gridlayoutfactory.java

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/*******************************************************************************
 * Copyright (c) 2005, 2006 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jface.layout;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Composite;

/**
 * GridLayoutFactory creates and initializes grid layouts. There are two ways to use GridLayoutFactory.
 * Normally, it is used as a shorthand for writing "new GridLayout()" and initializing a bunch 
 * of fields. In this case the main benefit is a more concise syntax and the ability to create more
 * than one identical GridLayout from the same factory. Changing a property of the factory will affect
 * future layouts created by the factory, but has no effect on layouts that have already been created.
 * 
 * <p>
 * GridLayoutFactory can also generate grid data for all the controls in a layout. This is done with
 * the generateLayout method. To use this feature:
 * </p>
 * 
 * <ol>
 * <li>Create the composite</li>
 * <li>Create all the controls in the composite</li>
 * <li>Call generateLayout</li>
 * </ol>
 * 
 * <p>
 * The order here is important. generateLayout must be called after all the child controls have
 * been created. generateLayout will not change any layout data that has already been attached
 * to a child control and it will not recurse into nested composites. 
 * </p>
 *
 * @since 3.2
 */
public final class GridLayoutFactory {
	
	/**
	 * Template layout. The factory will create copies of this layout. 
	 */
    private GridLayout l;

    /**
     * Creates a new GridLayoutFactory that will create copies of the given layout.
     * 
     * @param l layout to copy
     */
    private GridLayoutFactory(GridLayout l) {
        this.l = l;
    }

    /**
     * Creates a factory that creates copies of the given layout.
     * 
     * @param l layout to copy
     * @return a new GridLayoutFactory instance that creates copies of the given layout
     */
    public static GridLayoutFactory createFrom(GridLayout l) {
    	return new GridLayoutFactory(copyLayout(l));
    }
    
    /**
     * Creates a copy of the reciever.
     * 
     * @return a copy of the reciever
     */
    public GridLayoutFactory copy() {
    	return new GridLayoutFactory(create());
    }
    
    /**
     * Creates a GridLayoutFactory that creates GridLayouts with the default SWT
     * values.
     * 
     * <p>
     * Initial values are:
     * </p>
     * 
     * <ul>
     * <li>numColumns(1)</li>
     * <li>margins(5,5)</li>
     * <li>spacing(5,5)</li>
     * <li>equalWidth(false)</li>
     * </ul>
     * 
     * @return a GridLayoutFactory that creates GridLayouts as though created with
     * their default constructor
     * @see #fillDefaults
     */
    public static GridLayoutFactory swtDefaults() {
    	return new GridLayoutFactory(new GridLayout());
    }

    /**
     * Creates a GridLayoutFactory that creates GridLayouts with no margins and 
     * default dialog spacing.
     * 
     * <p>
     * Initial values are:
     * </p>
     * 
     * <ul>
     * <li>numColumns(1)</li>
     * <li>margins(0,0)</li>
     * <li>spacing(LayoutConstants.getSpacing())</li>
     * <li>equalWidth(false)</li>
     * </ul>
     * 
     * @return a GridLayoutFactory that creates GridLayouts as though created with
     * their default constructor
     * @see #swtDefaults
     */
    public static GridLayoutFactory fillDefaults() {
    	GridLayout layout = new GridLayout();
        layout.marginWidth = 0;
        layout.marginHeight = 0;
        Point defaultSpacing = LayoutConstants.getSpacing();
        layout.horizontalSpacing = defaultSpacing.x;
        layout.verticalSpacing = defaultSpacing.y;
        return new GridLayoutFactory(layout);
    }
    
    /**
     * Sets whether the columns should be forced to be equal width
     * 
     * @param equal true iff the columns should be forced to be equal width
     * @return this
     */
    public GridLayoutFactory equalWidth(boolean equal) {
        l.makeColumnsEqualWidth = equal;
        return this;
    }

    /**
     * Sets the spacing for layouts created with this factory. The spacing
     * is the distance between cells within the layout. 
     * 
     * @param hSpacing horizontal spacing (pixels)
     * @param vSpacing vertical spacing (pixels)
     * @return this
     * @see #margins
     */
    public GridLayoutFactory spacing(int hSpacing, int vSpacing) {
        l.horizontalSpacing = hSpacing;
        l.verticalSpacing = vSpacing;
        return this;
    }

    /**
     * Sets the spacing for layouts created with this factory. The spacing
     * is the distance between cells within the layout. 
     * 
     * @param spacing space between controls in the layout (pixels)
     * @return this
     * @see #margins
     */
    public GridLayoutFactory spacing(Point spacing) {
        l.horizontalSpacing = spacing.x;
        l.verticalSpacing = spacing.y;
        return this;
    }

