JScrollPane not working in null layout

Question

  import javax.swing.JCheckBox;
  import javax.swing.JFrame;
  import javax.swing.JLabel;
  import javax.swing.JPanel;
  import javax.swing.JScrollPane;

public class Sc         


        

Answer 1

I see OP already set desired/correct answer for him, yet that solution does not work with dynamic content (in my case vertically on Y axis) so I "repaired" or updated - if you will - Mateusz's original answer so that now it actually works even with dynamic JPanel content (like when you adding to it other components on the run which was my case).

Here is my code (works, using it myself):

import java.awt.Component;
import java.awt.Dimension;

import javax.swing.JPanel;

public class JPanelForNullLayoutScroll extends JPanel {

    int h;

    @Override
    public Dimension getPreferredSize() {

        if (getComponentCount() > 0) {
            h = 0;

            for (Component c : getComponents()) {
                h += c.getHeight();
            }

        } else {
            h = 0;
        }

        // as I do not need width recount
        //I set it to be taken directly from the component itself
        Dimension d = new Dimension(getWidth(), h);

        return d;
    }

}

You can use it then in your code by implementing it like:

int tableW = 300;
int tableH = 300;

// JPANEL WITH NULL LAYOUT
JPanelForNullLayoutScroll container = new JPanelForNullLayoutScroll();
container.setLayout(null);
container.setVisible(true);
container.setEnabled(true);
container.setBounds(0, 0, tableW, tableH);

// SCROLLER
JScrollPane scrollPane = new JScrollPane(container);
scrollPane.setAlignmentX(JLabel.LEFT_ALIGNMENT);
scrollPane.getVerticalScrollBar().setUnitIncrement(8);
scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
scrollPane.setBounds(0, 0, tableW, tableH);

Answer 2

You should create your own panel that extends JPanel containing all checkboxes and in this panel override getPreferredSize() method like:

@Override
public Dimension getPreferredSize()
{
    return new Dimension( 300,300 );
}

and use it in your code:

...

// creating the scroll pane that will scroll the panel.
JScrollPane jscrlPane = new JScrollPane( new MyPanelWithCheckboxes() );
jscrlPane.setBounds( 0, 0, 300, 300 );
...