GridBagLayout : Java Glossary

Typical Use

GridBagConstraints Fields

If your GridBagLayout does not work, here are some things to check:

• Did you remember your setLayout? If you did not, you are using the default FlowLayout.
• Do you have two Components in the same grid square?
• Did you have any setBounds or setLocation calls on the Components? These are not needed, and will sometimes interfere.
• Did you remember to setConstraints or add ( Component, Constraints) for every Component?
• Did you add Component to a unrelated JPanel. This often happens when you cut and paste code.
• Did you use the GridBagConstraints object you intended for each Component? You may be juggling several of them at once.
• Did you remember to add the Component to the Container?
• It is ok to use the same GridBagConstraints model object for two different squares and modify the fields for the second Component. Those changes won’t affect the first Components so long as you did a setConstraints (which snapshots/clones/copies the Constraints before you made the changes.
• Did you remember to set gridwidth and gridwidth to a non-zero value? fill = GridBagConstraints.BOTH; is not sufficient no make Components grow to fill the space.
• I’d call this a bug, but I find layouts like to have at least one component in each column that does not slop into any other columns, and one component in each row that does not slop over into other rows. In other words each row needs an element with height=1 and each column needs a element with width=1. This is not a hard and fast rule, but if you find your layouts acting strangely, you can try the trick of adding dummy elements e.g. a blank label to satisfy this condition.

1. Draw a crude overall diagram, such as this one from my Quoter Amanuensis:

   // Applet Gridbag:
   //     0       1        2
   // --------title---  about  0
   // --------raw----------    1
   // -------cooked--------    2
   //  Charset  Clear  Convert 3
   //  target                  4
   //  trim                    5
   // -----instructions-----   6

2. Label it with GridBagLayout co-ordinates.
3. Get the gridx, gridy, gridheight and gridwidth parms right.
4. Set your various alignment parameters, both within the Components and within the GridBagLayout’s anchor.
5. If some Components are too small, stretch with fill.
6. Put some ipadx and ipady around buttons to plumpen them up. This does not request more white space the way the Insets do, this leaves some room for the component itself to grow in. You would typically use it for a JLabel to account for the fact later setTexts might need a larger label. You want to leave room so the whole layout does not adjust every time you setText to a longer value. ipadx is the padding added to either end measured in pixels. It works by setting the adding ipadx * 2 to the mimimum width.
7. Fine tune with insets to get the spacing right. Focus at first on getting the insets for the outer margins, then spacing between Components. In Swing, setting the outer margins is done much more easily using a border. It is very fiddly with insets. Also there’s an argument to use spacer components instead of insets. Insets get very fiddly, particularly when the Metal styleguide demands odd numbered spacings. Try it both ways and see which suits you better.
8. Fiddle with weightx and weighty so that your layout still looks good when you grow or shrink it.
9. Ask your artist lover to look at the design and tell you where it needs adjustment. Unfortunately mine left a decade ago, so my designs look quite wooden.

ContentPane

this.setLayout( gridBagLayout );
this.add( aButton, constraints );

Container contentPane = this.getContentPane();
contentPane.setLayout( gridBagLayout );
contentPane.add( aButton, constraints );

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