Wt Riker Wt Riker - 29 days ago 20
Java Question

Centering Spanned Columns with GridBagLayout

I have a JDialog in which I have a series of columns over which I want to center a JLabel. I cannot seem to find anything on how to do that. I can center it within a cell but not within a spanned set of columns. The labels in this image "Target" and "Change" need to be centered.
Time Line Settings

Here is the SSCCE that produces this JDialog.

package stokerMonitor;

import java.awt.Dimension;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.Dialog.ModalityType;

import javax.swing.JDialog;
import javax.swing.JLabel;
import javax.swing.JSeparator;
import javax.swing.SwingConstants;


public class test {

static JDialog timeLineDialog;
static int row=0;

public static void main(String[] args) {
timeLineDialog = new JDialog();
timeLineDialog.setLayout(new GridBagLayout());
timeLineDialog.setModalityType(ModalityType.MODELESS);
timeLineDialog.setTitle("Time Line Settings");
timeLineDialog.setDefaultCloseOperation(JDialog.DO_NOTHING_ON_CLOSE);
JLabel timeLabel = new JLabel("Time");
JLabel actionLabel = new JLabel("Action");
JLabel probeTempLabel=null;
JLabel pitTempLabel=null;
JLabel targetHeader=new JLabel("Target");
Font boldFont=targetHeader.getFont().deriveFont(Font.BOLD, (float) 14);
targetHeader.setFont(boldFont);
JLabel changeHeader=new JLabel("Change");
changeHeader.setFont(boldFont);
if (Configuration.getInstance().celsius) {
probeTempLabel = new JLabel("Temp (\u00B0 C)");
pitTempLabel = new JLabel("Temp (\u00B0 C)");
}
else {
probeTempLabel = new JLabel("Temp (\u00B0 F)");
pitTempLabel = new JLabel("Temp (\u00B0 F)");
}
JLabel meatLabel=new JLabel("Meat");
JLabel cookTimeLabel=new JLabel("Est. Time");
JLabel weightLabel=new JLabel("Weight");
JLabel probeLabel=new JLabel("Probe");
JLabel pitLabel=new JLabel("Pit");
setNewSeparator(1,row);
GridBagConstraints gbc=makeGbc(2, row);
gbc.gridwidth=7;
gbc.fill=GridBagConstraints.HORIZONTAL;
gbc.anchor=GridBagConstraints.CENTER;
timeLineDialog.add(targetHeader,gbc);
setNewSeparator(9,row);
timeLineDialog.add(changeHeader,makeGbc(10, row));
setNewSeparator(12,row++);
setNewSeparator(1,row);
timeLineDialog.add(timeLabel, makeGbc(2, row));
timeLineDialog.add(probeTempLabel,makeGbc(3, row));
timeLineDialog.add(meatLabel,makeGbc(4, row));
timeLineDialog.add(weightLabel,makeGbc(5, row));
timeLineDialog.add(cookTimeLabel,makeGbc(6, row));
timeLineDialog.add(probeLabel,makeGbc(7, row));
timeLineDialog.add(actionLabel, makeGbc(8, row));
setNewSeparator(9,row);
timeLineDialog.add(pitLabel,makeGbc(10, row));
timeLineDialog.add(pitTempLabel, makeGbc(11, row++));
setNewSeparator(12,row);
timeLineDialog.pack();
timeLineDialog.setLocationRelativeTo(GUI.getInstance().getFrame());
timeLineDialog.setVisible(true);
}

static void setNewSeparator(int column_,int row_) {
JSeparator sep=new JSeparator(SwingConstants.VERTICAL);
sep.setPreferredSize(new Dimension(1,1));
GridBagConstraints gbc=makeGbc(column_, row_);
gbc.fill=GridBagConstraints.VERTICAL;
gbc.weighty=1.;
timeLineDialog.add(sep,gbc);
}

static GridBagConstraints makeGbc(int x, int y) {
GridBagConstraints gbc = new GridBagConstraints();
Insets WEST_INSETS=new Insets(5,0,5,5);
Insets EAST_INSETS=new Insets(5,5,5,0);
gbc.gridx = x;
gbc.gridy = y;
gbc.gridwidth = 1;
gbc.gridheight = 1;

gbc.anchor = (x == 0) ? GridBagConstraints.WEST : GridBagConstraints.EAST;
gbc.fill = (x == 0) ? GridBagConstraints.BOTH
: GridBagConstraints.HORIZONTAL;

gbc.insets = (x == 0) ? WEST_INSETS : EAST_INSETS;
gbc.weightx = (x == 0) ? 0.1 : 1.0;
gbc.weighty = 1.0;
return gbc;
}
}


Can someone explain what I need to do to center those headers? TIA.

dsh dsh
Answer

Tip: when debugging layouts, I find it useful to set each component to have a different background color. Then I can see the area assigned to / filled by that particular component. Most components default to a transparent background, which means their bounds is not visible. (eg targetHeader.setOpaque(true); targetHeader.setBackground(Color.RED);)

The situation you have with your layout is that the JLabel fills the 7 columns you specified. However, the label itself draws the text it contains in the leftmost part of the space that it fills.

There are two alternative solutions:

  1. Tell the label that you want it to center the text within the label: targetHeader.setHorizontalAlignment(JLabel.CENTER);

  2. Alternatively, you can tell the layout to not fill the space. gbc.fill=GridBagConstraints.NONE;