java - 想要一个带有透明背景图像的 JLabel

Question

我将此图标用于 JTable 的自定义呈现器中的 JLabel。选择表格中的行时，图标背景显示为白色。

我使用 paint.net 创建了一个绿色三角形，并将其背景设置为白色，alpha 值为 255。这就是我在这段代码中为 JLabel 创建 IconImage 所使用的图像；出于外部原因，我对图标使用了不同的宽度。这是一个示例程序，显示了已完成的工作:

package spacecheck.images;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.util.ArrayList;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

/**
 * represents an icon used in the directory tree; handles 'expanded' and
 * 'unexpanded' directories as well as indentation representing different
 * levels.
 * @author rcook
 *
 */
public class TreeIconExample
{
  public static int UNEXPANDED = 1;
  public static int EXPANDED = 2;

  @SuppressWarnings({"unused"})
  private void say (String msg) { System.out.println(msg); }

  private static ImageIcon expandedIcon = null;
  private static ImageIcon unexpandedIcon = null;
  private static int       iconHeight = 0;
  private static int       iconWidth  = 0;

  private static ArrayList<ImageIcon> cachedExpandedIcons = new ArrayList<ImageIcon>();
  private static ArrayList<ImageIcon> cachedUnexpandedIcons = new ArrayList<ImageIcon>();

  static
  {
    expandedIcon = new ImageIcon(TreeIconExample.class.getResource("images/Expanded.GIF"));
    unexpandedIcon = new ImageIcon(TreeIconExample.class.getResource("images/Unexpanded.GIF"));
    iconHeight = unexpandedIcon.getIconHeight();
    iconWidth =  unexpandedIcon.getIconWidth();
  }

  public TreeIconExample()  {  }

  public static void main(String ... arguments)
  {
    JFrame frame = new JFrame("icon test");
    frame.setBackground(Color.blue);
    JLabel label = new JLabel("background test");
    label.setBackground(Color.magenta);
    TreeIconExample treeIcon = new TreeIconExample();
    ImageIcon icon = treeIcon.getIcon(2, false);
    label.setIcon(icon);
    frame.add(label);
    frame.pack();
    frame.setVisible(true);
  }

  /**
   * return the icon for an expanded or unexpanded level
   * @param int level of folder relative to other levels displayed;
   * starts at 0 and increases with depth
   * @param boolean indicates whether this level is expanded or not.
   * @return ImageIcon appropriate for expansion flag and level.
   */
  public ImageIcon getIcon(int level, boolean expanded)
  {
    ImageIcon result = null;

    // generate this icon and store it in the cache before returning it.
    ImageIcon baseIcon = unexpandedIcon;
    if (expanded) { baseIcon = expandedIcon; }
    int iconH = iconHeight;
    int iconW = iconWidth*(level+1);

    BufferedImage bufferedImage = new BufferedImage(iconW,iconH,BufferedImage.TYPE_INT_ARGB);
    Graphics g = bufferedImage.getGraphics();

    g.fillRect(0, 0, iconW, iconH);
    g.drawImage(baseIcon.getImage(), iconWidth*level, 0, null);
    result = new ImageIcon(bufferedImage);

    return result;
  }
}

这是我的结果:

我想做的是去掉图标的白色部分；我希望它是透明的，这样 JLabel 的背景就会显示出来。我不知道为什么这个程序中既没有出现洋红色也没有出现蓝色；如果有人愿意告诉我这一点，我将不胜感激。但图像上的透明背景是我想弄清楚的主要问题。

Answer 1

the transparent background on the image is the main thing

它不透明的原因是你明确地用不透明的默认颜色填充它:-)

Graphics g = bufferedImage.getGraphics();
say("" + g.getColor());
g.fillRect(0, 0, iconW, iconH);

输出:

java.awt.Color[r=255,g=255,b=255]

所以要么不填充，要么使用完全/部分透明的颜色。

I don't know why neither magenta nor blue show up in this program; if someone cares to tell me that, I'd appreciate it

• (已在较早的帖子中回答)洋红色未显示，因为标签默认为 !opaque:这意味着其背景未填充其背景色
• 蓝色没有显示，因为您将它设置为被其 contentPane 覆盖的框架:默认情况下，后者是一个普通的 JPanel，不透明度默认为 true，即它用背景填充其区域

要看到蓝色，请将其设置为 contentPane 的背景色或更改其不透明度:

frame.getContentPane().setBackground(Color.blue);
// or
frame.setBackground(Color.YELLOW);
((JComponent) frame.getContentPane()).setOpaque(false);