什么是“ Paint and repaint”功能的替代方案？

Question

在Java中是否有任何可以用paint()和repaint()替換的函數。

我有一個場景。

有一個三角形（三角形1） 。 當用戶單擊三角形時，將出現另一個三角形（三角形2），並且第一個（三角形1）將從屏幕上刪除。 （使用JFrame ， paint()和repaint()編碼）

到目前為止，我已經做到了。 但是問題是當我使用鼠標最小化或更改窗口的大小作為輸出窗口時，它只是再次繪制了Triangle 1而不是Triangle 2 。 或者如果我調用g2d.clearRect(0, 0, 1000, 1000);
triangle.reset();則清除整個屏幕g2d.clearRect(0, 0, 1000, 1000);
triangle.reset(); g2d.clearRect(0, 0, 1000, 1000);
triangle.reset();

注意：這兩個功能都將刪除先前的三角形（三角形1）。

是否有任何功能不應在最小化或更改窗口大小時更改狀態？

或者我們可以根據情況重寫repaint()或任何有幫助的內容。

這是工作代碼。 執行它，單擊三角形，然后最小化並再次查看。 您將更清楚地了解問題。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Triangle_shape extends JFrame implements ActionListener {

    public static JButton btnSubmit = new JButton("Submit");

    public Triangle_shape() {
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
        frame.setLayout(new BorderLayout());
        frame.add(new TrianglePanel(), BorderLayout.CENTER);
        frame.add(btnSubmit, BorderLayout.PAGE_END);
        frame.pack();
        frame.repaint();
        frame.setTitle("A Test Frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public static class TrianglePanel extends JPanel implements MouseListener {

        private Polygon triangle, triangle2;

        public TrianglePanel() {
            //Create triangle
            triangle = new Polygon();
            triangle.addPoint(400, 550);        //left   
            triangle.addPoint(600, 550); //right
            triangle.addPoint(500, 350); //top

            //Add mouse Listener
            addMouseListener(this);

            //Set size to make sure that the whole triangle is shown
            setPreferredSize(new Dimension(300, 300));
        }

        /**
         * Draws the triangle as this frame's painting
         */
        @Override
        public void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D) g;
            g2d.draw(triangle);
        }

        //Required methods for MouseListener, though the only one you care about is click
        public void mousePressed(MouseEvent e) {
        }

        public void mouseReleased(MouseEvent e) {
        }

        public void mouseEntered(MouseEvent e) {
        }

        public void mouseExited(MouseEvent e) {
        }

        /**
         * Called whenever the mouse clicks. Could be replaced with setting the
         * value of a JLabel, etc.
         */
        public void mouseClicked(MouseEvent e) {
            Graphics2D g2d = (Graphics2D) this.getGraphics();
            Point p = e.getPoint();
            if (triangle.contains(p)) {
                System.out.println("1");

                g2d.clearRect(0, 0, 1000, 1000);
                triangle.reset();
                g2d.setColor(Color.MAGENTA);
                triangle2 = new Polygon();
                triangle2.addPoint(600, 550);  // left
                triangle2.addPoint(700, 350); //top
                triangle2.addPoint(800, 550);  //right
                g2d.draw(triangle2);
            } else {
                System.out.println("Triangle dont have point");
            }
        }
    }
}

Answer 1

paint()和repaint()可以正常工作，但是由於要使用它們，因此您不使用它們。 窗口系統不會保留組件外觀的持久圖像。 它希望您的組件能夠按需重新繪制其整個外觀（例如，當調整窗口大小或最小化窗口時）。

如果使用getGraphics()捕獲Graphics對象並在組件上繪制某些東西，則當/當需要重新繪制整個組件時，繪制的內容確實會丟失。 因此，您不應這樣做，而應確保您的paintComponent方法具有完全重新繪制組件所需的所有信息。

