rect.y += origin_y[0];
            window = gtk_widget_get_window(parent.handle);
            if (window != 0)
                GDK.gdk_window_get_origin(window, origin_x, origin_y);
            rect.x -= origin_x[0];
            rect.y -= origin_y[0];
        }
        return rect;
    }

    /**
     * Returns a rectangle describing the size and location of the
     * receiver's thumb track relative to its parent. This rectangle
     * comprises the areas 2, 3, and 4 as described in {@link ScrollBar}.
     *
     * @return the thumb track bounds, relative to the {@link #getParent() parent}
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @since 3.6
     */
    public Rectangle getThumbTrackBounds() {
        checkWidget();
        return DPIUtil.autoScaleDown(getThumbTrackBoundsInPixels());
    }

    Rectangle getThumbTrackBoundsInPixels() {
        checkWidget();
        int x = 0, y = 0, width, height;
        int[] has_stepper = new int[1];
        boolean hasB = false, hasB2 = false, hasF = false, hasF2 = false;
        /*
         * Only GTK3 scrollbars have steppers, even non-overlay scrollbars in
         * GTK4 do not have steppers.
         */
        if (!GTK.GTK4) {
            GTK.gtk_widget_style_get(handle, OS.has_backward_stepper, has_stepper, 0);
            hasB = has_stepper[0] != 0;
            GTK.gtk_widget_style_get(handle, OS.has_secondary_backward_stepper, has_stepper, 0);
            hasB2 = has_stepper[0] != 0;
            GTK.gtk_widget_style_get(handle, OS.has_forward_stepper, has_stepper, 0);
            hasF = has_stepper[0] != 0;
            GTK.gtk_widget_style_get(handle, OS.has_secondary_forward_stepper, has_stepper, 0);
            hasF2 = has_stepper[0] != 0;
        }
        GtkAllocation allocation = new GtkAllocation();
        GTK.gtk_widget_get_allocation(handle, allocation);
        if ((style & SWT.VERTICAL) != 0) {
            int stepperSize = allocation.width;
            x = allocation.x;
            if (hasB)
                y += stepperSize;
            if (hasF2)
                y += stepperSize;
            width = allocation.width;
            height = allocation.height - y;
            if (hasB2)
                height -= stepperSize;
            if (hasF)
                height -= stepperSize;
            if (height < 0) {
                int[] slider_start = new int[1], slider_end = new int[1];
                gtk_range_get_slider_range(handle, slider_start, slider_end);
                y = slider_start[0];
                height = 0;
            }
        } else {
            int stepperSize = allocation.height;
            if (hasB)
                x += stepperSize;
            if (hasF2)
                x += stepperSize;
            y = allocation.y;
            width = allocation.width - x;
            if (hasB2)
                width -= stepperSize;
            if (hasF)
                width -= stepperSize;
            height = allocation.height;
            if (width < 0) {
                int[] slider_start = new int[1], slider_end = new int[1];
                gtk_range_get_slider_range(handle, slider_start, slider_end);
                x = slider_start[0];
                width = 0;
            }
        }
        Rectangle rect = new Rectangle(x, y, width, height);
        int[] origin_x = new int[1], origin_y = new int[1];
        if (GTK.GTK4) {
            long surface = gtk_widget_get_surface(parent.scrolledHandle);
            if (surface != 0)
                GDK.gdk_surface_get_origin(surface, origin_x, origin_y);
            rect.x += origin_x[0];
            rect.y += origin_y[0];
            surface = gtk_widget_get_surface(parent.handle);
            if (surface != 0)
                GDK.gdk_surface_get_origin(surface, origin_x, origin_y);
            rect.x -= origin_x[0];
            rect.y -= origin_y[0];
        } else {
            long window = gtk_widget_get_window(parent.scrolledHandle);
            if (window != 0)
                GDK.gdk_window_get_origin(window, origin_x, origin_y);
            rect.x += origin_x[0];
            rect.y += origin_y[0];
            window = gtk_widget_get_window(parent.handle);
            if (window != 0)
                GDK.gdk_window_get_origin(window, origin_x, origin_y);
            rect.x -= origin_x[0];
            rect.y -= origin_y[0];
        }
        return rect;
    }

