How to right-justify icon in a JLabel?

问题

For a JLabel with icon, if you setHorizontalTextPosition(SwingConstants.LEADING), the icon is painted right after text, no matter how wide the label is.

This is particularly bad for a list, as the icons would be all over the place depending on how long the text is for each item.

I traced the code and it seems to be that in SwingUtilities#layoutCompoundLabelImpl, text width is simply set to SwingUtilities2.stringWidth(c, fm, text), and icon x is set to follow text without considering label width.

Here is the simplest case:

import java.awt.*;
import javax.swing.*;

public class TestJLabelIcon
{
    public static void main(String args[])
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                JLabel c = new JLabel("abc");
                c.setHorizontalTextPosition(SwingConstants.LEADING);
                c.setHorizontalAlignment(SwingConstants.LEADING);
                c.setIcon(UIManager.getIcon("FileChooser.detailsViewIcon"));
                c.setBorder(BorderFactory.createLineBorder(Color.RED));

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
                frame.getContentPane().add(c);    
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

You can see that label always fills the frame but icon stays put. You'll get the mirror problem if you set both arguments to TRAILING.

I know I can override the UI, or use a JPanel, etc. I just wonder if I'm missing something simple in JLabel. If not, it seems like a Java bug.

FYI this is jdk1.6.0_06 on Windows XP.

回答1:

Is this the desired effect?

Addendum: I think a panel is the way to go.

import java.awt.*;
import javax.swing.*;

public class TestJLabelIcon {

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.setLayout(new GridLayout(0, 1));
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(createPanel("abc"));
                frame.add(createPanel("defghij"));
                frame.add(createPanel("klmn"));
                frame.add(createPanel("opq"));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

            private JPanel createPanel(String s) {
                JPanel p = new JPanel(new BorderLayout());
                p.add(new JLabel(s, JLabel.LEFT), BorderLayout.WEST);
                Icon icon = UIManager.getIcon("FileChooser.detailsViewIcon");
                p.add(new JLabel(icon, JLabel.RIGHT), BorderLayout.EAST);
                p.setBorder(BorderFactory.createLineBorder(Color.blue));
                return p;
            }
        });
    }
}

回答2:

You should use:

label1.setHorizontalTextPosition(SwingConstants.LEFT);

(Set the position of the text, relative to the icon)

回答3:

I found a much easier way to do this. I needed to have this kind of layout in a JTable, and did the right justification by getting the text width and then manually setting the width between the text and the icon. I subclassed a DefaultTableCellRenderer for my JTable

public class FixedWidthRenderer extends DefaultTableCellRenderer 
{
    ...
    @Override
    public Component getTableCellRendererComponent(JTable table, Object value, 
        boolean isSelected, boolean hasFocus, int row, int column)
    {
        ...
        FontMetrics met = super.getFontMetrics(super.getFont());
        int width = met.stringWidth(super.getText());                
        super.setIconTextGap(DESIREDWIDTH - width); 
        ...
    }
}

Works great!
And yes, for real code one should check that the text width is not bigger than the DESIREDWIDTH.

---

For automatic right-alignment without a fixed width that works with columns of variable width:

    @Override
    public void setBounds(int x, int y, int width, int height) {
        super.setBounds(x, y, width, height);
        if (getIcon() != null) {
            int textWidth = getFontMetrics(getFont()).stringWidth(getText());
            Insets insets = getInsets();
            int iconTextGap = width - textWidth - getIcon().getIconWidth() - insets.left - insets.right - PADDING;
            setIconTextGap(iconTextGap);
        } else {
            setIconTextGap(0);
        }
    }

来源：https://stackoverflow.com/questions/2932389/how-to-right-justify-icon-in-a-jlabel