How do I get a JPanel with an empty JLabel to take up space in a GridBagLayout

Question

I am working on a GUI for a project at school. I am using a GridBagLayout in swing.

I want to have a label indicating the input(a type of file @ x = 0, y = 0), followed by another label(the actual file name once selected @ x = 1, y = 0), followed by a browse button for a file chooser( @ x = 2, y = 0). The label at (1,0) is initially blank, however I want the area that the text will occupy to take up some space when the label contains no text. I also want the space between the label at (0,0) and the button at (2,0) to remain constant.

To achieve this, I'm trying to put the label onto a panel and then play with the layouts. However I can't seam to achieve the desired results. Could anyone offer some suggestions? The next three rows of the GridBagLayout will be laid out exactly the same way.

Here is a link to a screen shot of the GUI.

    calibrationFileSelectionValueLabel = new JLabel("",Label.LEFT);
    calibrationFileSelectionValueLabel.setName("calibrationFileSelection");
    calibrationFileSelectionValueLabel.setMinimumSize(new Dimension(100,0));



    calibrationFileSelectionValuePanel = new JPanel();
    calibrationFileSelectionValuePanel.setBorder(BorderFactory.createEtchedBorder());
    calibrationFileSelectionValuePanel.add(calibrationFileSelectionValueLabel);

    c.gridx = 0;
    c.gridy = 0;
    c.fill = GridBagConstraints.NONE;

    filesPanel.add(calibrationFileLabel,c);

    c.gridy = 1;
    filesPanel.add(frequencyFileLabel,c);

    c.gridy = 2;
    filesPanel.add(sampleFileLabel,c);

    c.gridy = 3;
    filesPanel.add(outputFileLabel,c);

    c.gridx = 1;
    c.gridy = 0;
    c.fill = GridBagConstraints.BOTH;

   // filesPanel.add(calibrationFileSelection,c);
    filesPanel.add(calibrationFileSelectionValuePanel,c);

    c.gridy = 1;
   // filesPanel.add(frequencyFileSelection,c);
    filesPanel.add(frequencyFileSelectionValueLabel,c);

    c.gridy = 2;
   // filesPanel.add(sampleFileSelection,c);
    filesPanel.add(sampleFileSelectionValueLabel,c);

    c.gridy = 3;
   // filesPanel.add(outputFileSelection,c);
    filesPanel.add(outputFileSelectionValueLabel,c);

    c.gridx = 2;
    c.gridy = 0;
    c.fill = GridBagConstraints.NONE;
    filesPanel.add(calibrationFileSelectionButton,c);

    c.gridy = 1;
    filesPanel.add(frequencyFileSelectionButton,c);      

    c.gridy = 2;
    filesPanel.add(sampleFileSelectionButton,c);

    c.gridy = 3;
    filesPanel.add(createOutputFileButton,c);       

    panelForFilesPanelBorder = new JPanel();
    panelForFilesPanelBorder.setBorder(BorderFactory.createCompoundBorder(new EmptyBorder(5,10,5,10), BorderFactory.createEtchedBorder()));
    panelForFilesPanelBorder.add(filesPanel);

    buttonsPanel = new JPanel();
    buttonsPanel.setLayout(new FlowLayout(FlowLayout.CENTER));
    buttonsPanel.setBorder(BorderFactory.createCompoundBorder(new EmptyBorder(5,10,10,10), BorderFactory.createEtchedBorder()));
    buttonsPanel.add(startButton);
    buttonsPanel.add(stopButton);
    basePanel.add(panelForFilesPanelBorder);
    basePanel.add(numericInputPanel); 
    basePanel.add(buttonsPanel); 

Answer 1

Well, Essentially, GridBagLayout places components in rectangles (cells) in a grid, and then uses the components' preferred sizes to determine how big the cells should be. With this layout:

• if the container's size is smaller than the preferred size only then the minimum size gets used.
• With empty("") text A JLabel\JTextFeild\JButton's preferred size is around (2,2), if no preferred size hints is given to it explicitly using setPreferredSize(size) or overriding getPreferredSize(size).

