Question

它运行，按钮工作，但我不能用paint（）绘制它。我认为它与SwingDraw上的main方法有关，但我并非100％肯定。感谢您的帮助，并为长代码感到抱歉：/

SwingDraw：

// Import Core Java packages
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.*;
import javax.swing.*;

public class SwingDraw extends JFrame implements ActionListener, ItemListener{

// Initial Frame size
static final int WIDTH = 1500;                // frame width
static final int HEIGHT = 1000;               // frame height

// Color choices
static final String[] COLOR_NAMES = new String[]{"None", "Red", "Blue", "Green"};
static final Color COLORS[] = {null, Color.red, Color.blue, Color.green }; 

// Button control
JButton circle;
JButton roundRec;
JButton threeDRec;
JButton line;
JButton square;
JButton oval;

JButton clear;
JButton delete;

// List to keep track of shapes
JList<String> shapesKeeper;

// Color choice box
JComboBox<String> colorChoice = new JComboBox<>(COLOR_NAMES);

SwingDrawCanvas betterCanvas = new SwingDrawCanvas();

/**
 * Constructor
 */
public SwingDraw() {
    // Create a frame
    setSize(WIDTH, HEIGHT);
    setLocation(130, 100);
    // add window closing listener
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


    // create panel for controls
    JPanel topPanel = new JPanel();
    JPanel leftList = new JPanel();



    // create button control 
    JPanel buttonPanel = new JPanel(); 
    topPanel.add(buttonPanel, BorderLayout.NORTH);

    circle = new JButton("Circle");
    buttonPanel.add(circle);
    roundRec = new JButton("Rounded Rectangle");
    buttonPanel.add(roundRec);
    threeDRec = new JButton("3D Rectangle");
    buttonPanel.add(threeDRec);
    line = new JButton("Line");
    buttonPanel.add(line);
    square = new JButton("Square");
    buttonPanel.add(square);
    oval = new JButton("Oval");
    buttonPanel.add(oval);
    clear = new JButton("Clear");
    buttonPanel.add(clear);

    JPanel listPanel = new JPanel();
    leftList.add(listPanel, BorderLayout.WEST);
    JList<String> shapesKeeper = new JList<>();
    listPanel.add(shapesKeeper);
    delete = new JButton("Delete Shape");
    listPanel.add(delete);

    // add button listener
    circle.addActionListener(this);
    roundRec.addActionListener(this);
    threeDRec.addActionListener(this);
    line.addActionListener(this);
    square.addActionListener(this);
    oval.addActionListener(this);
    clear.addActionListener(this);

    // create panel for color choices
    JPanel colorPanel = new JPanel();
    JLabel label = new JLabel("Filled Color:");
    topPanel.add(colorPanel);
    colorPanel.add(label);
    JComboBox<String> colorChoice = new JComboBox<>(COLOR_NAMES);
    colorPanel.add(colorChoice);

    colorChoice.addItemListener(this);

    add(topPanel, BorderLayout.NORTH);
    add(leftList, BorderLayout.WEST);
    setVisible(true);

} // end of constructor


/**
 *  Implementing ActionListener
 */
public void actionPerformed(ActionEvent event) {
    if(event.getSource() == circle) {  // circle button
        betterCanvas.setShape(SwingDrawCanvas.CIRCLE);
    }
    else if(event.getSource() == roundRec) {  // rounded rectangle button
        betterCanvas.setShape(SwingDrawCanvas.ROUNDED_RECTANGLE);
    }
    else if(event.getSource() == threeDRec) { // 3D rectangle button
        betterCanvas.setShape(SwingDrawCanvas.RECTANGLE_3D);
    }
    else if(event.getSource() == clear){
        betterCanvas.setShape(SwingDrawCanvas.CLEAR);
    }
    else if(event.getSource() == line){
        betterCanvas.setShape(SwingDrawCanvas.LINE);
    }
    else if(event.getSource() == square){
        betterCanvas.setShape(SwingDrawCanvas.SQUARE);
    }
    else if(event.getSource() == oval){
        betterCanvas.setShape(SwingDrawCanvas.OVAL);

