MigLayout push VS grow

问题:

What is the difference between these two constraints?

From documentation:

PUSH - makes the row and/or column that the component is residing in grow with "weight"

GROW - Sets how keen the component should be to grow in relation to other component in the same cell.

So, the main idea is to shrink size inside and outside of component?

回答1:

It is important to understand that fill, (column, row) grow, push work in conjunction with the (component) grow to define the layout. (There are two different grow constraints that do different things.)

MigLayout is a grid-based manager. (More precisely, its most important mode is.) There are two steps that need to be done:

• define how much space the columns and rows of the grid take
• define how much space components occupy in their alotted cell(s)

This is what fill, (column, row) grow, push and (component) grow constraints help achieve. The first three define the growth of the grid's columns and rows, the last one defines how the component will spread over its alotted area, e.g. cell(s) that it is placed in. Note that filling or growing is the tendency or eagerness to occupy empty space in the layout. The window area that is not taken by columns, rows, or components is filled with empty space.

The push and the (column, row) grow take optional weight parameter. It defines how keen the column or row should grow in relation to other columns and rows. The fill constraint distributes the weight evenly.

(The push constraint may be used to make gaps greedy in different context.)

I provide three examples that clarify usage of these constraints.

Fill

The fill constraint affects all cells of the grid. They occupy all available space. The (component) grow constraint specifies how the components spread in their cells.

package com.zetcode;

import java.awt.EventQueue;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import net.miginfocom.swing.MigLayout;


public class MigLayoutFillEx extends JFrame {

    public MigLayoutFillEx() {

        initUI();

        setSize(300, 250);
        setTitle("Fill");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    private void initUI() {

        JPanel pnl = new JPanel(new MigLayout("fill"));

        pnl.add(getLabel("Area 1"), "cell 0 0, growx");
        pnl.add(getLabel("Area 2"), "cell 0 1, grow");
        pnl.add(getLabel("Area 3"), "cell 1 0 1 2, grow");

        add(pnl);
    }

    private JLabel getLabel(String text) {

        JLabel label = new JLabel(text, JLabel.CENTER);
        label.setBorder(BorderFactory.createEtchedBorder());

        return label;
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                MigLayoutFillEx ex = new MigLayoutFillEx();
                ex.setVisible(true);
            }
        });
    }
}

In the example we have three labels.

JPanel pnl = new JPanel(new MigLayout("fill"));

The fill is a layout constraint; it affects all cells.

pnl.add(getLabel("Area 1"), "cell 0 0, growx");
pnl.add(getLabel("Area 2"), "cell 0 1, grow");
pnl.add(getLabel("Area 3"), "cell 1 0 1 2, grow");

Now we define how the components fill their areas alotted by the layout manager. The Area 1 label fills its alotted area horizontally, the other two labels fill the alotted area in both dimensions.

Column, row grow

The (column, row) grow constraint affects all cells in particular column or row.

package com.zetcode;

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import net.miginfocom.swing.MigLayout;


public class MigLayoutGrowEx extends JFrame {

    public MigLayoutGrowEx() {

        initUI();

        setSize(300, 250);
        setTitle("Grow constraint");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    private void initUI() {

        JPanel pnl = new JPanel(new MigLayout("wrap", "[grow]", "[][grow]"));

        JTextField field = new JTextField(10);
        JTextArea area = new JTextArea(10, 10);

        pnl.add(field, "growx");
        pnl.add(new JScrollPane(area), "grow");

        add(pnl);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                MigLayoutGrowEx ex = new MigLayoutGrowEx();
                ex.setVisible(true);
            }
        });
    }
}

In the example we have two components. The text field is expected to grow horizontally, the text area both horizontally and vertically.

JPanel pnl = new JPanel(new MigLayout("wrap", "[grow]", "[][grow]"));

In this line we specify that the first colum and the second row of the grid grow.

pnl.add(field, "growx");
pnl.add(new JScrollPane(area), "grow");

Now we define that the text field fills its alotted area horizontally while the text area fills the whole alotted area.

Push

The push constraint is esentially the same as the (column, row) grow. The difference is that push is specified at the add() method.

package com.zetcode;

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import net.miginfocom.swing.MigLayout;


public class MigLayoutPushEx extends JFrame {

    public MigLayoutPushEx() {

        initUI();

        setSize(300, 250);
        setTitle("Push constraint");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    private void initUI() {

        JPanel pnl = new JPanel(new MigLayout("wrap"));

        JTextField field = new JTextField(10);
        JTextArea area = new JTextArea(10, 10);        

        pnl.add(field, "pushx, growx");
        pnl.add(new JScrollPane(area), "push, grow");

        add(pnl);
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                MigLayoutPushEx ex = new MigLayoutPushEx();
                ex.setVisible(true);
            }
        });
    }
}

The example is the same as the previous one.

JPanel pnl = new JPanel(new MigLayout("wrap"));

No growing is specified here.

pnl.add(field, "pushx, growx");
pnl.add(new JScrollPane(area), "push, grow");

Everything is specified using components' constraints within the add() methods.