---

如果一次只希望在屏幕上顯示一個三角形，則不要創建單獨的變量triangle2 。 只需按如下所示更改鼠標單擊處理程序來替換一個三角形即可：

public void mouseClicked(MouseEvent e) {
    Point p = e.getPoint();
    if (triangle.contains(p)) {
        triangle = new Polygon();
        triangle.addPoint(600, 550); // left
        triangle.addPoint(700, 350); //top
        triangle.addPoint(800, 550); //right
        repaint();
    } else {
        System.out.println("Point not in triangle");
    }
}

您的paintComponent方法應調用super.paintComponent以確保繪制背景，但否則無需更改它：

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D)g;
    g2d.draw(triangle);
}

或者，如果嘗試在屏幕上保留多個三角形，例如，每次單擊都添加一個新的三角形，則應將它們添加到形狀列表中，以便在需要重新粉刷組件時繪制該形狀：

private final List<Shape> shapes = new ArrayList<>();

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D)g;
    for (Shape s : shapes)
        g2d.draw(s);
}

然后，要控制屏幕上顯示的一組形狀，操縱列表的內容，並調用repaint(); 。

例如，要在屏幕上添加新形狀：

Polygon triangle = new Polygon();
triangle.addPoint(200, 300);
triangle.addPoint(200, 200);
triangle.addPoint(300, 200);
shapes.add(triangle);
repaint();

要從屏幕上刪除所有形狀：

shapes.clear();
repaint();

---

您還應確保在程序啟動時切換到Swing線程，因為從主線程與Swing組件進行交互並不安全。 在main ：

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            JFrame frame = new JFrame();
            .
            .
            .
            frame.setVisible(true);
        }
    });
}

Answer 2

您的mouseClicked方法不應創建新的Triangle對象。 重置triangle只需向其添加新點即可。 也不要使用此方法繪制，而是調用repaint ：

   public void mouseClicked(MouseEvent e) {
        Point p = e.getPoint();
        if (triangle.contains(p)) {
            System.out.println("1");
            triangle.reset();            // change the current triangle
            triangle.addPoint(600, 550); // new left
            triangle.addPoint(700, 350); // new top
            triangle.addPoint(800, 550); // new right
            repaint();                   // force repainting
        } else {
            System.out.println("Triangle dont have point");
        }
    }

現在，如果您想要許多三角形，則應該有一個Polygon的集合。 像這樣 ：

public static class TrianglePanel extends JPanel implements MouseListener {
    private Vector<Polygon> triangles;

    public TrianglePanel() {
        n = 0;
        // Create an empty collection
        triangles = new Vector<Polygon>();

        //Create first triangle
        Polygon triangle = new Polygon();
        triangle.addPoint(400, 550); //left   
        triangle.addPoint(600, 550); //right
        triangle.addPoint(500, 350); //top

        // Add the triangle to the collection
        triangles.add(triangle);

        //Add mouse Listener
        addMouseListener(this);

        //Set size to make sure that the whole triangle is shown
        setPreferredSize(new Dimension(300, 300));
    }

    /**
     * Draws the triangles as this frame's painting
     */
    @Override
    public void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        for (Polygon p : triangles) // Draw all triangles in the collection
            g2d.draw(p);
    }

    //Required methods for MouseListener, though the only one you care about is click
    public void mousePressed(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}

    /**
     * Called whenever the mouse clicks. Could be replaced with setting the
     * value of a JLabel, etc.
     */
    public void mouseClicked(MouseEvent e) {
        Graphics2D g2d = (Graphics2D) this.getGraphics();
        Point p = e.getPoint();
        // Do what you want with p and the collection
        // For example : remove all triangles that contain the point p
        ListIterator<Polygon> li = triangles.listIterator();
        while (li.hasNext()) {
            if (li.next().contains℗) li.remove();
        }
        // Do what you want to update the list
        // For example: Add a new triangle...
        Polygon triangle = new Polygon();
        triangle.addPoint(600+n, 550);  // left
        triangle.addPoint(700+n, 350);  //top
        triangle.addPoint(800+n, 550);  //right
        triangles.add(triangle); // add the new triangle to the list
        n += 10; // next new triangle will be "moved" right
        repaint();
    }
    private int n;
}