    /**
     * Returns <code>true</code> if the receiver is visible, and
     * <code>false</code> otherwise.
     * <p>
     * If one of the receiver's ancestors is not visible or some
     * other condition makes the receiver not visible, this method
     * may still indicate that it is considered visible even though
     * it may not actually be showing.
     * </p>
     *
     * @return the receiver's visibility state
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public boolean getVisible() {
        checkWidget();
        long scrolledHandle = parent.scrolledHandle;
        int[] hsp = new int[1], vsp = new int[1];
        GTK.gtk_scrolled_window_get_policy(scrolledHandle, hsp, vsp);
        if ((style & SWT.HORIZONTAL) != 0) {
            return hsp[0] != GTK.GTK_POLICY_NEVER && hsp[0] != GTK.GTK_POLICY_EXTERNAL
                    && GTK.gtk_widget_get_visible(handle);
        } else {
            return vsp[0] != GTK.GTK_POLICY_NEVER && vsp[0] != GTK.GTK_POLICY_EXTERNAL
                    && GTK.gtk_widget_get_visible(handle);
        }
    }

    @Override
    long gtk_event(long widget, long event) {
        if (!GTK.GTK4)
            return 0;
        int eventType = GDK.gdk_event_get_event_type(event);
        switch (eventType) {
        case GDK.GDK4_BUTTON_PRESS: {
            return gtk_button_press_event(widget, event);
        }
        case GDK.GDK4_BUTTON_RELEASE: {
            return gtk_button_release_event(widget, event);
        }
        }
        return 0;
    }

    @Override
    long gtk_button_press_event(long widget, long eventPtr) {
        long result = super.gtk_button_press_event(widget, eventPtr);
        if (result != 0)
            return result;
        detail = GTK.GTK_SCROLL_NONE;
        dragSent = false;
        return result;
    }

    @Override
    long gtk_change_value(long widget, long scroll, long value1, long value2) {
        detail = (int) scroll;
        return 0;
    }

    void gtk_range_get_slider_range(long widget, int[] slider_start, int[] slider_end) {
        GTK.gtk_range_get_slider_range(widget, slider_start, slider_end);
    }

    @Override
    long gtk_value_changed(long adjustment) {
        Event event = new Event();
        dragSent = detail == GTK.GTK_SCROLL_JUMP;
        switch (detail) {
        case GTK.GTK_SCROLL_NONE:
            event.detail = SWT.NONE;
            break;
        case GTK.GTK_SCROLL_JUMP:
            event.detail = SWT.DRAG;
            break;
        case GTK.GTK_SCROLL_START:
            event.detail = SWT.HOME;
            break;
        case GTK.GTK_SCROLL_END:
            event.detail = SWT.END;
            break;
        case GTK.GTK_SCROLL_PAGE_DOWN:
        case GTK.GTK_SCROLL_PAGE_RIGHT:
        case GTK.GTK_SCROLL_PAGE_FORWARD:
            event.detail = SWT.PAGE_DOWN;
            break;
        case GTK.GTK_SCROLL_PAGE_UP:
        case GTK.GTK_SCROLL_PAGE_LEFT:
        case GTK.GTK_SCROLL_PAGE_BACKWARD:
            event.detail = SWT.PAGE_UP;
            break;
        case GTK.GTK_SCROLL_STEP_DOWN:
        case GTK.GTK_SCROLL_STEP_RIGHT:
        case GTK.GTK_SCROLL_STEP_FORWARD:
            event.detail = SWT.ARROW_DOWN;
            break;
        case GTK.GTK_SCROLL_STEP_UP:
        case GTK.GTK_SCROLL_STEP_LEFT:
        case GTK.GTK_SCROLL_STEP_BACKWARD:
            event.detail = SWT.ARROW_UP;
            break;
        }
        if (!dragSent)
            detail = GTK.GTK_SCROLL_NONE;
        sendSelectionEvent(SWT.Selection, event, false);
        parent.updateScrollBarValue(this);
        GTK.gtk_widget_queue_draw(parent.handle);
        return 0;
    }

