所以,你的主要问题是:
setBackground(new Color(0, 0, 0, 0));
Swing只知道如何绘制完全透明或完全不透明的组件,这是通过
opaque
所有物通过提供基于alpha的颜色,Swing不会知道,当由于某种原因更新组件时,它会绘制该组件下面出现的组件
相反,您应该使用
setOpaque
并通过它
false
InnerPanel
import java.awt.Color;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class InnerPanel extends JPanel {
public InnerPanel() {
setOpaque(false);
setBackground(Color.RED);
JLabel label = new JLabel("testing");
add(label);
}
}
MainPanel
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import javax.swing.JPanel;
public class MainPanel extends JPanel {
private InnerPanel panel;
public MainPanel() {
setLayout(new BorderLayout());
panel = new InnerPanel();
add(panel, BorderLayout.CENTER);
}
@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 = Color.RED;
Color color2 = Color.GREEN;
GradientPaint gp = new GradientPaint(0, 0, color1, 0, h, color2);
g2d.setPaint(gp);
g2d.fillRect(0, 0, w, h);
}
}
GuiApp
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class GuiApp {
public static void main(String[] args) {
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 MainPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
}
当它们放在一起时。。。