I am trying to change the dropdown arrow for a JComboBox with a custom image, but the code doesn't seem to work. I followed instructions from here. I tried with both Java 1.8.131 and AdoptOpenJDK 11.0.5, but the result is the same for both of them. Below you can find the full code that I am using:
Main.java
public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
JFrame f = new JFrame("Window");
JPanel panel = new JPanel();
panel.setBounds(0, 0, 400, 400);
panel.setBackground(Color.gray);
JComboBox<String> box = new JComboBox<>();//simple JComboBox with custom UI
box.setPreferredSize(new Dimension(150, 30));
box.setUI(MyBasicComboboxUI.createUI(box));
box.addItem("BasicComboBoxUI1");
box.addItem("BasicComboBoxUI2");
box.addItem("BasicComboBoxUI3");
panel.add(box);
JButton btn = new JButton("SimpleJButton");//simple JButton with an image on it (to prove that the image loads)
btn.setPreferredSize(new Dimension(120, 30));
MyImageProvider imageProvider = new MyImageProvider();
btn.setIcon(new ImageIcon(imageProvider.getImage()));
btn.setBorder(new EmptyBorder(0, 0, 0, 0));
panel.add(btn);
f.add(panel);
f.setSize(400, 400);
f.setLayout(null);
f.setVisible(true);
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
}
MyBasicComboboxUI.java:
public class MyBasicComboboxUI extends BasicComboBoxUI {
public static ComboBoxUI createUI(JComponent c) {
return new MyBasicComboboxUI();
}
@Override
protected JButton createArrowButton() {
JButton arrowButton = super.createArrowButton();
MyImageProvider imgProvider = new MyImageProvider();
arrowButton.setSize(new Dimension(40, 40));
arrowButton.setToolTipText("My tooltip");
arrowButton.setIcon(new ImageIcon(imgProvider.getImage()));//set the same icon here
arrowButton.setBorder(new EmptyBorder(0, 0, 0, 0));
return arrowButton;
}
}
MyImageProvider.java
public class MyImageProvider {
public Image getImage() {
try {
Image img = ImageIO.read(getClass().getResource("/icons/arrow.gif"));
return img;
} catch (IOException e) {
System.out.println("The image was not loaded.");
}
return null;
}
}
Image used 12px x 12px:
Image at 24px x 24px:
Output when running the program:
The tooltip set on the arrow is working. The same if I use a custom background color. But not if I set an image. I tried with: *.jpg, *.gif, *.png and different resolutions: 16x16, 14x14, 12x12, 8x8 etc. but with no success. In all cases the image loaded only on the SimpleJButton, but not on the drop down arrow button of the combobox.
Eclipse structure:
Your problem is the line
JButton arrowButton = super.createArrowButton();
you should change it to
JButton arrowButton = new JButton();
Background: super.createArrowButton() return an instance of the ArrowButton class, that provides custom arrow painting and does not support setIcon method.