如何定位按钮？

Question

How do I position buttons exactly where I want them to be. I have a background image set to the main panel. then the 2 buttons are on top next to each other But I want them to be in the center . on top of each other like in a main menu.

I have tried all ways nothing works the closest I am getting is by using Box Layout. Here is the code and image of how it looks. but I need the buttons to be in center.

public Menu() {
    JFrame frame = new JFrame("Fruit Catcher");
    JPanel panel = new JPanel();

    frame.add(panel);


    ImageIcon junglebackground = new ImageIcon("junglebackground.jpg");
    JLabel backgroundimage = new JLabel(junglebackground);

    frame.add(backgroundimage);
    frame.setSize(700,470);
    frame.setResizable(false);
    frame.setVisible(true);


    JPanel buttonPanel = new JPanel();
    buttonPanel.setLayout(new BoxLayout(buttonPanel, BoxLayout.Y_AXIS));        

    JButton Play = new JButton("Play");
    JButton Scoreboard = new JButton("Scoreboard");
    Play.setAlignmentX(Component.CENTER_ALIGNMENT);
    JLabel gap = new JLabel("\n");
    Scoreboard.setAlignmentX(Component.CENTER_ALIGNMENT);


    buttonPanel.add(Play);
    buttonPanel.add(gap);
    buttonPanel.add(Scoreboard);



    frame.add(buttonPanel);


}

Answer 1

Nest JPanels

• Place the buttons in a JPanel that uses GridLayout(0, 1, 0, vertGap) which stands for a grid with a variable number of rows, 1 column, 0 horizontal gaps (since there is only one column) and vertGap vertical gap -- an int value that you must decide on.
• Then place this JPanel into your main JPanel.
• If you want it at the top and centered, you could have the main JPanel simply use its default FlowLayout.
• If you want the image to show through the GridLayout using JPanel, be sure to set it to non-opaque by calling, setOpaque(false) .
• Most importantly, read up on how to use layout managers in the Swing tutorials. You can find links to the Swing tutorials and to other Swing resources here: Swing Info .

Answer 2

You should further read whatever introduction to swing you had. Later on, they are bound to talk about Layouts , which are ways to define how buttons should be layed out in your window.

What you're describing sounds like you could solve it with some grid layout, but it's hard to guess what exactly you need, so it might be best if you find out yourself.

Answer 3

Since you know the background image is larger that the buttons you want to disply, you can use the JLabel as a Container for your buttons. The basic code would be:

JFrame frame = new JFrame("Fruit Catcher");

ImageIcon jungleBackground = new ImageIcon("junglebackground.jpg");
JLabel backgroundImage = new JLabel(junglebackground);
frame.add( backgroundImage)

Now you need to add the buttons to the label. Two options:

Use a BoxLayout on the label:

backgroundImage.setLayout(new BoxLayout(backgroundImage, BoxLayout.Y_AXIS));  
backgroundImage.add( Box.createVerticalGlue() );
backgroundImage.add( new JButton("Play") );
backgroundImage.add( Box.createVerticalStrut(20) );
backgroundImage.add( new JButton("Scoreboard") );
backgroundImage.add( Box.createVerticalGlue() );

Read the section from the Swing tutorial on How to Use Box Layout for more information and examples.

Another choice is to use a GridBagLayout on the label:

backgroundImage.setLayout( new GridBagLayout() );
GridBagConstraints gbc = new GridBagConstraints();

backgroundImage.add(new JButton("Play"), gbc);
gbc.gridy = 1;
gbc.insets = new Insets(10, 0, 0, 0);
backgroundImage.add(new JButton("Scoreboard"), gbc);

Don't forget to read the tutorial for more information about the GridBagConstraints .

Finally, once all the components are added to the frame you would do:

frame.pack();
frame.setResizable(false);
frame.setVisible(true);