如何在Jpanel区域内制作半透明的JPanel
我想制作一个半透明的JPanel ，我可以选择x坐标，y坐标，宽度和高度。 我发现一些材料制作了一个半透明的JPanel填充其父容器，但我不需要这种效果。 我需要一个半透明的JPanel其位置可以在父容器中指定，这样只有这个区域是半透明的，而父容器中的其他区域是不透明的。 我试过这段代码，但是不正确。 结果区域小于我想要的区域。 有什么问题，或者我怎么能得到这种效果？
public class TranslucentJPanel extends JPanel { private float transparency; public TranslucentJPanel(){ } /**set the transparency * * @param transparency:the transparency you want to set * * @return void */ public void setTransparent(float transparency) { this.transparency = transparency; } @Override protected void paintComponent(Graphics g){ super.paintComponent(g); Graphics2D graphics2d = (Graphics2D) g.create(); graphics2d.setComposite(AlphaComposite.SrcOver.derive(transparency)); graphics2d.fill(getBounds()); graphics2d.dispose(); } }
所以，立即想到两件事……
首先，不要使用getBounds ， Grapghics上下文已经转换为组件x / y位置，所以你加倍了。 相反，只需使用0x0并提供width和height ，如…
graphics2d.fillRect(0, 0, getWidth(), getHeight());
另外，请记住，大多数Swing组件默认是不透明的，这包括JList ， JScrollPane和它的JViewport ，如果你想让它们完全透视，你需要将它们设置为透明。
此外， JList使用的“默认”渲染器也将其自身渲染为不透明，因此如果您希望项目透明，则需要能够提供自己的渲染器…
import java.awt.AlphaComposite; import java.awt.BorderLayout; import java.awt.Component; import java.awt.Dimension; import java.awt.EventQueue; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.GridBagLayout; import java.awt.image.BufferedImage; import java.io.File; import java.io.IOException; import java.util.logging.Level; import java.util.logging.Logger; import javax.imageio.ImageIO; import javax.swing.DefaultListCellRenderer; import javax.swing.DefaultListModel; import javax.swing.JFrame; import javax.swing.JList; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; import javax.swing.border.EmptyBorder; public class Test { public static void main(String[] args) { new Test(); } public Test() { EventQueue.invokeLater(new Runnable() { @Override public void run() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { ex.printStackTrace(); } DefaultListModel model = new DefaultListModel<>(); model.addElement("Bananas"); model.addElement("Apples"); model.addElement("Pears"); model.addElement("Grapes"); model.addElement("Tim Tams"); JList list = new JList(model); list.setCellRenderer(new DefaultListCellRenderer() { @Override public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) { super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus); setOpaque(isSelected); return this; } }); list.setOpaque(false); JScrollPane sp = new JScrollPane(list); sp.setOpaque(false); sp.getViewport().setOpaque(false); TranslucentPane tp = new TranslucentPane(); tp.setLayout(new GridBagLayout()); tp.setLayout(new BorderLayout()); tp.add(sp); JFrame frame = new JFrame("Testing"); frame.setContentPane(new BackgroundPane()); frame.setLayout(new GridBagLayout()); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.add(tp); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } }); } public class TranslucentPane extends JPanel { private float alpha = 0.75f; public TranslucentPane() { setOpaque(false); setBorder(new EmptyBorder(5, 5, 5, 5)); } @Override public Dimension getPreferredSize() { return new Dimension(200, 200); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g.create(); g2d.setComposite(AlphaComposite.SrcOver.derive(alpha)); g2d.setColor(getBackground()); g2d.fillRect(0, 0, getWidth(), getHeight()); g2d.dispose(); } } public class BackgroundPane extends JPanel { private BufferedImage background; public BackgroundPane() { try { background = ImageIO.read(new File("C:\\Users\\shane\\Dropbox\\MegaTokyo\\thumnails\\megatokyo_omnibus_1_3_cover_by_fredrin-d4oupef.jpg")); } catch (IOException ex) { ex.printStackTrace(); } } @Override public Dimension getPreferredSize() { return new Dimension(background.getWidth(), background.getHeight()); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); int x = (getWidth() - background.getWidth()) / 2; int y = (getHeight() - background.getHeight()) / 2; g.drawImage(background, x, y, this); } } }