java - 如何在 swing 中绘制到 JPanel

Question

我正在用 swing 编写一个程序，它使用链接的节点来存储一个值，然后以黄色条的形式将包含的值绘制到 JPanel 中。这幅画最初是使用 AWT 完成的。我读了一点 this关于在 swing 中绘画的教程，但我仍然不明白如何向 JPanel 绘画。该程序应该在按下“随机”按钮时绘制条形图，但目前什么也没画。

我已经包含了我认为相关的代码，但如果您需要任何其他部分，请告诉我。在此先感谢您提供的任何帮助或向我指出的任何教程。

public class DataOrganizer extends JPanel 
    {

        private JFrame  frame;

        protected static final Color DEFAULT_COLOR = Color.YELLOW;

        protected static final Color    HIGHLIGHT_COLOR = Color.YELLOW.darker();

        protected DataCollection<Item> collection; // To hold our items

        protected DataCollection<Item> sortedCollection;

        protected Item selected;

        private final int COLLECTION_SIZE = 10, // Maximum number of items
                MAXIMUM_ITEM_VALUE = 16; // Maximum value of an item

        private int firstItemXCoord;

        protected int   firstItemYCoord;

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

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

        }

        /**
         * Initialize the contents of the frame.
         */
        private void initialize()
        {
            /*
             * Create and set-up the JFrame.
             */
            frame = new JFrame();
            frame.setPreferredSize(new Dimension(550, 450));
            frame.setBounds(100, 100, 600, 400);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.getContentPane().setLayout(null);
            frame.setVisible(true);

            /*
             * Create btnRandom and add an action listener
             * that calls randomAction().
             */
            JButton btnRandom = new JButton("Random");
            btnRandom.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    randomAction();
                }
            });
            btnRandom.setBounds(6, 18, 117, 29);
            frame.getContentPane().add(btnRandom);

            /*
             * Create btnMaximum and add an action listener
             * that calls maximumAction().
             */
            JButton btnMaximum = new JButton("Maximum");
            btnMaximum.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    maximumAction();
                }
            });
            btnMaximum.setBounds(6, 59, 117, 29);
            frame.getContentPane().add(btnMaximum);

            /*
             * Create btnMinimum and add an action listener
             * that calls minimumAction().
             */
            JButton btnMinimum = new JButton("Minimum");
            btnMinimum.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    minimumAction();
                }
            });
            btnMinimum.setBounds(6, 100, 117, 29);
            frame.getContentPane().add(btnMinimum);

            /*
             * Create btnRemove and add an action listener
             * that calls removeAction().
             */
            JButton btnRemove = new JButton("Remove");
            btnRemove.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    removeAction();
                }
            });
            btnRemove.setBounds(6, 141, 117, 29);
            frame.getContentPane().add(btnRemove);

            /*
             * Create btnSort and add an action listener
             * that calls sort().
             */
            JButton btnSort = new JButton("Sort");
            btnSort.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    sort();
                }
            });
            btnSort.setBounds(6, 182, 117, 29);
            frame.getContentPane().add(btnSort);

            /*
             * Create the JPanel, set the bounds,
             * and add it to the frame.
             */
            JPanel panel = new JPanel();
            panel.setBounds(135, 0, 465, 378);
            frame.getContentPane().add(panel);

            //Initialize the unsorted collection
            collection = new DataCollection<Item>(COLLECTION_SIZE);

            //Initialize the sorted collection
            sortedCollection = new DataCollection<Item>(COLLECTION_SIZE);

            repaint();
        }


        public void paintComponent(Graphics panel) {

            super.paintComponent(panel);

            panel.drawString("Hello World", 140 , 10);

            /*
             *  Display the Items when instantiated.
             */

            if (collection != null) 
            { 

                Item item;              
                int xCoord = firstItemXCoord;

                /*
                 * Reset the selected item to the start of the collection,
                 * ensuring it always starts at the first node
                 */
                collection.reset();

                        //While there is another node in the collection, loop through.
                while (collection.hasNext()) 
                {
                    /*
                     * Set the item to the selected node. 
                     * Which since reset() was called on the 
                     * collection, it should be the first node 
                     * in the collection. Then set the next node in the
                     * collection a the selected one.
                     */
                    item = collection.next(); 

                    /*
                     * Call the paint method in the item class
                     */
                    item.paint(panel, xCoord, firstItemXCoord);
                    xCoord += Item.OVERALL_WIDTH;
                }

            }

            /*
             *  Display the Items when instantiated.
             */

            if (sortedCollection != null) 
            { 
                Item item; 
                int xCoord = firstItemXCoord + 200;

                /*
                 * Reset the selected item to the start of the collection,
                 * ensuring it always starts at the first node
                 */
                sortedCollection.reset();

                        //While there is another node in the collection, loop through.
                while (sortedCollection.hasNext()) 
                {
                    /*
                     * Set the item to the selected node. 
                     * Which since reset() was called on the 
                     * sortedCollection, it should be the first node 
                     * in the collection. Then set the next node in the
                     * collection a the selected one.
                     */
                    item = sortedCollection.next(); 

                    /*
                     * Call the paint method in the item class
                     */
                    item.paint(panel, xCoord, firstItemXCoord);
                    xCoord += Item.OVERALL_WIDTH;
                }

            }
        }

        //
        // Random
        //
        public void randomAction() 
        {
            collection.clear(); // We restart with nothing,
            // then we add random items,
            for (int i = 1; i <= COLLECTION_SIZE; i++) 
            {
                collection.add(new Item((int) (1 + MAXIMUM_ITEM_VALUE
                        * Math.random()), DEFAULT_COLOR));
            }
            selected = null; // We make sure nothing is selected
        }

Answer 1

查看 Custom Painting Approaches了解进行自定义绘画的几种方法。

The program is supposed to draw the bars when the "Random" button is pressed,but currently paints nothing

您可能希望使用第一种方法将对象添加到 ArrayList，这样您就有了一个要绘制的对象列表。因此按钮会添加要绘制的对象，然后您调用面板上的 repaint() 方法。