Is there anyway to "pack" a JPanel?

Question

Is there any thing I can do to make my JPanel pack like a JFrame, or do something like that. I want to do this instead of giving it dimensions. Please comment if any addition info is needed. Thanks.

Ashburn

pack uses the preferred size of the frames content to determine the best size for the frame...so, you need to have the size of the components in order to make it work. The best choice is to use appropriate layout managers...see Laying Out Components Within a Container – Calicut

@Calicut this is only one JPanel so I don't want to use a layout manager. – Ashburn

That's probably the worst single statement I've heard for some time, sorry. Then the answer to your question is no, there is no other way to do this, the API was designed from the start to make use of the layout managers. – Calicut

Avoid using null layouts, pixel perfect layouts are an illusion within modern ui design. There are too many factors which affect the individual size of components, none of which you can control. Swing was designed to work with layout managers at the core, discarding these will lead to no end of issues and problems that you will spend more and more time trying to rectify. Why is it frowned upon to use a null layout in SWING? – Calicut

@Calicut so what do you suggest I use instead of Swing for a null layout? – Ashburn

A layout manager. You've provided no context to the problem you are trying to solve so it's impossible to provide you with solution or suggest that might be of more use – Calicut

@Calicut What about a GroupLayout – Ashburn

Not my preferred layout manager, as it's not really designed for coders, but for UI editors, depending on the circumstances, I might consider GridBagLayout or maybe even MigLayout – Calicut

What about a GroupLayout - We have no idea what you requirement is so how do you expect us to answer that? The GroupLayout may be the most complicated to learn. Also, there is no reason to use a single layout manager since you can nest panels with different layout. – Blancablanch

@Blancablanch yeah you're right. – Ashburn

Answer 1

Please try JPanel.updateUI and let me know if that helps.

You should make GUI calls in the Event Dispatcher Thread:

EventQueue.invokeLater(() -> {
    someJPanel.updateUI();
});

Deuterium

For me the method updateUI has no effect on resizing a JPanel. – Kibe

Answer 2

If I understand you correctly, your JPanel is not being automatically (re)sized, correct? In that case, you can use Component.validate (or JComponent.revalidate())

Moralez

My real problem is that the JPanel is not fitting all the components I put in it, so you're right. My JPanel does originally fit its components so when it doesn't I tell my program to pack it, and then I no longer have to worry about it, instead of constantly adjusting it by hand as I add more components. I don't fully understand how to use the code you just gave me though. – Ashburn

@MattS, My JPanel does originally fit its components - which is why you should be using a layout manager. If you add components to a visible GUI then you simple revalidate() the panel. Post your SSCCE that demonstrates your problem. You were asked to do this as well in your last question. – Blancablanch

Answer 3

Let me explain my use case, so that my answer will make sense.

I have a game board G on which I am absolutely positioning tiles Ts and some other property panels say P, Q and R.

Only the Game board G doesn't use a layout. However, for all the tiles and other panels, I do want to use layout management. For the tiles, I want to calculate and set both position and size based on how many tiles are there. So, the setBounds method works great.

The problem is with the other panels like P where I know the x and y where I want to place them, however, I would like it if they figured out their own preferred sizes. This becomes a problem because setBounds insists on setting both position and size, and setLocation doesn't seem to work.

The solution which worked for me is putting a slightly oversized panel Outer-P and setting opaque to false and then placing P inside it. Note that Outer-P has a layout manager which allows P to be its preferred size. Personally, I used new MigLayout("insets 0","[]","[]") which lets the child take its preferred width and height.

As far as the user is concerned, P is in the top left, and looks packed. The wrapper panel is invisible.

Northeaster