矩形绘制java Swing GUI的问题

Question

我正在用java编写一个程序，该程序根据鼠标坐标在屏幕上绘制一个矩形。但是，我很难为这个矩形找到正确的颜色。目标是在用户点击屏幕并选择颜色后，绘制一个具有正确颜色的矩形。我尝试过案例场景，但无法正常工作。对不工作的零件进行了注释。

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

public class test extends JFrame implements ActionListener, MouseListener, KeyListener {
    Shape box = new Rectangle2D.Float(10, 10, 10, 10);
    public test () {
        setSize(250,150);
        addMouseListener(this);
        addKeyListener(this);
        Color bgColor = new Color(125,125,125);
        setBackground(bgColor);
    }
    public static void main(String[] args) {
        java.awt.EventQueue.invokeLater(new Runnable() {
              public void run() {
                   test frame = new test();
                   frame.setVisible(true);
              }
        });
    }
    public void actionPerformed(ActionEvent ae) {
    }
    public void drawRectangle(int x, int y) {
        Graphics g = this.getGraphics();
        // KeyEvent e = this.getKeyChar();
        // switch (test.keyTyped()) {
        // case b: 
            g.drawRect(x, y, x, y);
            g.setColor(Color.BLUE);
            g.fillRect(x, y, 2, 2);
        // case r:
            // g.drawRect(x, y, x, y);
            // g.setColor(Color.RED);
            // g.fillRect(x, y, 2, 2);
        // case y:
            // g.drawRect(x, y, x, y);
            // g.setColor(Color.Yellow);
            // g.fillRect(x, y, 2, 2);
        // case g:
            // g.drawRect(x, y, x, y);
            // g.setColor(Color.GREEN);
            // g.fillRect(x, y, 2, 2);
            //}
    }
    int x, y;
    public void mouseClicked(MouseEvent e) {
        x = e.getX();
        y = e.getY();
        repaint();
    }
    public void keyTyped(KeyEvent e) {
        char c = e.getKeyChar();
        c = Character.toLowerCase(c);   
    }
    @Override
    public void paint(Graphics g) {
        g.setColor(Color.white);
        g.drawString("Click anywhere to draw a rectangle", 50, 250);
        g.drawString("Choose color by pressing the corresponding key on your keyboard: ", 50, 270);
        g.setColor(Color.blue);
        g.drawString("B: Blue ", 50, 285);
        g.setColor(Color.red);
        g.drawString("R: Red ", 95, 285);
        g.setColor(Color.yellow);
        g.drawString("Y: Yellow ", 140, 285);
        g.setColor(Color.green);
        g.drawString("G: Green ", 195, 285);

        drawRectangle(x, y);
    }
    public void mouseExited(MouseEvent e) {
        // TODO Auto-generated method stub
    }
    public void mousePressed(MouseEvent e) {
        // TODO Auto-generated method stub
    }
    public void mouseReleased(MouseEvent e) {
        // TODO Auto-generated method stub
    }
    public void mouseEntered(MouseEvent e) {
        // TODO Auto-generated method stub
    }
    public void keyPressed(KeyEvent e) {
        // TODO Auto-generated method stub  
    }
    public void keyReleased(KeyEvent e) {
        // TODO Auto-generated method stub      
    }   
}

Answer 1

您可以这样做：

HashMap<Integer, Color> colorsMap = new HashMap<>();
int selectedColor = Color.BLUE;
public test() {
    ....
    colorsMap.put(KeyEvent.VK_B, Color.BLUE);
    colorsMap.put(KeyEvent.VK_R, Color.RED);
    colorsMap.put(KeyEvent.VK_Y, Color.YELLOW);
    colorsMap.put(KeyEvent.VK_G, Color.GREEN);
    ....
}
public void drawRectangle(Graphics g, int x, int y) {
    g.setColor(selectedColor);
    g.fillRect(x, y, 2, 2);
}
@Override
public void paint(Graphics g) {
    ....
    drawRectangle(g, x, y);
    ....
}
public void keyPressed(KeyEvent e) {
    if(colorsMap.containsKey(e.getKeyCode())){
        selectedColor = colorsMap.get(e.getKeyCode());
    }
}

Answer 2

您正在对图形颜色状态的颜色进行硬编码：

g.setColor(Color.BLUE);

因此，无论用户选择什么，它都将保持蓝色，这一点也不奇怪。

建议：

• 不要硬编码，而是在这一行中使用Color变量，并在用户选择颜色时设置变量的状态
• 所以给你的类一个颜色字段，比如说rectangleColor
• 在获得用户输入的方法中，设置该字段的值，然后调用repaint()
• 不要在paint方法中绘制，而是在JPanel的paintComponent方法中绘制
• 不要使用getGraphics()来获取Graphics对象，而是使用JVM提供的Graphics对象在paintComponent方法中进行绘制
• 不要忘记调用超级绘制方法，例如paintComponent方法覆盖中的super.paintComponent(g)。这将允许JPanel进行房屋维护绘画