java - repaint() 未在 Java 程序中调用

Question

我有一个简单的程序(其中大部分将用于其他用途)，它只在用户单击 drawPanel JPanel 并显示椭圆时绘制椭圆。问题是 repaint() 方法没有调用 paintComponent()。这是为什么？

代码如下:

// Imports Used:
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import javax.swing.*;
import java.awt.geom.*;
// Class DrawPolygon
public class DrawPolygon extends JPanel implements MouseListener
{
// Variables used in GUI
static JFrame frame;
static JPanel drawPanel;
static JPanel labelPanel;
static JPanel primaryPanel;
static JButton loadButton;
static JButton saveButton;
static JButton clearButton;
static JButton addButton;
static JButton moveButton;
static JButton exitButton;
// Variables used for GUI interaction
static final int SIZE = 6;
static int numVertices;
ArrayList<Point> vertices;
static Color outlineColor = Color.RED;
static int lineWidth = 10;
static Color fillColor = Color.BLACK;
// Constructor for new Polygon Drawing Application
public DrawPolygon()
{
    // Create Frame
    frame = new JFrame("Vector Painter");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    // Set Location of GUI on screen
    frame.setLocation(225,100);
    // Primary Panel to store Draw Panel and Lable/Button Panel
    primaryPanel = new JPanel();
    // Create Label Panel
    createLabelPanel();
    // Create Draw Panel
    createDrawPanel();
    // Add panels to Primary
    primaryPanel.add(labelPanel);
    primaryPanel.add(drawPanel);
    // Add to frame
    frame.getContentPane().add(primaryPanel);
    frame.pack();
    frame.setVisible(true);
}
// Add Buttons to left side
public void createLabelPanel()
{
    // Label Panel to add Buttons
    labelPanel = new JPanel();
    labelPanel.setBackground(Color.BLACK);
    labelPanel.setPreferredSize(new Dimension(200,600));
    // Create JButtons
    loadButton = new JButton("LOAD");
    loadButton.setPreferredSize(new Dimension(180,75));
    loadButton.setBackground(Color.BLACK);
    loadButton.setForeground(Color.WHITE);
    loadButton.addMouseListener(this);
    saveButton = new JButton("SAVE");
    saveButton.setPreferredSize(new Dimension(180,75));
    saveButton.setBackground(Color.BLACK);
    saveButton.setForeground(Color.WHITE);
    saveButton.addMouseListener(this);
    clearButton = new JButton("CLEAR");
    clearButton.setPreferredSize(new Dimension(180,75));
    clearButton.setBackground(Color.BLACK);
    clearButton.setForeground(Color.WHITE);
    clearButton.addMouseListener(this);
    addButton = new JButton("ADD");
    addButton.setPreferredSize(new Dimension(180,75));
    addButton.setBackground(Color.BLACK);
    addButton.setForeground(Color.WHITE);
    addButton.addMouseListener(this);
    moveButton = new JButton("MOVE");
    moveButton.setPreferredSize(new Dimension(180,75));
    moveButton.setBackground(Color.BLACK);
    moveButton.setForeground(Color.WHITE);
    moveButton.addMouseListener(this);
    exitButton = new JButton("EXIT");
    exitButton.setPreferredSize(new Dimension(180,75));
    exitButton.setBackground(Color.BLACK);
    exitButton.setForeground(Color.WHITE);
    exitButton.addMouseListener(this);
    // Add Buttons to Label Panel
    labelPanel.add(loadButton);
    labelPanel.add(saveButton);
    labelPanel.add(clearButton);
    labelPanel.add(addButton);
    labelPanel.add(moveButton);
    labelPanel.add(exitButton);
}
// Creates Draw Panel
public void createDrawPanel()
{
    // Draw Panel to Draw Polygons
    drawPanel = new JPanel();
    drawPanel.setBackground(Color.BLACK);
    drawPanel.setPreferredSize(new Dimension(600,600));
    drawPanel.addMouseListener(this);
    vertices = new ArrayList<>();
}

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

    g.setColor(Color.ORANGE);

    for (Point spot : vertices)
    {
        g.fillOval(spot.x-SIZE, spot.y-SIZE, SIZE*2, SIZE*2);
    }

    g.drawString("Count: " + vertices.size(), 5, 15);

    System.out.println("repaint is working?");
}

// Execute when Load button is clicked
public void loadButton()
{
    System.out.println("Load Button CLICKED!!");
}
// Execute when Save button is clicked
public void saveButton()
{
    System.out.println("Save Button CLICKED!!");
}
// Execute when Clear button is clicked
public void clearButton()
{
    System.out.println("Clear Button CLICKED!!");
}
// Execute when Add button is clicked
public void addButton()
{
    System.out.println("Add Button CLICKED!!");
}
// Execute when Move button is clicked
public void moveButton()
{
    System.out.println("Move Button CLICKED!!");
}
public void mouseClicked(MouseEvent e)
{
    if (e.getSource() == loadButton)
    {
        loadButton();
    }
    else if (e.getSource() == saveButton)
    {
        saveButton();
    }
    else if (e.getSource() == clearButton)
    {
        clearButton();
    }
    else if (e.getSource() == addButton)
    {
        addButton();
    }
    else if (e.getSource() == moveButton)
    {
        moveButton();
    }
    else if (e.getSource() == exitButton)
    {
        System.exit(0);
    }
    else if (e.getSource() == drawPanel)
    {
        System.out.println("TEST");
        vertices.add(e.getPoint());
        repaint();
    }
}
// These are here because program wouldn't compile without them
public void mousePressed(MouseEvent e){}
public void mouseReleased(MouseEvent e){}
public void mouseExited(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
// Main Function
public static void main(String[] args) 
{
    // Create Frame
    new DrawPolygon();        
}
}

Answer 1

实际上正在调用重绘，但是在当前的 DrawPolygon 对象上，但是由于您似乎没有显示其中一个 paintComponent(...) 永远不会被调用。澄清一下，您当前的类 DrawPolygon 扩展了 JPanel，但它似乎并未添加到作为 GUI 层次结构一部分的任何容器中。也许您想将当前对象(this)添加到 GUI 的某处？事实上，您可能应该考虑使用当前对象代替 drawPanel JPanel 对象。我会考虑完全删除该变量。

同样与您的问题无关的是，您几乎不想在应该使用 ActionListeners 的 JButtons 上使用 MouseListeners。