在java中，如何将JPanel添加到另一个JPanel

Question

I wish to add 3 JPanels, all spaced different distances apart, that fill the Content Pane/JFrame. Currently, add(new JPanel()) will overrite the current content pane or not show up at all.

Ideally I want the code to resemble (for example's sake):

JPanel panel1 = new JPanel();
panel1.add(new jbutton())
panel1.setBounds(0,0,100,100);

JPanel panel2 = new JPanel();
panel2.add(new jbutton());
panel2.setBounds(100,0,100,100);

getContentPane().add(panel1);
getContentPane().add(panel2);

Etc...

I know a panel can be added to a panel because I've done it with borderlayout. Please don't tell me to use a layout manager, I've been using gridbag and it hasn't produced the results I want.

I would like full control over my objects' size and placement. Also, please don't tell me, "you're dumb; this is stupid; why would you ever want to do that?"

Only helpful responses please! I'm not a noob programmer, just a guy frustrated with GUIs, so feel free to go into as deep a depth as you'd like.

Answer 1

The content pane of a JFrame uses a BorderLayout by default, so each time you add a new panel to it, without specifying its location in the layout, it adds it to the center, and thus replaces the previous one.

Just set the content pane's layout to what you want. You may of course use the null layout (ie set the layout to null ), but you'll be bitten by this design mistake some time. Just because you've not been able to use layout managers doesn't mean that you shouldn't. Just keep learning. GridBagLayout is one of the most complex ones. You could use other ones first.

Answer 2

There's a good tutorial on Doing Without a Layout Manager that should help you. The most important recommendation it makes is to either use an IDE such as NetBeans , but it also covers doing things by hand.

Note that if you can't find a default LayoutManager that works for you, you can always write your own one - although in this case it sounds like JSplitPane is what you need - see How to Use Split Panes

Answer 3

I wish to add 3 JPanels, all spaced different distances apart, that fill the Content Pane/JFrame.

In you example the panels are not spaced different distances apart. The panels connect to one another. So all you need to do us use a panel with a FlowLayout that uses a horizontal gap of 0.

Your main code can be something like:

JPanel main = new JPanel( new FlowLayout(FlowLayout.CENTER, 0, 0) );

JPanel panel1 = new JPanel();
panel1.setPreferredSize( new Dimension(100, 100) );
panel1.add( new JButton() );
main.add( panel1 );

JPanel panel2 = new JPanel();
panel2.setPreferredSize( new Dimension(100, 100) );
panel2.add( new JButton() );
main.add( panel2 );

frame.add( main );

Given that you find layout code like this confusing, I would suggest you truly don't understand how to use layout managers. And like everybody else I suggest you take the time to understand how to use layout managers to your advantage.

By the way using a null layout does NOT make you life any easier. Sure you can place the components exactly where you want,but you do you satisfy your requirement that the panels take up the full space of the content pane? You won't be able to use the pack() method of the frame because when you use a null layout, your "main" panel won't have a preferred size so when you make the frame visible all you will see is the title bar and borders. If you manually try to set the size of the frame then yes you know the size of the 3 panels (300, x 100) but you don't know the size of the title bar and borders. So you won't be able to calculate the size properly.

It may take a few more minutes to understand layout managers but it is well worth it.

Answer 4

Layout managers will allow you to fully control your component placement and size, you just need to find the one that is simple enough for your application while giving you the amount of control you need. Doing without a layout manager is possible, but I would never suggest such a way of writing GUI code, you will end up managing way too many GUI stuff which are usually correctly managed by a LayoutManager (such as free space management, parent window resize..).

Most of the LayoutManager classes work in the same way; when you add a component to a Container , you also specify a constraint, which will tell the LayoutManager where to place the component, and how to handle all type of events that has an influence on the component placement (such as resizing the container). Some layout managers have very simple constraints ( BorderLayout only asks for the component location), whereas others have a very complet set of constraints ( GridBagLayout , via the GridBagConstraints class)

The LayoutManager I prefer is the GridBagLayout ( JavaDoc ). When correctly using the GridBagContraints class, you can specify where your widgets are displayed, what spacing there is to be between each component, how free space is distributed, etc.. This tutorial should help you getting started with this layout manager.

If this one does not suit your needs, or if you feel it is too complex, you should search the web for tutorials on other LayoutManager .