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javaswinggridbaglayout

GridBag not displaying all components in row

I've implemented a JPanel using a GridBagLayout as follows:

fileSelectionDetails = new JPanel();
fileSelectionGridBagLayout = new GridBagLayout();
fileSelectionDetails.setLayout(fileSelectionGridBagLayout);


JLabel lblFile1 = new JLabel("File 1:");
JTextField txtFile1Path = new JTextField();    
JButton btnBrowseFile1 = new JButton("Browse...");

addComponentToFileSelectionGrid(lblFile1, 0, 0, 1, 1, 20, 100, GridBagConstraints.NONE, GridBagConstraints.WEST);
addComponentToFileSelectionGrid(txtFile1Path, 1, 0, 3, 1, 60, 100, GridBagConstraints.HORIZONTAL, GridBagConstraints.WEST);
addComponentToFileSelectionGrid(btnBrowseFile1, 2, 0, 1, 1, 20, 100, GridBagConstraints.HORIZONTAL, GridBagConstraints.WEST);

private void addComponentToFileSelectionGrid(Component component, int gridX, int gridY,
                            int gridWidth, int gridHeight, int weightX, 
                            int weightY, int fill, int anchor) {

    GridBagConstraints constraint = new GridBagConstraints();
    constraint.gridx = gridX;
    constraint.gridy = gridY;
    constraint.gridwidth = gridWidth;
    constraint.gridheight = gridHeight;
    constraint.weightx = weightX;
    constraint.weighty = weightY;       
    constraint.fill = fill;
    constraint.anchor = anchor;
    fileSelectionGridBagLayout.setConstraints(component, constraint);
    fileSelectionDetails.add(component);
}

I want to see my components laid out as follows:

enter image description here

However, what I'm actually seeing is:

enter image description here

i.e. the 'Browse...' button is missing! Why is this?

Solution

  • From your drawing, I’m guessing you don’t want relative widths at all. It appears you want the label and button to be their preferred sizes, and the JTextField to stretch to take up all of the width not used by the label and button.

    As camickr suggested, you should give the JTextField a meaningful preferred size by initializing it with a column count, like new JTextField(20).

    You can then take advantage of some useful aspects of GridBagLayout and GridBagConstraints:

    • The default value of gridx and gridy is RELATIVE, which means each component you add is placed to the right of the last one added. Which just happens to be exactly what you want. Therefore, you should not set gridx or gridy at all.
    • The default value of gridwidth and gridheight is 1. This is what you want. GridBagLayout cells are flexible, so setting one component’s gridwidth to 3 does not make it three times wider than a component whose gridwidth is 1. The width of a cell, or span of cells, depends entirely on what it contains.
    • When you add a component to a GridBagLayout, the GridBagConstraints object is cloned inside the GridBagLayout. This means you can safely reuse the same GridBagConstraints object over and over, changing just the fields that need to change.

    With this knowledge, your code can be simplified to:

    fileSelectionDetails = new JPanel(new GridBagLayout());

JLabel lblFile1 = new JLabel("File 1:");
JTextField txtFile1Path = new JTextField(20);
JButton btnBrowseFile1 = new JButton("Browse\u2026");

txtFile1Path.setMinimumSize(txtFile1Path.getPreferredSize());

GridBagConstraints constraints = new GridBagConstraints();
constraints.fill = GridBagConstraints.HORIZONTAL;

constraints.weight = 0;
fileSelectionDetails.add(lblFile1, constraints);
constraints.weight = 1;
fileSelectionDetails.add(txtFile1Path, constraints);
constraints.weight = 0;
fileSelectionDetails.add(btnBrowseFile1, constraints);