java - 如何使JPanel的背景渐变

Question

我想知道如何制作另一个 JPanel 中的背景渐变。在互联网上找到了许多文章，但它们都演示了如何覆盖 JPanel 的paintComponent()，而不是如何覆盖其中的 jPanel。
我使用 Netbeans IDE。我创建了一个新的 JPanel 类并且可以覆盖它的paintComponent()。我有另一个 jpanel（拖放到父 JPanel）。我想让它的背景渐变。

这是我为父母尝试的方法。有效。我怎样才能为孩子 jpanel 覆盖这个？

public void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        Color color1 = getBackground();
        Color color2 = color1.darker();
        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);
        }

Answer 1

如果你小心调用super.paintComponent(g)，你可以直接将渐变添加到面板中，如下所示。

为了可用性，我会抵制尝试使各个组件透明的诱惑。另请注意，不透明度由外观控制。

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
* @see http://stackoverflow.com/q/12220853/230513
*/
public class GradientPanel extends JPanel {

    private static final int N = 32;

    public GradientPanel() {
        this.setBorder(BorderFactory.createEmptyBorder(N, N, N, N));
        this.add(new JLabel("Test:", JLabel.CENTER));
        this.add(new JTextField("This is a test."));
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        Color color1 = getBackground();
        Color color2 = color1.darker();
        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);
    }

    private void display() {
        JFrame f = new JFrame("GradientPanel");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new GradientPanel().display();
            }
        });
    }
}

Answer 2

我想这就是你想要做的

jPanel1 = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                Graphics2D g2d = (Graphics2D) g;
                g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
                int w = getWidth();
                int h = getHeight();
                Color color1 = new Color(81,80,106);
                Color color2 = new Color(165,164,241);
                GradientPaint gp = new GradientPaint(0, 0, color1, 0, h, color2);
                g2d.setPaint(gp);
                g2d.fillRect(0, 0, w, h);
            }
        };