简单的GUI Java布局问题

Question

I'm trying to do the following and I'm not sure what type of Java layout to use.

I want a JFrame with a single panel totalPanel . totalPanel should contain two panels which are custom classes I write, PanelA and PanelB. PanelA starts out with height 200 and PanelB starts out with height 400. When the user expands the window or resizes the window, only PanelB should increase in height, but both panels can increase in width.

How can I set this up? I've tried to use BorderLayout but then "North" is always too small in height. I've tried to use BoxLayout but then both PanelA and PanelB are always the same height.

Answer 1

Consider having totalPanel use a BorderLayout. Add the PanelA to the BorderLayout.PAGE_START position and the PanelB to the BorderLayout.CENTER position.

For more on the layout managers, please review the tutorial: Lesson: Laying Out Components Within a Container

Edit: I see that you've used BorderLayout, that it "doesn't work" but you don't show code. For more fine tuning on why it doesn't work, consider showing us code.

To get it to work consider giving your PanelX classes getPreferredSize() overrides that would help set the initial sizes of the JPanels.

For example:

import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.*;

public class SimpleGuiLayout {

   private static void createAndShowGui() {
      JPanel totalPanel = new JPanel(new BorderLayout());

      totalPanel.add(new PanelX(800, 200, "Panel A"), BorderLayout.PAGE_START);
      totalPanel.add(new PanelX(800, 400, "Panel B"), BorderLayout.CENTER);
      JFrame frame = new JFrame("Simple Gui Layout");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(totalPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

class PanelX extends JPanel {
   private int prefW;
   private int prefH;

   public PanelX(int prefW, int prefH, String title) {
      this.prefW = prefW;
      this.prefH = prefH;
      setBorder(BorderFactory.createTitledBorder(title));
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(prefW, prefH);
   }
}

If run, it would look like so:

And would resize appropriately.

Answer 2

One approach (probably not the simplest) would be a GridBagLayout.

Use the weightx and weighty constraints to control which members can resize.

Answer 3

I recommend a GridBagLayout. It is complex to use, but it can solve your problem. Assuming panelA is on top of panelB, you would have the following constraints:

• panelA and panelB's gridx would be 0
• panelA would be ad gridy 0, and panelB at gridy 1
• for both, you would set fill = BOTH
• but to have only panelB increase in height, you would set panelB's weighty to 1.0, and panelA's to 0

Answer 4

You originally solution using BorderLayout will work already, you just need to set preferred height of panelA:

    panelA.setPreferredSize(new Dimension(0, 200));

The width doesn't matter because BorderLayout will ignore preferred width of component added to NORTH or SOUTH.