How to use GridBagConstraints to create the layout?

Question

I want to layout my JPane like so:

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|     |
|     |
|     |
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|     |
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This way, the top section is bigger/taller than

Answer 1

In general, for gridbag layout

• if you want a component scale, you must give its scale direction a weight, and any sizes (width/height) you set for that direction will be ignored by the layout manager.

• If you don't want a component scale, the component must have its size defined (if you want, you can dig into this topic in documents of java). In your case of the bottom panel, you need to give its, at least, a preferred height.

This can work as your expectation

pnlTop.setBackground(Color.WHITE);
pnlBottom.setBackground(Color.BLUE);

// Because you don't want the bottom panel scale, you need to give it a height.
// Because you want the bottom panel scale x, you can give it any width as the
// layout manager will ignore it.
pnlBottom.setPreferredSize(new Dimension(1, 20));


getContentPane().setLayout(new GridBagLayout());
GridBagConstraints cst = new GridBagConstraints();
cst.fill = GridBagConstraints.BOTH;
cst.gridx = 0;
cst.gridy = 0;
cst.weightx = 1.0; // --> You miss this for the top panel
cst.weighty = 1.0;
getContentPane().add(pnlTop, cst);

cst = new GridBagConstraints();
cst.fill = GridBagConstraints.HORIZONTAL;
cst.gridx = 0;
cst.gridy = 1;
cst.weightx = 1.0; // You miss this for the bottom panel
cst.weighty = 0.0;
getContentPane().add(pnlBottom, cst);

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Further more, if you want to use gridbag layout, I recommend you to try the painless-gridbag library http://code.google.com/p/painless-gridbag/ (I'm the author of that library). It doesn't solve this problem for you (as your problem concerns managing component's size in gridbag layout) but it will save you a lot of typing and make your code easier to maintain

pnlBottom.setPreferredSize(new Dimension(1, 20));

PainlessGridBag gbl = new PainlessGridBag(getContentPane(), false);
gbl.row().cell(pnlTop).fillXY();
gbl.row().cell(pnlBottom).fillX();
gbl.done();