    }
}

/**
 * Implementing ItemListener
 */
public void itemStateChanged(ItemEvent event) {
    Color color = COLORS[colorChoice.getSelectedIndex()];
    betterCanvas.setFilledColor(color);
}

/**
 * the main method
 */
public static void main(String[] argv) {
    new SwingDraw();
}
}

SwingDrawCanvas：

public class SwingDrawCanvas extends JPanel implements MouseListener, MouseMotionListener {

// Constants for shapes
public static final int CIRCLE = 1;
public static final int ROUNDED_RECTANGLE = 2;
public static final int RECTANGLE_3D = 3;
public static final int LINE = 4;
public static final int SQUARE = 5;
public static final int OVAL = 6;

public static final int CLEAR = 7;

// Coordinates of points to draw
private int x1, y1, x2, y2;

// shape to draw
private int shape = CIRCLE;
/**
 * Method to set the shape
 */
public void setShape(int thisShape) {
    System.out.println("HEY");
    this.shape = thisShape;
    System.out.println(shape);
}

// filled color
private Color filledColor = null;
/**
 * Method to set filled color
 */
public void setFilledColor(Color color) {
    filledColor = color;
}

/**
 * Constructor
 */
public SwingDrawCanvas() {
    addMouseListener(this);
    addMouseMotionListener(this);
} // end of constructor

/**
 * painting the component
 */
public void paint(Graphics g) {

    System.out.println("ARHFHASJDASHDHAs");
    super.paint(g);

    System.out.println("AHAHAHAHAHAHAHA");

    g.drawString("FUCK", 1, 1);

    // the drawing area
    int x, y, width, height;

    // determine the upper-left corner of bounding rectangle
    x = Math.min(x1, x2);
    y = Math.min(y1, y2);

    // determine the width and height of bounding rectangle
    width = Math.abs(x1 - x2);
    height = Math.abs(y1 - y2);


    if(filledColor != null)
        g.setColor(filledColor);
    switch (shape) {
        case ROUNDED_RECTANGLE :
            if(filledColor == null)
                g.drawRoundRect(x, y, width, height, width/4, height/4);
            else
                g.fillRoundRect(x, y, width, height, width/4, height/4);
            break;
        case CIRCLE :
            int diameter = Math.max(width, height); 
            if(filledColor == null)
                System.out.println("HRE BITCHS");
            else
                System.out.println("HEY FUCK YOU GUY");
            break;
        case RECTANGLE_3D :
            if(filledColor == null)
                g.draw3DRect(x, y, width, height, true);
            else
                g.fill3DRect(x, y, width, height, true);
            break;
    }
}

/**
 * Implementing MouseListener
 */
public void mousePressed(MouseEvent event) {
    x1 = event.getX();
    y1 = event.getY();
}

public void mouseReleased(MouseEvent event) {
    x2 = event.getX();
    y2 = event.getY();
    repaint();
}

public void mouseClicked(MouseEvent e) {}
public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}

/**
 * Implementing MouseMotionListener
 */
public void mouseDragged(MouseEvent event) {
    x2 = event.getX();
    y2 = event.getY();
    repaint();
}

public void mouseMoved(MouseEvent e) {}

}

我不是很擅长这一点，我只是在找你们给我的任何帮助：D

Answer 1

您的函数应该是名称paint()，而不是paintComponent(Graphics g)。在创建paintComponent(Graphics g)函数时，您需要@Override以便java识别该函数，因为您无法直接调用paintComponent(Graphics g)。

此外，只要您想要刷新面板，就可以调用repaint()，也可以在编译代码后调整JFrame的大小。这两种方法都会调用paintComponent(Graphics g)函数。

为什么这段代码没有触发paint（）？

1 个答案: