从另一个类运行时，GUI不响应鼠标单击和拖动

Question

I have 2 classes: TestingPanel and SnipIt .

SnipIt is used for selecting an area on the screen.

TestingPanel is the main frame, containing a button to run method Snip() and receiving the return values.

If I test the SnipIt class separately, it works. But if I create a SnipIt object and run method Snip() from TestingPanel class, it doesn't work. The GUI just freezes and doesn't respond to mouse click or drag event. I guess something block the thread handle the mouse events but I'm not sure.

I have been stuck for couple hours and still don't know what caused the issue. Please help.

TestingPanel

package Testing;

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JButton;
import java.awt.BorderLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class TestingPanel {

    private JFrame frame;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    TestingPanel window = new TestingPanel();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public TestingPanel() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 200, 160);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        JButton btnSnip = new JButton("Snip");
        btnSnip.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                getSelectionSize();
            }
        });
        btnSnip.setBounds(47, 87, 89, 23);
        frame.getContentPane().add(btnSnip);
    }

    private void getSelectionSize() {
        int[] size = new int[4];

        Thread worker = new Thread(new Runnable() {
            public void run() {
                SnipIt sn = new SnipIt();
                sn.snip();

                while(!sn.complete) {
                    try {
                        Thread.sleep(800);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }

                size[0] = sn.returnSize()[0];
                size[1] = sn.returnSize()[1];
                size[2] = sn.returnSize()[2];
                size[3] = sn.returnSize()[3];
            }
        });

        worker.start();

        try {
            worker.join();
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }

        System.out.println(size[0] + " " + size[1] + " " + size[2] + " " + size[3]);
    }
}

SnipIt

package Testing;

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Area;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;

public class SnipIt {

    private int recX = 0;
    private int recY = 0;
    private int recWidth = 0;
    private int recHeight = 0;
    public boolean complete = false;

    /*
    public static void main(String [] args)
    {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                SnipIt s = new SnipIt();
                s.snip();
            }
        });
    }
    */

    public void snip() {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception ex) {
        }

        JFrame frame = new JFrame();
        frame.setUndecorated(true);
        frame.setBackground(new Color(0, 0, 0, 0));
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());
        frame.add(new SnipItPane());
        frame.setBounds(getVirtualBounds());
        frame.setVisible(true);
    }

    @SuppressWarnings("serial")
    public class SnipItPane extends JPanel {

        private Point mouseAnchor;
        private Point dragPoint;

        private SelectionPane selectionPane;
        private ControlPane controlPane;

        public SnipItPane() {
            setOpaque(false);
            setLayout(null);
            selectionPane = new SelectionPane();
            controlPane   = new ControlPane();
            add(selectionPane);
            add(controlPane);
            MouseAdapter adapter = new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    mouseAnchor = e.getPoint();
                    dragPoint = null;
                    selectionPane.setLocation(mouseAnchor);
                    selectionPane.setSize(0, 0);
                    controlPane.setLocation(mouseAnchor);
                    controlPane.setSize(0, 0);
                }

                @Override
                public void mouseDragged(MouseEvent e) {
                    dragPoint = e.getPoint();
                    int width = dragPoint.x - mouseAnchor.x;
                    int height = dragPoint.y - mouseAnchor.y;

                    int x = mouseAnchor.x;
                    int y = mouseAnchor.y;

                    if (width < 0) {
                        x = dragPoint.x;
                        width *= -1;
                    }
                    if (height < 0) {
                        y = dragPoint.y;
                        height *= -1;
                    }
                    selectionPane.setBounds(x, y, width, height);
                    selectionPane.revalidate();
                    int controlY = y + height + 5;
                    controlPane.setBounds(x, controlY, width, 25);
                    controlPane.revalidate();
                    repaint();
                }
            };
            addMouseListener(adapter);
            addMouseMotionListener(adapter);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            Graphics2D g2d = (Graphics2D) g.create();

            Rectangle bounds = new Rectangle(0, 0, getWidth(), getHeight());
            Area area = new Area(bounds);
            area.subtract(new Area(selectionPane.getBounds()));

            g2d.setColor(new Color(102, 102, 102, 80));
            g2d.fill(area);

        }
    }

    @SuppressWarnings("serial")
    public class ControlPane extends JPanel {
        private JButton btnClose;

        public ControlPane() {
            setOpaque(false);
            btnClose = new JButton("Save");
            setLayout(new BorderLayout());
            this.add(btnClose, BorderLayout.NORTH);

            btnClose.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    complete = true;
                    SwingUtilities.getWindowAncestor(ControlPane.this).dispose();
                }
            });
        }
    }


    @SuppressWarnings("serial")
    public class SelectionPane extends JPanel {

        public SelectionPane() {
            setOpaque(false);

            addComponentListener(new ComponentAdapter() {
                @Override
                public void componentResized(ComponentEvent e) {
                    recX = getX();
                    recY = getY();
                    recWidth = getWidth();
                    recHeight = getHeight();
                }
            });
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            float strokeWidth = 1.0f;
            float dash1[] = {10.0f};
            BasicStroke dashed =
                    new BasicStroke(strokeWidth,
                    BasicStroke.CAP_BUTT,
                    BasicStroke.JOIN_MITER,
                    10.0f, dash1, 0.0f);
            g2d.setColor(Color.BLACK);
            g2d.setStroke(dashed);
            g2d.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
            g2d.dispose();
        }
    }

    public static Rectangle getVirtualBounds() {
        Rectangle bounds = new Rectangle(0, 0, 0, 0);

        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice lstGDs[] = ge.getScreenDevices();
        for (GraphicsDevice gd : lstGDs) {
            bounds.add(gd.getDefaultConfiguration().getBounds());
        }
        return bounds;
    }

    public int[] returnSize() {
        int[] size = new int[4];
        size[0] = recX;
        size[1] = recY;
        size[2] = recWidth;
        size[3] = recHeight;
        return size;
    }
}

Answer 1

You're running the Snipit application in a background thread and then freezing that thread with Thread.sleep and a while true block, something guaranteed to freeze the GUI. Read Lesson: Concurrency in Swing and then be sure to always run Swing applications on the single Swing event thread, and do any long running or sleeping code in a background thread.

Possible solutions to your issue:

• Make the Snipit window an undecorated modal dialog. This way program flow from the calling code stops when the dialog is visible and resumes when no longer visible.
• Or Make the Snipit window JFrame an instance field of the class and allow outside classes to add listeners to it so that they will be notified when it closes.

eg,

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dialog.ModalityType;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Area;

import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;

public class TestSnipit {

    private static void createAndShowGui() {
        boolean runTest = true;

        if (runTest) {
            TestingPanel.main(null);
        } else {
            SnipIt.main(null);
        }
    }

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

class TestingPanel {

    private JFrame frame;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    TestingPanel window = new TestingPanel();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public TestingPanel() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 200, 160);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        JButton btnSnip = new JButton("Snip");
        btnSnip.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                getSelectionSize();
            }
        });
        btnSnip.setBounds(47, 87, 89, 23);
        frame.getContentPane().add(btnSnip);
    }

    private void getSelectionSize() {
        int[] size = new int[4];

        // !!
        SnipIt sn = new SnipIt();
        sn.snip(frame);

        // Thread worker = new Thread(new Runnable() {
        // public void run() {
        // SnipIt sn = new SnipIt();
        // sn.snip();
        //
        // while (!sn.complete) {
        // try {
        // Thread.sleep(800);
        // } catch (InterruptedException e) {
        // e.printStackTrace();
        // }
        // }
        //

        size[0] = sn.returnSize()[0];
        size[1] = sn.returnSize()[1];
        size[2] = sn.returnSize()[2];
        size[3] = sn.returnSize()[3];

        // }
        // });
        //
        // worker.start();
        //
        // try {
        // worker.join();
        // } catch (InterruptedException e1) {
        // e1.printStackTrace();
        // }

        System.out.println(size[0] + " " + size[1] + " " + size[2] + " " + size[3]);
    }
}

class SnipIt {

    private int recX = 0;
    private int recY = 0;
    private int recWidth = 0;
    private int recHeight = 0;
    public boolean complete = false;

    public static void main(String[] args) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                SnipIt s = new SnipIt();
                s.snip(null); // !!
            }
        });
    }

    public void snip(Window owner) { // !!
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception ex) {
        }

