JTree with checkboxes

Question

I need to add checkboxes to a JTree. A custom TreeCellRenderer/TreeCellEditor seems like the right approach. So far I used the CheckBoxNodeRenderer approach in this webpage.

Answer 1

I know this question has been answered already, but i just want to clear some points:

1) JIDE Common Layer is dual-licensed (GPL with classpath exception and free commercial license). This means that you can use the Common Layer Project without any licensing issues. Please check the following link to confirm: http://www.jidesoft.com/products/oss.htm. The Common Layer includes an implementation of a checkable JTree (com.jidesoft.swing.CheckBoxTree).

2) There's a blog dated from 2005 from the Master himself, Santhosh Kumar, where he explains how to implement a JTree with checkboxes with the requirements you mentioned: http://www.jroller.com/santhosh/entry/jtree_with_checkboxes. It's worth reading it, in my opinion.

Answer 2

As for #2, you could make a panel be the editor/renderer, and add a label along with the checkbox - the label would be the text, and the check box would not have the text added to it.

Answer 3

per @aperkins suggestion this is what I ended up doing in the TableCellRenderer, it seems to work well:

final private JPanel nodeRenderer = new JPanel();
final private JLabel label = new JLabel();
final private JCheckBox check = new JCheckBox();

     ...

// in constructor:
final Insets inset0=new Insets(0,0,0,0);        
this.check.setMargin(inset0);
this.nodeRenderer.setLayout(new BorderLayout()); 
this.nodeRenderer.add(this.check, BorderLayout.WEST);
this.nodeRenderer.add(this.label, BorderLayout.CENTER);

The keys for getting rid of unwanted space in the margins seems to be (a) calling JCheckBox.setMargin() to reduce the checkbox margin, and (b) using a BorderLayout for JPanel.

Answer 4

I have released a standalone Swing Checkbox Tree project, available from Maven Central as org.scijava:swing-checkbox-tree.

The package is based on John Zukowski's CheckBox Node Tree Sample code. It is BSD-2-licensed with no dependencies.

It allows mixing and matching of DefaultMutableTreeNode and CheckBoxNodeData node types. It also allows check box nodes as non-leaf nodes.

Regarding the question's issue #1: I did not test on all platforms, but on my OS X systems, the CheckBoxNodeData nodes are exactly the same height in pixels as the DefaultMutableTreeNode nodes.

Regarding the question's issue #2: it uses a JCheckBox + JLabel in a JPanel (as aperkins suggests) to differentiate between clicking on a check box (to check/uncheck a node) versus a label (to select a node).

Example usages:

• Simple: CheckBoxTreeSample
• Complex: WatchEventsFrame

The latter example also has code for recursively toggling subtrees in response to boxes being checked or unchecked (see the treeNodesChanged method).