    @Override
    long gtk_event_after(long widget, long gdkEvent) {
        int eventType = GDK.gdk_event_get_event_type(gdkEvent);
        eventType = Control.fixGdkEventTypeValues(eventType);
        switch (eventType) {
        case GDK.GDK_BUTTON_RELEASE: {
            int[] eventButton = new int[1];
            GDK.gdk_event_get_button(gdkEvent, eventButton);
            if (eventButton[0] == 1 && detail == GTK.GTK_SCROLL_JUMP) {
                if (!dragSent) {
                    Event event = new Event();
                    event.detail = SWT.DRAG;
                    sendSelectionEvent(SWT.Selection, event, false);
                }
                sendSelectionEvent(SWT.Selection);
            }
            detail = GTK.GTK_SCROLL_NONE;
            dragSent = false;
            break;
        }
        }
        return super.gtk_event_after(widget, gdkEvent);
    }

    @Override
    void hookEvents() {
        super.hookEvents();
        OS.g_signal_connect_closure(adjustmentHandle, OS.value_changed, display.getClosure(VALUE_CHANGED), false);
        if (GTK.GTK4) {
            // GTK4: event-after replaced with generic event
            OS.g_signal_connect_closure_by_id(handle, display.signalIds[EVENT], 0, display.getClosure(EVENT),
                    false);
            // GTK4: change-value moved to gtk_scroll_child in Composite
        } else {
            OS.g_signal_connect_closure(handle, OS.change_value, display.getClosure(CHANGE_VALUE), false);
            OS.g_signal_connect_closure_by_id(handle, display.signalIds[BUTTON_PRESS_EVENT], 0,
                    display.getClosure(BUTTON_PRESS_EVENT), false);
            OS.g_signal_connect_closure_by_id(handle, display.signalIds[EVENT_AFTER], 0,
                    display.getClosure(EVENT_AFTER), false);
        }
    }

    /**
     * Returns <code>true</code> if the receiver is enabled and all
     * of the receiver's ancestors are enabled, and <code>false</code>
     * otherwise. A disabled control is typically not selectable from the
     * user interface and draws with an inactive or "grayed" look.
     *
     * @return the receiver's enabled state
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see #getEnabled
     */
    public boolean isEnabled() {
        checkWidget();
        return getEnabled() && getParent().getEnabled();
    }

    /**
     * Returns <code>true</code> if the receiver is visible and all
     * of the receiver's ancestors are visible and <code>false</code>
     * otherwise.
     *
     * @return the receiver's visibility state
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see #getVisible
     */
    public boolean isVisible() {
        checkWidget();
        return getVisible() && getParent().isVisible();
    }

    @Override
    void register() {
        super.register();
        if (adjustmentHandle != 0)
            display.addWidget(adjustmentHandle, this);
    }

    @Override
    void releaseHandle() {
        super.releaseHandle();
        parent = null;
    }

    @Override
    void releaseParent() {
        super.releaseParent();
        if (parent.horizontalBar == this)
            parent.horizontalBar = null;
        if (parent.verticalBar == this)
            parent.verticalBar = null;
    }

    /**
     * Removes the listener from the collection of listeners who will
     * be notified when the user changes the receiver's value.
     *
     * @param listener the listener which should no longer be notified
     *
     * @exception IllegalArgumentException <ul>
     *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
     * </ul>
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see SelectionListener
     * @see #addSelectionListener
     */
    public void removeSelectionListener(SelectionListener listener) {
        checkWidget();
        if (listener == null)
            error(SWT.ERROR_NULL_ARGUMENT);
        if (eventTable == null)
            return;
        eventTable.unhook(SWT.Selection, listener);
        eventTable.unhook(SWT.DefaultSelection, listener);
    }

