Add image thumbnails to a layout in a grid?

Question

I have a list of images. I need to add as small thumbnails to a frame. I currently have frame with SpringLayout. How can add thumbnails in some grid like fashio

Answer 1

So basically, you need some kind of container that lives in the scroll pane (commonly known as the view).

To this you should add your images.

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class ImageGrid {

    public static void main(String[] args) {
        new ImageGrid();
    }

    public ImageGrid() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JPanel imagesPane;

        public TestPane() {
            setLayout(new BorderLayout());
            imagesPane = new JPanel(new WrapLayout());
            add(new JScrollPane(imagesPane));
            JButton scan = new JButton("Scan");
            scan.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    String path = "C:\\Users\\shane\\Dropbox\\Ponies";
                    File[] files = new File(path).listFiles(new FileFilter() {
                        @Override
                        public boolean accept(File pathname) {
                            String name = pathname.getName().toLowerCase();
                            return pathname.isFile() && (name.endsWith(".png")
                                    || name.endsWith(".jpg")
                                    || name.endsWith(".gif"));
                        }
                    });
                    imagesPane.removeAll();
                    for (File file : files) {
                        try {
                            ImagePane pane = new ImagePane(file);
                            imagesPane.add(pane);
                        } catch (Exception exp) {
                            exp.printStackTrace();
                        }
                    }
                    imagesPane.revalidate();
                    imagesPane.repaint();
                }
            });
            add(scan, BorderLayout.SOUTH);
        }
    }

    public class ImagePane extends JPanel {

        private Image img;

        public ImagePane(File source) throws IOException {
            img = ImageIO.read(source);
            if (img.getWidth(this) > 200 || img.getHeight(this) > 200) {
                int width = img.getWidth(this);
                int height = img.getWidth(this);
                float scaleWidth = 200f / width;
                float scaleHeight = 200f / height;
                if (scaleWidth > scaleHeight) {
                    width = -1;
                    height = (int)(height * scaleHeight);
                } else {
                    width = (int)(width * scaleWidth);
                    height = -1;
                }
                img = img.getScaledInstance(width, height, Image.SCALE_SMOOTH);
            }
        }

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

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            if (img != null) {
//                int width = img.getWidth();
//                int height = img.getHeight();
//                float scale = 1f;
//                AffineTransform at = new AffineTransform();
//                at.translate(
//                        (getWidth() / 2) - ((img.getWidth() * scale) / 2),
//                        (getHeight() / 2) - ((img.getHeight() * scale) / 2));
//                at.scale(scale, scale);
//                g2d.setTransform(at);
                g2d.drawImage(img, 0, 0, this);
            }
            g2d.dispose();
        }
    }

    /**
     * FlowLayout subclass that fully supports wrapping of components.
     */
    public class WrapLayout extends FlowLayout {

        private Dimension preferredLayoutSize;

        /**
         * Constructs a new
         * WrapLayout with a left alignment and a default 5-unit
         * horizontal and vertical gap.
         */
        public WrapLayout() {
            super();
        }

        /**
         * Constructs a new
         * FlowLayout with the specified alignment and a default 5-unit
         * horizontal and vertical gap. The value of the alignment argument must be
         * one of
         * WrapLayout,
         * WrapLayout, or
         * WrapLayout.
         *
         * @param align the alignment value
         */
        public WrapLayout(int align) {
            super(align);
        }

        /**
         * Creates a new flow layout manager with the indicated alignment and the
         * indicated horizontal and vertical gaps.
         * 

         * The value of the alignment argument must be one of
         * WrapLayout,
         * WrapLayout, or
         * WrapLayout.
         *
         * @param align the alignment value
         * @param hgap the horizontal gap between components
         * @param vgap the vertical gap between components
         */
        public WrapLayout(int align, int hgap, int vgap) {
            super(align, hgap, vgap);
        }

        /**
         * Returns the preferred dimensions for this layout given the
         * visible components in the specified target container.
         *
         * @param target the component which needs to be laid out
         * @return the preferred dimensions to lay out the subcomponents of the
         * specified container
         */
        @Override
        public Dimension preferredLayoutSize(Container target) {
            return layoutSize(target, true);
        }

        /**
         * Returns the minimum dimensions needed to layout the visible
         * components contained in the specified target container.
         *
         * @param target the component which needs to be laid out
         * @return the minimum dimensions to lay out the subcomponents of the
         * specified container
         */
        @Override
        public Dimension minimumLayoutSize(Container target) {
            Dimension minimum = layoutSize(target, false);
            minimum.width -= (getHgap() + 1);
            return minimum;
        }

        /**
         * Returns the minimum or preferred dimension needed to layout the target
         * container.
         *
         * @param target target to get layout size for
         * @param preferred should preferred size be calculated
         * @return the dimension to layout the target container
         */
        private Dimension layoutSize(Container target, boolean preferred) {
            synchronized (target.getTreeLock()) {
                //  Each row must fit with the width allocated to the containter.
                //  When the container width = 0, the preferred width of the container
                //  has not yet been calculated so lets ask for the maximum.

                int targetWidth = target.getSize().width;

                if (targetWidth == 0) {
                    targetWidth = Integer.MAX_VALUE;
                }

                int hgap = getHgap();
                int vgap = getVgap();
                Insets insets = target.getInsets();
                int horizontalInsetsAndGap = insets.left + insets.right + (hgap * 2);
                int maxWidth = targetWidth - horizontalInsetsAndGap;

                //  Fit components into the allowed width

                Dimension dim = new Dimension(0, 0);
                int rowWidth = 0;
                int rowHeight = 0;

                int nmembers = target.getComponentCount();

                for (int i = 0; i < nmembers; i++) {
                    Component m = target.getComponent(i);

                    if (m.isVisible()) {
                        Dimension d = preferred ? m.getPreferredSize() : m.getMinimumSize();

                        //  Can't add the component to current row. Start a new row.

                        if (rowWidth + d.width > maxWidth) {
                            addRow(dim, rowWidth, rowHeight);
                            rowWidth = 0;
                            rowHeight = 0;
                        }

                        //  Add a horizontal gap for all components after the first

                        if (rowWidth != 0) {
                            rowWidth += hgap;
                        }

                        rowWidth += d.width;
                        rowHeight = Math.max(rowHeight, d.height);
                    }
                }

                addRow(dim, rowWidth, rowHeight);

                dim.width += horizontalInsetsAndGap;
                dim.height += insets.top + insets.bottom + vgap * 2;

                //    When using a scroll pane or the DecoratedLookAndFeel we need to
                //  make sure the preferred size is less than the size of the
                //  target containter so shrinking the container size works
                //  correctly. Removing the horizontal gap is an easy way to do this.

                Container scrollPane = SwingUtilities.getAncestorOfClass(JScrollPane.class, target);

                if (scrollPane != null && target.isValid()) {
                    dim.width -= (hgap + 1);
                }

                return dim;
            }
        }

        /*
         *  A new row has been completed. Use the dimensions of this row
         *  to update the preferred size for the container.
         *
         *  @param dim update the width and height when appropriate
         *  @param rowWidth the width of the row to add
         *  @param rowHeight the height of the row to add
         */
        private void addRow(Dimension dim, int rowWidth, int rowHeight) {
            dim.width = Math.max(dim.width, rowWidth);

            if (dim.height > 0) {
                dim.height += getVgap();
            }

            dim.height += rowHeight;
        }
    }
}

This example includes WrapLayout. The scaling is done for speed and simplicity, but the method used is unavisable, take a look at this for a better method.

I would normally load and scale the images in a background thread, like a SwingWorker, but this is an example of the idea.