Repaint() 方法不会一一调用 paint() 和 paintComponent() 方法，只有 paintComponent() 方法有效

Question

我的应用程序可以裁剪图像。我想要实现的是在根据从 MouseListeners 获取的坐标切割图像之前绘制矩形。这是我的代码：

public class ImageScreenShot extends JPanel implements MouseListener, MouseMotionListener {

    ImagePanel im;

    int drag_status = 0, c1, c2, c3, c4;

    public int getC1() {
        return c1;
    }

    public int getC2() {
        return c2;
    }

    public int getC3() {
        return c3;
    }

    public int getC4() {
        return c4;
    }

    public void cut() {
        im = new ImagePanel();
        GraphicalUserInterface.getFrame().add(im);
        im.addMouseMotionListener(this);
        im.addMouseListener(this);
    }

    public void draggedScreen() throws Exception {
        int w = c1 - c3;
        int h = c2 - c4;
        w = w * -1;
        h = h * -1;
        Robot robot = new Robot();
        BufferedImage img = robot.createScreenCapture(new Rectangle(c1, c2, w, h));
        File save_path = new File("screen1.jpg");
        ImageIO.write(img, "JPG", save_path);
        GraphicalUserInterface.getLabelIcon().setIcon(new ImageIcon(new ImageIcon(img).getImage().getScaledInstance(img.getWidth(),img.getHeight(),Image.SCALE_SMOOTH)));
        JOptionPane.showConfirmDialog(null,"Would you like to save your cropped Pic?");
        if(JOptionPane.YES_OPTION == 0){
            PicChanges.getCurrentLabel();
        } else {
            PicChanges.getCurrentLabel();

        }
        System.out.println("Cropped image saved successfully.");
    }

    @Override
    public void mouseClicked(MouseEvent arg0) {
    }

    @Override
    public void mouseEntered(MouseEvent arg0) {
    }

    @Override
    public void mouseExited(MouseEvent arg0) {
    }

    @Override
    public void mousePressed(MouseEvent arg0) {
        repaint();
        c1 = arg0.getXOnScreen();
        c2 = arg0.getYOnScreen();
    }

    @Override
    public void mouseReleased(MouseEvent arg0) {
        repaint();
        if (drag_status == 1) {
            c3 = arg0.getXOnScreen();
            c4 = arg0.getYOnScreen();
            try {
                this.repaint();
                draggedScreen();
            } catch (Exception e) {
                e.printStackTrace();
            }
        } else {
            System.out.println("Issue is under construction");
        }
    }

    @Override
    public void mouseDragged(MouseEvent arg0) {
        repaint();
        drag_status = 1;
        c3 = arg0.getXOnScreen();
        c4 = arg0.getYOnScreen();
    }

    @Override
    public void mouseMoved(MouseEvent arg0) {
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        int w = c1 - c3;
        int h = c2 - c4;
        w = w * -1;
        h = h * -1;
        if (w < 0)
            w = w * -1;
        g.setColor(Color.RED);
        g.drawRect(c1, c2, w, h);
        System.out.println("paint component");

    }
}

public class ImagePanel extends JPanel {
    private BufferedImage imageToCut;

    public ImagePanel() {
        Dimension size = new 
        Dimension(GraphicalUserInterface.getLabelIcon().getSize());
        setPreferredSize(size);
        setMaximumSize(size);
        setMinimumSize(size);
        setSize(size);
    }

    @Override
    protected void paintComponent(Graphics g) {
        g.drawImage(imageToCut, 0, 0, null);
        System.out.println("painted");
    }
}

我很困惑，因为我不知道如何调用 paint() 方法，这就是为什么到目前为止，图像已正确裁剪但未绘制矩形。据我所知，我的 paintComponent() 方法在我调用 ImagePanel class 并在调用 repaint() 方法的地方添加 MouseListeners 时起作用。

要调用 paint() 方法，我需要调用 ImageScreenShot class 但这里出现了问题。

所以我的问题是如何在ImageScreenShot的MouseListeners中调用repaint()方法调用的paint()方法class?

Answer 1

使用 arg0.getComponent().repaint();，其中 arg0 是 MouseEvent。它将重新绘制触发事件的组件。参见 https://docs.oracle.com/javase/8/docs/api/java/awt/event/ComponentEvent.html#getComponent--

Returns: the Component object that originated the event, or null if the object is not a Component.

Answer 2

我没有测试过你的代码，但乍一看我可以看出：

您正在扩展 JPanel，没问题，但是您正在覆盖 paint(...) 方法，您不应该这样做，您需要覆盖 paintComponent(...)
在你的第二个 class 上你覆盖了 paintComponent(...) 但你没有调用
```
super.paintComponent(g);
```
其中，打破了油漆链。并且可能（连同第一点）是您错误的原因。
请参阅 Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?（是），您需要覆盖 getPreferredSize() 并在您的应用程序中调用 pack()。

Repaint() 方法不会一一调用 paint() 和 paintComponent() 方法，只有 paintComponent() 方法有效

Repaint() method doesn't invoke paint() & paintComponent() methods one by one, only paintComponent () method is working

java

swing

repaint