Question

我无法将下面链接的代码完全按照我的意愿去做。

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

public class Gui {

    static JFrame frame;
    static JLabel label;

    public static void main (String[] args) {
        Gui gui = new Gui();
        gui.go();
    }

    public void go () {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400,300);
        frame.setVisible(true);

        MyDrawPanel panel = new MyDrawPanel();
        frame.getContentPane().add(BorderLayout.CENTER, panel);

        label = new JLabel("I'm a label");
        frame.getContentPane().add(BorderLayout.WEST, label);

        JButton colorButton = new JButton("Change Colors");
        ColorButtonListener colorButtonListener = new ColorButtonListener();
        colorButton.addActionListener(colorButtonListener); 
        frame.getContentPane().add(BorderLayout.SOUTH, colorButton);

        JButton labelButton = new JButton("Change Label");
        LabelButtonListener labelButtonListener = new LabelButtonListener();
        labelButton.addActionListener(labelButtonListener); 
        frame.getContentPane().add(BorderLayout.EAST, labelButton);
    }
}

class ColorButtonListener implements ActionListener {
    JFrame frame = Gui.frame;
    public void actionPerformed (ActionEvent event) {
        frame.repaint();
    }
}

class LabelButtonListener implements ActionListener {
    JLabel label = Gui.label;
    public void actionPerformed (ActionEvent event) {
        if (label.getText() == "That hurt") {
            label.setText("I'm a label");
        } else {
            label.setText("That hurt");
        }
    }
}

class MyDrawPanel extends JPanel {
    public void paintComponent (Graphics g) {
        Graphics2D g2d = (Graphics2D) g;

        int red = (int) (Math.random() * 256);
        int green = (int) (Math.random() * 256);
        int blue = (int) (Math.random() * 256);
        Color startColor = new Color(red, green, blue);

        red = (int) (Math.random() * 256);
        green = (int) (Math.random() * 256);
        blue = (int) (Math.random() * 256);
        Color endColor = new Color(red, green, blue);

        GradientPaint gradient = new GradientPaint(70, 70, startColor, 150, 150, endColor);
        g2d.setPaint(gradient);
        g2d.fillOval(0, 0, this.getWidth(), this.getHeight());

    }
}

有一个用于绘制圆的面板类，然后面板位于框架的中心区域。

标签位于框架的西部区域，两个按钮colorButton（位于南侧）和labelButton（位于东侧）应分别控制圆圈和标签。 2个类ColorButtonListener和LabelButtonListener实现ActionListener接口，并分别使用colorButton和labelButton注册。单击时的颜色按钮应绘制一个随机颜色的圆圈，单击时标签按钮应在文本“我是一个标签”和“那个受伤”之间切换。

现在，我遇到的问题是标签按钮。单击它时，它不仅会更改文本（按预期方式），还会重绘圆圈。此按钮不应重绘圆圈。颜色按钮按预期工作。

Answer 1

这是因为如果新文本与旧文本不同，setText()方法会在内部调用repaint()。因此，无论何时单击该按钮都会导致颜色发生变化。

Answer 2

问题是您无法控制何时可能发生重绘。每次调用paintComponent时都无法更改颜色，而无法控制，只有当您想要并在paintComponent方法中引用时才更改颜色，例如

class MyDrawPanel extends JPanel {
    private Color startColor;
    private Color endColor;

    // And setters or some other way
    // to randomise the colors

    public void paintComponent (Graphics g) {
        Graphics2D g2d = (Graphics2D) g;

        GradientPaint gradient = new GradientPaint(70, 70, startColor, 150, 150, endColor);
        g2d.setPaint(gradient);
        g2d.fillOval(0, 0, this.getWidth(), this.getHeight());

    }
}

查看Painting in AWT and Swing了解详情

Java中的事件处理无法按预期工作

2 个答案: