A Swing layout able to lay pages horizontally inside an horizontally scrollable panel

PrintPreviewPagesTester.java

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Insets;
import java.awt.LayoutManager;
import java.awt.Rectangle;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.ScrollPaneConstants;
import javax.swing.Scrollable;
import javax.swing.SwingUtilities;

import lombok.extern.slf4j.Slf4j;

@Slf4j
public class PrintPreviewPagesTester {

	public PrintPreviewPagesTester() {
		JFrame frame = new JFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		PrintPreviewPagesController controller = new PrintPreviewPagesController();

		Container contentPane = frame.getContentPane();
		Component pagesPanel = controller.getPagesPanel();
		contentPane.add(pagesPanel, BorderLayout.CENTER);
		Component actionPanel = controller.getActionPanel();
		contentPane.add(actionPanel, BorderLayout.SOUTH);

		frame.setVisible(true);
		frame.setSize(300, 400);
		frame.setState(Frame.MAXIMIZED_BOTH);
	}

	public static void main(String[] args) {
		SwingUtilities.invokeLater(() -> new PrintPreviewPagesTester());
	}

	public class PrintPreviewPagesPanel {
		private JScrollPane	mainView;
		private JPanel		pagesPanel;

		public PrintPreviewPagesPanel() {
			pagesPanel = new ScrollablePanel(new PrintPreviewPagesLayout());
			mainView = new JScrollPane(pagesPanel);
			mainView.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED);
			mainView.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER);
			mainView.addComponentListener(new ComponentListener() {

				@Override
				public void componentShown(ComponentEvent e) {
				}

				@Override
				public void componentResized(ComponentEvent e) {
					updatePagesPanelSize();		// first update the size of the pages panel...
					//					pagesPanel.doLayout();		// ... then resize the pages inside
				}

				@Override
				public void componentMoved(ComponentEvent e) {
				}

				@Override
				public void componentHidden(ComponentEvent e) {
				}
			});
		}

		public Component getComponent() {
			return mainView;
		}

		private void updatePagesPanelSize() {
			int mainViewHeight = mainView.getHeight();
			int mainViewWidth = mainView.getWidth();
			log.info("mainViewWidth={} - mainViewHeight={}", mainViewWidth, mainViewHeight);

			int pagesPanelTargetHeight = mainViewHeight;
			int pagesPanelTargetWidth = -1;
			if (pagesPanel.getComponentCount() >= 1) {
				Rectangle lastComponentBounds = pagesPanel.getComponent(pagesPanel.getComponentCount() - 1).getBounds();
				pagesPanelTargetWidth = lastComponentBounds.width + lastComponentBounds.x;
			} else {
				pagesPanelTargetWidth = mainViewWidth;
			}

			Dimension pagesPanelTargetDimension = new Dimension(pagesPanelTargetWidth, pagesPanelTargetHeight);
			log.info("pagesPanelTargetDimension={}", pagesPanelTargetDimension);
			pagesPanel.setPreferredSize(pagesPanelTargetDimension);
			pagesPanel.setSize(pagesPanelTargetDimension);
		}

		public void addPage(JPanel newPage) {
			pagesPanel.add(newPage);
			//			mainView.invalidate();
			updatePagesPanelSize();		// first resize the panel (with wrong content but to position the height)
			pagesPanel.doLayout();		// then do a layout pass to position the pages (their setBounds method will be called)...
			updatePagesPanelSize();		// .. then resize the pagesPanel to match its content
		}

	}

	public class PrintPreviewPagesLayout implements LayoutManager {

		public PrintPreviewPagesLayout() {
		}

		@Override
		public void addLayoutComponent(String arg0, Component arg1) {
		}

		@Override
		public void layoutContainer(Container parent) {
			Insets insets = parent.getInsets();
			//	        int maxWidth = parent.getWidth() - (insets.left + insets.right);
			int targetHeight = parent.getHeight() - (insets.top + insets.bottom);

			int currentHorizontalPosition = 0;
			int nbComponents = parent.getComponentCount();
			for (int i = 0; i < nbComponents; i++) {
				Component comp = parent.getComponent(i);
				Dimension compPreferredSize = comp.getPreferredSize();
				log.info("targetHeight: {} ", targetHeight);
				double targetWidth = (compPreferredSize.getWidth() * targetHeight) / compPreferredSize.getHeight();
				comp.setBounds(currentHorizontalPosition, 0, (int) targetWidth, targetHeight);
				log.info("Component Bounds: {}+{} ", currentHorizontalPosition, targetWidth);
				currentHorizontalPosition += targetWidth;
			}
			//			parent.setPreferredSize(new Dimension(currentHorizontalPosition, targetHeight));
		}

		@Override
		public Dimension minimumLayoutSize(Container parent) {
			return preferredLayoutSize(parent);
		}

		@Override
		public Dimension preferredLayoutSize(Container parent) {
			return new Dimension(10, 10);
		}

		@Override
		public void removeLayoutComponent(Component parent) {
		}

	}

	public class PrintPreviewPagesController {

		/** 1st view of the controller */
		private PrintPreviewPagesPanel	pagesPanel;
		/** 2nd view of the controller */
		private JPanel					actionPanel;
		/** last color used to color a page */
		private Color					lastColor	= new Color(50, 100, 150);

		public PrintPreviewPagesController() {
			pagesPanel = new PrintPreviewPagesPanel();
			actionPanel = buildActionPanel();
		}

		public Component getPagesPanel() {
			return pagesPanel.getComponent();
		}

		public Component getActionPanel() {
			return actionPanel;
		}

		private JPanel buildActionPanel() {
			JPanel panel = new JPanel();
			panel.setBackground(Color.darkGray);
			JButton button = new JButton("add page");
			button.addActionListener(event -> addPage());
			panel.add(button);
			return panel;
		}

		private void addPage() {
			JPanel newPage = createNewPage();
			pagesPanel.addPage(newPage);
		}

		private JPanel createNewPage() {
			lastColor = new Color(
					modifyColorComponent(lastColor.getRed()),
					modifyColorComponent(lastColor.getGreen()),
					modifyColorComponent(lastColor.getBlue()));
			JPanel newPage = new JPanel();
			newPage.setBorder(BorderFactory.createLineBorder(Color.black, 10));
			newPage.setBackground(lastColor);
			newPage.setPreferredSize(new Dimension(20, 30));
			return newPage;
		}

		private int modifyColorComponent(int value) {
			return (value + 50) % 255;
		}

	}

	/** see http://stackoverflow.com/questions/10331129/jscrollpane-resize-containing-jpanel-when-scrollbars-appear */
	public class ScrollablePanel extends JPanel implements Scrollable {

		public ScrollablePanel(PrintPreviewPagesLayout printPreviewPagesLayout) {
			super(printPreviewPagesLayout);
			setBackground(Color.cyan);
		}

		@Override
		public Dimension getPreferredScrollableViewportSize() {
			return new Dimension(200, 200);
		}

		@Override
		public int getScrollableBlockIncrement(Rectangle arg0, int arg1, int arg2) {
			return 100;
		}

		@Override
		public boolean getScrollableTracksViewportHeight() {
			return true;
		}

		@Override
		public boolean getScrollableTracksViewportWidth() {
			return false;
		}

		@Override
		public int getScrollableUnitIncrement(Rectangle arg0, int arg1, int arg2) {
			return 100;
		}

	}

}