JPanel inside a JScrollPane

Question

I have a JPanel and I create, dynamically, JCheckBoxes inside. These have to be added JCheckBoxes always a side by side. In case there is more space to be inserted in the side, a new line of JCheckBoxes is created, as in a simple text editor.

This is happening perfectly. But ...

I set the layout on this JPanel to FlowLayout, exactly what I want.

The obvious problem is that a window has limited space. So a good solution to this is: Insertion of this JPanel in a JScrollPane,l and making that happen only in the vertical scrolling. But I have problems. Although you can make only a vertical scroll bar to appear, the items are always added "forever" side by side. And the vertical scroll simply does not work, only horizontally.

I've tried many ways to make the scroll only vertically, but nothing worked (if it had worked I would not be here:]).

So, has anyone had any similar problem, and can help me?

I shall be very grateful to those who help me.

No more.

Answer 1

I dealt with the same issue with ScrollPanes and FlowLayouts. I found the best solution is to use a modified version of FlowLayout that takes into account vertical changes. Here is the code for such a layout. You can include it in your project and call it just like a FlowLayout, however it will actually work nice with a scrollpane.

import java.awt.*;

/**
  * A modified version of FlowLayout that allows containers using this
  * Layout to behave in a reasonable manner when placed inside a
  * JScrollPane

  * @author Babu Kalakrishnan
  * Modifications by greearb and jzd
  */

 public class ModifiedFlowLayout extends FlowLayout {
       public ModifiedFlowLayout() {
              super();
           }

           public ModifiedFlowLayout(int align) {
              super(align);
           }
       public ModifiedFlowLayout(int align, int hgap, int vgap) {
          super(align, hgap, vgap);
       }

       public Dimension minimumLayoutSize(Container target) {
          // Size of largest component, so we can resize it in
          // either direction with something like a split-pane.
          return computeMinSize(target);
       }

       public Dimension preferredLayoutSize(Container target) {
          return computeSize(target);
       }

       private Dimension computeSize(Container target) {
          synchronized (target.getTreeLock()) {
             int hgap = getHgap();
             int vgap = getVgap();
             int w = target.getWidth();

             // Let this behave like a regular FlowLayout (single row)
             // if the container hasn't been assigned any size yet
             if (w == 0) {
                w = Integer.MAX_VALUE;
             }

             Insets insets = target.getInsets();
             if (insets == null){
                insets = new Insets(0, 0, 0, 0);
             }
             int reqdWidth = 0;

             int maxwidth = w - (insets.left + insets.right + hgap * 2);
             int n = target.getComponentCount();
             int x = 0;
             int y = insets.top + vgap; // FlowLayout starts by adding vgap, so do that here too.
             int rowHeight = 0;

             for (int i = 0; i < n; i++) {
                Component c = target.getComponent(i);
                if (c.isVisible()) {
                   Dimension d = c.getPreferredSize();
                   if ((x == 0) || ((x + d.width) <= maxwidth)) {
                      // fits in current row.
                      if (x > 0) {
                         x += hgap;
                      }
                      x += d.width;
                      rowHeight = Math.max(rowHeight, d.height);
                   }
                   else {
                      // Start of new row
                      x = d.width;
                      y += vgap + rowHeight;
                      rowHeight = d.height;
                   }
                   reqdWidth = Math.max(reqdWidth, x);
                }
             }
             y += rowHeight;
             y += insets.bottom;
             return new Dimension(reqdWidth+insets.left+insets.right, y);
          }
       }

       private Dimension computeMinSize(Container target) {
          synchronized (target.getTreeLock()) {
             int minx = Integer.MAX_VALUE;
             int miny = Integer.MIN_VALUE;
             boolean found_one = false;
             int n = target.getComponentCount();

             for (int i = 0; i < n; i++) {
                Component c = target.getComponent(i);
                if (c.isVisible()) {
                   found_one = true;
                   Dimension d = c.getPreferredSize();
                   minx = Math.min(minx, d.width);
                   miny = Math.min(miny, d.height);
                }
             }
             if (found_one) {
                return new Dimension(minx, miny);
             }
             return new Dimension(0, 0);
          }
       }

    }