Please help me understanding BoxLayout alignment issues

Question

I'm trying to create a very simple window using Java Layouts. I have got three elements to arrange: a button, a progress bar and a label. The button has to be vertically centered, the progress bar has to take full width, and the label has to be left aligned.

Here's some code (just assume pane is the content pane of a JFrame, and button, progressBar and label have been created before):

BoxLayout layout = new BoxLayout(pane, BoxLayout.Y_AXIS);
pane.setLayout(layout);
button.setAlignmentX(Component.CENTER_ALIGNMENT);
pane.add(button);
progressBar.setAlignmentX(Component.CENTER_ALIGNMENT);
pane.add(progressBar);
label.setAlignmentX(Component.LEFT_ALIGNMENT);
pane.add(label);

When I test the application I see everything misaligned and screwed up: the button and the label are randomly indented, and if I resize the window the indentation amount changes in a strange way. The progress bar looks good (full width).

I just don't understand what's happening. Can you give me a clue?

Croton

Personally, I never trust setAlignmentX or setAlignmentY and try to avoid them as plague, I also avoid layout managers that exclusively depend on them. – Dentoid

I now understand why you do so... What alternatives would you suggest? – Croton

Well, if you have to stick to pure JDK, then I'd probably use GridBagLayout in your case; that would work well because your layout is simple (GBL starts to be complex when your layout has more components). Otherwise, I would use DesignGridLayout. – Dentoid

Answer 1

Sometimes you need to get a little creative and use nested panels. But I like this approach better then trying to learn and memorize all the constraints required when using other layout managers (GridBagLayout, GroupLayout) there where designed to be used by IDE's that generate code for you.

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

public class BoxLayoutVertical extends JFrame
{
    public BoxLayoutVertical()
    {
        Box box = Box.createVerticalBox();

        JButton button = new JButton("A button");
        button.setAlignmentX(Component.CENTER_ALIGNMENT);
        box.add(button);

        JProgressBar progressBar = new JProgressBar(0, 100);
        progressBar.setAlignmentX(Component.CENTER_ALIGNMENT);
        box.add(progressBar);

        JPanel panel = new JPanel( new BorderLayout() );
        JLabel label = new JLabel("A label");
        label.setAlignmentX(Component.LEFT_ALIGNMENT);
        panel.add(label);
        box.add(panel);

        add(box, BorderLayout.NORTH);
    }

    public static void main(String[] args)
    {
        BoxLayoutVertical frame = new BoxLayoutVertical();
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.setSize(300, 200);
        frame.setLocationRelativeTo( null );
        frame.setVisible(true);
    }
}

Crucifer

Best solution ever, because involves no additional libraries, no additional classes, and it's tailored to the very issue I'm facing. However, I'll follow other users' solutions to learn more about layouts, but in this case I was looking for a simple hack. – Croton

Answer 2

BoxLayout cannot handle different alignments: see http://download.oracle.com/javase/tutorial/uiswing/layout/box.html

quoting from that article: "In general, all the components controlled by a top-to-bottom BoxLayout object should have the same X alignment. Similarly, all the components controlled by a left-to-right Boxlayout should generally have the same Y alignment."

Soll

Thanks, therefore BoxLayout is crap for me. I'll follow all of your hints. – Croton

Are you sure it cannot handle different alignments? docs.oracle.com/javase/tutorial/uiswing/layout/box.html – Nick

@AndrewS: Which part of the tutorial are you referring to, when you suggest that Box can handle different alignments? Does the solution involves using Box.createHorizontalGlue(), or is this possible otherwise? – Fetter

@Mins, look at sections by the image example entitled BoxLayoutDemo2. You will see that the components are aligned relative to one another using Component.LEFT_ALIGNMENT, Component.CENTER_ALIGNMENT and Component.RIGHT_ALIGNMENT. – Nick

@AndrewS: This doesn't work for me, I've posted the code in this question. What's wrong? – Fetter

@Fetter look up the section in the same document that demonstrates glue. Then experiment by putting glue in front of or behind the desired components. You could also try nesting your layouts too. – Nick

Answer 3

To complement my comment to the original question, here is a snippet that uses DesignGridLayout:

JButton button = new JButton("Button");
JProgressBar progressBar = new JProgressBar();
JLabel label = new JLabel("Label");

// The interesting stuff is in the next 4 lines
DesignGridLayout layout = new DesignGridLayout(getContentPane());
layout.row().center().add(button).withOwnRowWidth();
layout.row().center().fill().add(progressBar);
layout.row().left().add(label);

pack();

It does exactly what wou describe in your question and doesn't require any specific call of any of the components.

Dentoid

Answer 4

Maybe your code is just a snippet, but I'm missing a call to pack().

Coding swing layout by hand can be very frustrating with the standard Layout managers. I use MiG Layout for that purpose. It is straight forward and you have a nice layout with just a few lines of code. If you're not forced to use BoxLayout I would suggest you give it a try.

Dowland

I like this MiG layout, but I really don't want to link other JARs and push things to a more "complicated" level for a very, very simple application like this. – Croton

@Giacomo: Fair enough ;) The "missing" pack() wasn't the issue then? – Dowland

Answer 5

Don't use BoxLayout. It works only for very simple cases.

For your case, I would recommend either GridBagLayout or (my favorite) GroupLayout.

---

For GroupLayout, I created a subclass (LayoutHelper) with some utility methods and useful constructors, which makes writing the Layout much easier.

Of course, usually I align all components in a group the same way, so it is not as short in your case as it would be in the simple case.

    LayoutHelper h = new LayoutHelper(pane);

    h.setVerticalGroup
        ( h.sequential( button, progressBar, label));

    h.setHorizontalGroup
        ( ((ParallelGroup)h.parallel())
          .addComponent(button, Alignment.CENTER)
          .addComponent(progressBar)
          .addComponent(label, Alignment.TRAILING));

Here is a screenshot:

For a simple "everything aligned the same way", the horizontal group would look like this:

    h.setHorizontalGroup
        ( h.parallel (button, progressBar, label));

(optionally with a first argument indicating the alignment).

Melisandra

@Paulo you hand-code GroupLayout? Then you seem to have too much spare-time :-) – Soll

@kleopatra: I have a wrapper-class which facilates it a bit. (I'll add how it would look with this). A bare bones GroupLayout is not nice, but not much better than GridBagLayout. – Stour

@Giacomo: I don't know for what a BoxLayout is good, honestly. I also had only problems using it, especially the alignment orthogonal to its layout direction. – Stour