java - 创建带有渐变的 JLabel

Question

我是 Java 的新手，我正在尝试使用 JLabel 创建一个标题，并将其填充为渐变。我无法让它工作，我已经尝试了一段时间。我一直在从这里和其他网站上获取一些信息，但似乎无法完成这项工作，也无法理解其他人更复杂的代码是否有效。到目前为止，这是我的两个类(class):

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EtchedBorder;
public class Test {
    public static void main(String[] args) {
        new Test().setupGUI();
    }
    public void setupGUI() {
        //set up frames and buttons etc.
            JFrame theFrame = new JFrame ("Crystal Ball");
            theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            JPanel background = new JPanel();
            background.setBackground(Color.BLUE);
            background.setLayout(new BoxLayout(background, BoxLayout.PAGE_AXIS));
            theFrame.setSize(500,1000);
            DLabel heading = new DLabel("Guess a Number");
            heading.setText("GUESS A NUMBER");
            heading.setPreferredSize(new Dimension(theFrame.getWidth(),100));
            heading.setFont(new Font("Serif", Font.PLAIN, 40));
            heading.setAlignmentX(Component.CENTER_ALIGNMENT);
            //heading.setBackground(Color.YELLOW);
            heading.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.RAISED));
            background.add(heading);
            theFrame.getContentPane().add(background);
            theFrame.pack();
            theFrame.setVisible(true);
            //startGame();
        }
}

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.BorderFactory;
import javax.swing.JLabel;

public class DLabel extends JLabel
{

    Dimension size = new Dimension(70, 80);

    public DLabel(String name)
    {
        this.setPreferredSize(size);
        this.setText(name);
        this.setBorder(BorderFactory.createBevelBorder(TOP, Color.white, Color.black));
        this.setOpaque(true);
    }

    public void paintComponent(Graphics g) {
      // super.paintComponent(g);  // *** commented
      Graphics2D g2d = (Graphics2D) g;
      Color color1 = Color.YELLOW;
      Color color2 = color1.brighter();
      int w = getWidth();
      int h = getHeight();
      GradientPaint gp = new GradientPaint(0, 0, color1, 0, h, color2);
      g2d.setPaint(gp);
      g2d.fillRect(0, 0, w, h);
      super.paintComponent(g); // *** added
    }

}

Answer 1

您实际上可以做一个小“技巧”​​，通过让标签保持透明，您实际上可以在调用 super.paintComponent 之前在文本下方进行绘画，例如...

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.LinearGradientPaint;
import java.awt.Point;
import java.awt.Rectangle;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestLabel101 {

    public static void main(String[] args) {
        new TestLabel101();
    }

    public TestLabel101() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JLabel {

        public TestPane() {
            setText("Happy, Happy");
            setForeground(Color.WHITE);
            setHorizontalAlignment(CENTER);
        }

        @Override
        protected void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D) g.create();
            LinearGradientPaint lgp = new LinearGradientPaint(
                    new Point(0, 0), 
                    new Point(0, getHeight()), 
                    new float[]{0.142f, 0.284f, 0.426f, 0.568f, 0.71f, 0.852f, 1f}, 
                    new Color[]{Color.PINK, Color.MAGENTA, Color.BLUE, Color.GREEN, Color.YELLOW, Color.ORANGE, Color.RED});
            g2d.setPaint(lgp);
            g2d.fill(new Rectangle(0, 0, getWidth(), getHeight()));
            g2d.dispose();
            super.paintComponent(g);
        }

    }

}

nb:我应该指出这个过程是低效的，因为 RepaintManager 仍然想要在组件下绘制

还有一个窍门，但我两岁的女儿想看看圣诞老人是否在这里 ;)

已更新

另一个技巧涉及了解绘画过程的实际工作原理。当你调用super.paintComponent时，它会调用ComponentUI上的update方法(look and feel delegate)，这实际上就是填充的方法背景 如果组件是不透明的，则此方法会调用外观委托(delegate)的 paint 方法，该方法实际上会进行基础绘制...

我们可以稍微绕过这个过程，而不是调用 super.paintComponent，我们可以直接调用外观委托(delegate)的 paint 方法...

public class TestPane extends JLabel {

    public TestPane() {
        setText("Happy, Happy");
        setForeground(Color.WHITE);
        setHorizontalAlignment(CENTER);
        setOpaque(true);
    }

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g.create();
        LinearGradientPaint lgp = new LinearGradientPaint(
                new Point(0, 0), 
                new Point(0, getHeight()), 
                new float[]{0.142f, 0.284f, 0.426f, 0.568f, 0.71f, 0.852f, 1f}, 
                new Color[]{Color.PINK, Color.MAGENTA, Color.BLUE, Color.GREEN, Color.YELLOW, Color.ORANGE, Color.RED});
        g2d.setPaint(lgp);
        g2d.fill(new Rectangle(0, 0, getWidth(), getHeight()));
        g2d.dispose();
        getUI().paint(g, this);
    }

}

这比前面的示例更有效，因为它不需要 RepaintManager 来绘制此组件下方的区域，但它可能不适用于所有外观