如何让JPanel在这个例子中变得透明?渐变背景不可见:
package test;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.BoxLayout;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JWindow;
public class PaintJPanelOnJWindow extends JWindow {
public PaintJPanelOnJWindow() {
JPanel panel = new JPanel();
panel.setPreferredSize(new Dimension(350, 120));
panel.setMinimumSize(new Dimension(350, 120));
panel.setMaximumSize(new Dimension(350, 120));
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
panel.setOpaque(false);
JLabel someText = new JLabel("I'm not transparent and my JPanel too :(");
someText.setOpaque(false);
panel.add(someText);
add(panel);
pack();
setLocationRelativeTo(null);
setVisible(true);
}
@Override
public void paint(Graphics g) {
Graphics2D g2d = (Graphics2D) g.create();
try {
int w = getWidth(), h = getHeight();
g2d.setPaint(new GradientPaint(0, 0, Color.RED, 0, h, Color.WHITE));
g2d.fillRect(0, 0, w, h);
} finally {
g2d.dispose();
}
super.paint(g);
}
}
最佳答案
当前的问题是
super.paint(g);
在 paint
方法中的自定义绘制代码之后被调用,这将导致任何先前的绘制丢失。调用 panel.setOpaque(false)
不会影响 paint
方法中所做的操作。无需为问题中的任何组件调用 setOpaque
- 默认情况下,正确实现自定义绘制时会显示背景。
这应该通过覆盖 paintComponent 来完成方法。这意味着创建一个新的 JPanel
并将自定义绘画功能放置在其中,而不是放置在 JWindow
等顶级容器中。
示例:
public class PaintJPanelApp {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame("Gradient App");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setUndecorated(true);
frame.setLocationRelativeTo(null);
JLabel someText = new JLabel("I AM transparent and my JPanel too :)");
GradientPanel gradientPanel = new GradientPanel();
gradientPanel.add(someText);
frame.add(gradientPanel);
frame.pack();
frame.setVisible(true);
}
});
}
static class GradientPanel extends JPanel {
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
int w = getWidth();
int h = getHeight();
Graphics2D g2d = (Graphics2D) g;
g2d.setPaint(new GradientPaint(0, 0, Color.RED, 0, h, Color.WHITE));
g2d.fillRect(0, 0, w, h);
}
}
}
关于java - 如果 `set setOpaque(false);`,JWindow 上的 JPanel 不透明 - 为什么?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18262624/