    /**
     * Sets the margins for layouts created with this factory. The margins
     * are the distance between the outer cells and the edge of the layout.
     * 
     * @param margins margin size (pixels)
     * @return this
     * @see #spacing
     */
    public GridLayoutFactory margins(Point margins) {
        l.marginWidth = margins.x;
        l.marginHeight = margins.y;
        return this;
    }

    /**
     * Sets the margins for layouts created with this factory. The margins
     * are the distance between the outer cells and the edge of the layout.
     * 
     * @param x horizontal margin size (pixels)
     * @param y vertical margin size (pixels)
     * @return this
     * @see #spacing
     */
    public GridLayoutFactory margins(int x, int y) {
        l.marginWidth = x;
        l.marginHeight = y;
        return this;
    }

    /**
     * Sets the number of columns in the layout
     * 
     * @param numColumns number of columns in the layout
     * @return this
     */
    public GridLayoutFactory numColumns(int numColumns) {
        l.numColumns = numColumns;
        return this;
    }

    /**
     * Creates a new GridLayout, and initializes it with values from the factory.
     * 
     * @return a new initialized GridLayout.
     * @see #applyTo
     */
    public GridLayout create() {
        return copyLayout(l);
    }

    /**
     * Creates a new GridLayout and attaches it to the given composite.
     * Does not create the GridData of any of the controls in the composite.
     * 
     * @param c composite whose layout will be set
     * @see #generateLayout
     * @see #create
     * @see GridLayoutFactory
     */
    public void applyTo(Composite c) {
        c.setLayout(copyLayout(l));
    }

    /**
     * Copies the given GridLayout instance
     * 
     * @param l layout to copy
     * @return a new GridLayout
     */
    public static GridLayout copyLayout(GridLayout l) {
        GridLayout result = new GridLayout(l.numColumns, l.makeColumnsEqualWidth);
        result.horizontalSpacing = l.horizontalSpacing;
        result.marginBottom = l.marginBottom;
        result.marginHeight = l.marginHeight;
        result.marginLeft = l.marginLeft;
        result.marginRight = l.marginRight;
        result.marginTop = l.marginTop;
        result.marginWidth = l.marginWidth;
        result.verticalSpacing = l.verticalSpacing;

        return result;
    }

    /**
     * Applies this layout to the given composite, and attaches default GridData
     * to all immediate children that don't have one. The layout is generated using 
     * heuristics based on the widget types. In most cases, it will create exactly the same
     * layout that would have been hardcoded by the programmer. In any situation
     * where it does not produce the desired layout, the GridData for any child can be 
     * overridden by attaching the layout data before calling this method. In these cases,
     * the special-case layout data can be hardcoded and the algorithm can supply defaults
     * to the rest.
     * 
     * <p>
     * This must be called <b>AFTER</b> all of the child controls have been created and their
     * layouts attached. This method will attach a layout to the given composite. If any new 
     * children are created after calling this method, their GridData must be created manually. 
     * The algorithm does not recurse into child composites. To generate all the layouts in
     * a widget hierarchy, the method must be called bottom-up for each Composite.   
     * </p>
     * 
     * <p>
     * All controls are made to span a single cell. The algorithm tries to classify controls into one 
     * of the following categories:
     * </p>
     * 
     * <ul>
     * <li>Pushbuttons: Set to a constant size large enough to fit their text and no smaller
     * than the default button size.</li>
     * <li>Wrapping with text (labels, read-only text boxes, etc.): override the preferred horizontal 
     *     size with the default wrapping point, fill horizontally, grab horizontal space, keep the
     *     preferred vertical size</li>
     * <li>Wrapping without text (toolbars, coolbars, etc.): fill align, don't grab, use the preferred size</li>
     * <li>Horizontally scrolling controls (anything with horizontal scrollbars or where the user edits
     *     text and can cursor through it from left-to-right): override the preferred horizontal size with
     *     a constant, grab horizontal, fill horizontal.</li>
     * <li>Vertically scrolling controls (anything with vertical scrollbars or where the user edits
     *     text and can cursor through it up and down): override the preferred vertical size with a constant,
     *     grab vertical, fill vertical</li>
     * <li>Nested layouts: fill align both directions, grab along any dimension if the layout would
     *     be able to expand along that dimension.</li>
     * <li>Non-wrapping non-scrollable read-only text: fill horizontally, center vertically, default size, don't grab </li>
     * <li>Non-wrapping non-scrollable non-text: fill both, default size, don't grab</li>
     * </ul>
     * 
     * @param c composite whose layout will be generated
     */
    public void generateLayout(Composite c) {
        applyTo(c);
        LayoutGenerator.generateLayout(c);
    }
}