        // JFrame frame = new JFrame();
        JDialog frame = new JDialog(owner, null, ModalityType.APPLICATION_MODAL); // !!
        frame.setUndecorated(true);
        frame.setBackground(new Color(0, 0, 0, 0));
        // frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE); // !!
        frame.setLayout(new BorderLayout());
        frame.add(new SnipItPane());
        frame.setBounds(getVirtualBounds());
        frame.setVisible(true);
    }

    @SuppressWarnings("serial")
    public class SnipItPane extends JPanel {

        private Point mouseAnchor;
        private Point dragPoint;

        private SelectionPane selectionPane;
        private ControlPane controlPane;

        public SnipItPane() {
            setOpaque(false);
            setLayout(null);
            selectionPane = new SelectionPane();
            controlPane = new ControlPane();
            add(selectionPane);
            add(controlPane);
            MouseAdapter adapter = new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    mouseAnchor = e.getPoint();
                    dragPoint = null;
                    selectionPane.setLocation(mouseAnchor);
                    selectionPane.setSize(0, 0);
                    controlPane.setLocation(mouseAnchor);
                    controlPane.setSize(0, 0);
                }

                @Override
                public void mouseDragged(MouseEvent e) {
                    dragPoint = e.getPoint();
                    int width = dragPoint.x - mouseAnchor.x;
                    int height = dragPoint.y - mouseAnchor.y;

                    int x = mouseAnchor.x;
                    int y = mouseAnchor.y;

                    if (width < 0) {
                        x = dragPoint.x;
                        width *= -1;
                    }
                    if (height < 0) {
                        y = dragPoint.y;
                        height *= -1;
                    }
                    selectionPane.setBounds(x, y, width, height);
                    selectionPane.revalidate();
                    int controlY = y + height + 5;
                    controlPane.setBounds(x, controlY, width, 25);
                    controlPane.revalidate();
                    repaint();
                }
            };
            addMouseListener(adapter);
            addMouseMotionListener(adapter);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            Graphics2D g2d = (Graphics2D) g.create();

            Rectangle bounds = new Rectangle(0, 0, getWidth(), getHeight());
            Area area = new Area(bounds);
            area.subtract(new Area(selectionPane.getBounds()));

            g2d.setColor(new Color(102, 102, 102, 80));
            g2d.fill(area);

        }
    }

    @SuppressWarnings("serial")
    public class ControlPane extends JPanel {
        private JButton btnClose;

        public ControlPane() {
            setOpaque(false);
            btnClose = new JButton("Save");
            setLayout(new BorderLayout());
            this.add(btnClose, BorderLayout.NORTH);

            btnClose.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    complete = true;
                    SwingUtilities.getWindowAncestor(ControlPane.this).dispose();
                }
            });
        }
    }

    @SuppressWarnings("serial")
    public class SelectionPane extends JPanel {

        public SelectionPane() {
            setOpaque(false);

            addComponentListener(new ComponentAdapter() {
                @Override
                public void componentResized(ComponentEvent e) {
                    recX = getX();
                    recY = getY();
                    recWidth = getWidth();
                    recHeight = getHeight();
                }
            });
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            float strokeWidth = 1.0f;
            float dash1[] = { 10.0f };
            BasicStroke dashed = new BasicStroke(strokeWidth, BasicStroke.CAP_BUTT,
                    BasicStroke.JOIN_MITER, 10.0f, dash1, 0.0f);
            g2d.setColor(Color.BLACK);
            g2d.setStroke(dashed);
            g2d.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
            g2d.dispose();
        }
    }

    public static Rectangle getVirtualBounds() {
        Rectangle bounds = new Rectangle(0, 0, 0, 0);

        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice lstGDs[] = ge.getScreenDevices();
        for (GraphicsDevice gd : lstGDs) {
            bounds.add(gd.getDefaultConfiguration().getBounds());
        }
        return bounds;
    }

    public int[] returnSize() {
        int[] size = new int[4];
        size[0] = recX;
        size[1] = recY;
        size[2] = recWidth;
        size[3] = recHeight;
        return size;
    }
}

A side issue unrelated to your initial problem is your use of null layougs. While null layouts and setBounds() might seem to Swing newbies like the easiest and best way to create complex GUI's, the more Swing GUI'S you create the more serious difficulties you will run into when using them. They won't resize your components when the GUI resizes, they are a royal witch to enhance or maintain, they fail completely when placed in scrollpanes, they look gawd-awful when viewed on all platforms or screen resolutions that are different from the original one.