    /**
     * Enables the receiver if the argument is <code>true</code>,
     * and disables it otherwise. A disabled control is typically
     * not selectable from the user interface and draws with an
     * inactive or "grayed" look.
     *
     * @param enabled the new enabled state
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setEnabled(boolean enabled) {
        checkWidget();
        if (handle != 0)
            GTK.gtk_widget_set_sensitive(handle, enabled);
    }

    /**
     * Sets the amount that the receiver's value will be
     * modified by when the up/down (or right/left) arrows
     * are pressed to the argument, which must be at least
     * one.
     *
     * @param value the new increment (must be greater than zero)
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setIncrement(int value) {
        checkWidget();
        if (value < 1)
            return;
        OS.g_signal_handlers_block_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
        GTK.gtk_adjustment_set_step_increment(adjustmentHandle, value);
        OS.g_signal_handlers_unblock_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
    }

    /**
     * Sets the maximum. If this value is negative or less than or
     * equal to the minimum, the value is ignored. If necessary, first
     * the thumb and then the selection are adjusted to fit within the
     * new range.
     *
     * @param value the new maximum
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setMaximum(int value) {
        checkWidget();
        GtkAdjustment adjustment = new GtkAdjustment();
        gtk_adjustment_get(adjustmentHandle, adjustment);
        int minimum = (int) adjustment.lower;
        if (value <= minimum)
            return;
        adjustment.upper = value;
        adjustment.page_size = Math.min((int) adjustment.page_size, value - minimum);
        adjustment.value = Math.min((int) adjustment.value, (int) (value - adjustment.page_size));
        OS.g_signal_handlers_block_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
        GTK.gtk_adjustment_configure(adjustmentHandle, adjustment.value, adjustment.lower, adjustment.upper,
                adjustment.step_increment, adjustment.page_increment, adjustment.page_size);
        OS.g_signal_handlers_unblock_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
    }

    /**
     * Sets the minimum value. If this value is negative or greater
     * than or equal to the maximum, the value is ignored. If necessary,
     * first the thumb and then the selection are adjusted to fit within
     * the new range.
     *
     * @param value the new minimum
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setMinimum(int value) {
        checkWidget();
        if (value < 0)
            return;
        GtkAdjustment adjustment = new GtkAdjustment();
        gtk_adjustment_get(adjustmentHandle, adjustment);
        int maximum = (int) adjustment.upper;
        if (value >= maximum)
            return;
        adjustment.lower = value;
        adjustment.page_size = Math.min((int) adjustment.page_size, maximum - value);
        adjustment.value = Math.max((int) adjustment.value, value);
        OS.g_signal_handlers_block_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
        GTK.gtk_adjustment_configure(adjustmentHandle, adjustment.value, adjustment.lower, adjustment.upper,
                adjustment.step_increment, adjustment.page_increment, adjustment.page_size);
        OS.g_signal_handlers_unblock_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
    }

    @Override
    void setOrientation(boolean create) {
        super.setOrientation(create);
        if ((parent.style & SWT.MIRRORED) != 0 || !create) {
            if ((parent.state & CANVAS) != 0) {
                if ((style & SWT.HORIZONTAL) != 0) {
                    GTK.gtk_range_set_inverted(handle, (parent.style & SWT.RIGHT_TO_LEFT) != 0);
                }
            }
        }
    }

    /**
     * Sets the amount that the receiver's value will be
     * modified by when the page increment/decrement areas
     * are selected to the argument, which must be at least
     * one.
     *
     * @param value the page increment (must be greater than zero)
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setPageIncrement(int value) {
        checkWidget();
        if (value < 1)
            return;
        OS.g_signal_handlers_block_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
        GTK.gtk_adjustment_set_page_increment(adjustmentHandle, value);
        OS.g_signal_handlers_unblock_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
    }