At his point setting minimum size will not work, as the preferred size with empty text is around (2,2) and container's size is already larger than the preferred size. GridBagLayout uses the preferred size not worrying about the minimum size at all.

You actually need to set both preferred and minimum size with GridBagLayout because:

If you try setting only the preferred size, shrinking the size of the window would eventually cause the container panel's size to get shrink. The container's panel size will be smaller than the preferred size of the component and the JLabel\JTextFeild\JButton shrink to their minimum size. If you haven't given minimum size hints at this point, the default minimum size: likely to be around (2,2) gets used. You will understand better with given working example below.

Some other things to note:

   c.gridx = 1;
    c.gridy = 0;
    c.fill = GridBagConstraints.BOTH;

   // filesPanel.add(calibrationFileSelection,c);
    filesPanel.add(calibrationFileSelectionValuePanel,c);

you are adding the panel which contains your calibrationFileSelectionValueLabel. You don't need to use an extra panel, rather just add the calibrationFileSelectionValueLabel directly to the grid by setting( instead overriding getPreferedSize(Size) is preferable) preferredSize. However try setting inset to the GridBagConstraints to look your first panel a little more nicer:

   gridBagCnst.insets = new Insets(3, 3, 3, 3); 

A minimal working example for you:

In case you are not getting what we are saying, this example i have set only preferred size for resolving your problem. But as i haven't set minimum size, try resizing the window to match with above explanation.

Source code:

import java.awt.*;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.Insets;
import javax.swing.*;
import javax.swing.SwingUtilities;
import javax.swing.border.*;


/**
 *
 * @author Rashed
 */
 class GridBagLayoutDemo extends JFrame{


    public JLabel createLabel(String txt, int width, int height, Color color)
    {
        JLabel label = new JLabel(txt);
        label.setOpaque(true);
        label.setBackground(color);
        label.setPreferredSize(new Dimension(width, height));
        return label;
    }

    public GridBagLayoutDemo() throws HeadlessException {
      // setSize(400,400);
       setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

       JPanel panel = new JPanel(new java.awt.GridBagLayout());
       panel.setBorder(new EmptyBorder(10, 10, 10, 10));
       GridBagConstraints labCnst = new GridBagConstraints();

       Dimension preferredSize = new Dimension(140,20);

       labCnst.insets = new Insets(3, 3, 3, 3);

       JLabel title = new JLabel("My Title");
       JLabel title2 = new JLabel("My Title");
       JLabel title3 = new JLabel("My Title");

       JLabel selectionLabel1 = new JLabel("");
       selectionLabel1.setBorder(new LineBorder(Color.BLACK));
       JLabel selectionLabel2 = new JLabel("");
       selectionLabel2.setBorder(new LineBorder(Color.BLACK));
       JLabel selectionLabel3 = new JLabel("");
       selectionLabel3.setBorder(new LineBorder(Color.BLACK));

       selectionLabel1.setPreferredSize(preferredSize);
       selectionLabel2.setPreferredSize(preferredSize);
       selectionLabel3.setPreferredSize(preferredSize);

       JButton browse1 = new JButton("Browse");
       JButton browse2 = new JButton("Browse");
       JButton browse3 = new JButton("Browse");


        labCnst.gridx = 0;
        labCnst.gridy = 0;
        panel.add(title, labCnst);
        labCnst.gridy = 1;
        panel.add(title2, labCnst);
        labCnst.gridy = 2;
        panel.add(title3, labCnst);

        labCnst.gridx = 1;
        labCnst.gridy = 0;
        panel.add(selectionLabel1, labCnst);
        labCnst.gridy = 1;
        panel.add(selectionLabel2, labCnst);
        labCnst.gridy = 2;
        panel.add(selectionLabel3, labCnst);

        labCnst.gridx = 3;
        labCnst.gridy = 0;
        panel.add(browse1, labCnst);
        labCnst.gridy = 1;
        panel.add(browse2, labCnst);
        labCnst.gridy = 2;
        panel.add(browse3, labCnst);


       //labCnst.anchor = GridBagConstraints.LINE_END;


       add(panel);
       pack();

    }


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

            @Override
            public void run() {
                new GridBagLayoutDemo().setVisible(true);
            }
        });
    }
}