    /**
     * Sets the single <em>selection</em> that is the receiver's
     * value to the argument which must be greater than or equal
     * to zero.
     *
     * @param selection the new selection (must be zero or greater)
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setSelection(int selection) {
        checkWidget();
        selection = Math.min(selection, getMaximum() - getThumb());
        OS.g_signal_handlers_block_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
        GTK.gtk_adjustment_set_value(adjustmentHandle, selection);
        OS.g_signal_handlers_unblock_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
    }

    /**
     * Sets the thumb value. The thumb value should be used to represent
     * the size of the visual portion of the current range. This value is
     * usually the same as the page increment value.
     * <p>
     * This new value will be ignored if it is less than one, and will be
     * clamped if it exceeds the receiver's current range.
     * </p>
     *
     * @param value the new thumb value, which must be at least one and not
     * larger than the size of the current range
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setThumb(int value) {
        checkWidget();
        if (value < 1)
            return;
        GtkAdjustment adjustment = new GtkAdjustment();
        gtk_adjustment_get(adjustmentHandle, adjustment);
        value = (int) Math.min(value, (int) (adjustment.upper - adjustment.lower));
        adjustment.page_size = (double) value;
        adjustment.value = Math.min((int) adjustment.value, (int) (adjustment.upper - value));
        OS.g_signal_handlers_block_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
        GTK.gtk_adjustment_configure(adjustmentHandle, adjustment.value, adjustment.lower, adjustment.upper,
                adjustment.step_increment, adjustment.page_increment, adjustment.page_size);
        OS.g_signal_handlers_unblock_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
    }

    /**
     * Sets the receiver's selection, minimum value, maximum
     * value, thumb, increment and page increment all at once.
     * <p>
     * Note: This is similar to setting the values individually
     * using the appropriate methods, but may be implemented in a
     * more efficient fashion on some platforms.
     * </p>
     *
     * @param selection the new selection value
     * @param minimum the new minimum value
     * @param maximum the new maximum value
     * @param thumb the new thumb value
     * @param increment the new increment value
     * @param pageIncrement the new pageIncrement value
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setValues(int selection, int minimum, int maximum, int thumb, int increment, int pageIncrement) {
        checkWidget();
        if (minimum < 0)
            return;
        if (maximum < 0)
            return;
        if (thumb < 1)
            return;
        if (increment < 1)
            return;
        if (pageIncrement < 1)
            return;
        thumb = Math.min(thumb, maximum - minimum);
        GtkAdjustment adjustment = new GtkAdjustment();
        adjustment.lower = minimum;
        adjustment.upper = maximum;
        adjustment.step_increment = increment;
        adjustment.page_increment = pageIncrement;
        adjustment.page_size = thumb;
        adjustment.value = Math.min(Math.max(selection, minimum), maximum - thumb);
        OS.g_signal_handlers_block_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
        GTK.gtk_adjustment_configure(adjustmentHandle, adjustment.value, adjustment.lower, adjustment.upper,
                adjustment.step_increment, adjustment.page_increment, adjustment.page_size);
        /*
         * gtk_adujustment_value_changed is deprecated on GTK3.18+.
         * GTK+ will emit "value-changed" itself whenever the value changes.
         * See bug 495413.
         */
        if (GTK.GTK_VERSION < OS.VERSION(3, 18, 0))
            GTK.gtk_adjustment_value_changed(adjustmentHandle);
        OS.g_signal_handlers_unblock_matched(adjustmentHandle, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, VALUE_CHANGED);
    }

    /**
     * Marks the receiver as visible if the argument is <code>true</code>,
     * and marks it invisible otherwise.
     * <p>
     * If one of the receiver's ancestors is not visible or some
     * other condition makes the receiver not visible, marking
     * it visible may not actually cause it to be displayed.
     * </p>
     *
     * @param visible the new visibility state
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     */
    public void setVisible(boolean visible) {
        checkWidget();
        if (parent.setScrollBarVisible(this, visible)) {
            sendEvent(visible ? SWT.Show : SWT.Hide);
            parent.sendEvent(SWT.Resize);
        }
    }

}