Question

I have a tree with DefaultMutableTreeNodes only. I want to write a TreeCellRenderer that depends on the type of the contained user object. I tried to write a simple example (which doesn’t work. That’s why I ended up here). On the first level beyond the root node, the types of the user objects are either AANodeUserObjector LocalAANodeUserObject. Both should be rendered with directory icons even though there might be no child. The other feature of this renderer is, that it should render nodes with user object type AANodeUserObject in red color and bold when they are not “current” (in my example, this is always true). Here is my code:

    public Component getTreeCellRendererComponent(final JTree tree, final Object value, final boolean sel, final boolean expanded, final boolean leaf, final int row, final boolean hasFocus)
    {
        super.getTreeCellRendererComponent(tree, value, sel, expanded, leaf, row, hasFocus);
        // Precondition für Default TreeNode
        Object userObject = ((DefaultMutableTreeNode) value).getUserObject();
        if (userObject instanceof TestTree.AANodeUserObject || userObject instanceof TestTree.LocalAANodeUserObject)
        {
            if (expanded)
            {
                setIcon(openIcon);
            }
            else
            {
                setIcon(closedIcon);
            }
        }

        if (userObject instanceof TestTree.AANodeUserObject)
        {
            TestTree.AANodeUserObject aAnode = (TestTree.AANodeUserObject) userObject;
            if (!mVersionInfo.get(aAnode))
            {
                renderOutdatedAaNode();
            } else {
                renderDefault();
            }
        }  else {
            renderDefault();
        }
        return this;
    }

    private void renderDefault()
    {
        setTextNonSelectionColor(cColorBlack);
        setTextSelectionColor(cColorBlack);
        setFont(getFont().deriveFont(Font.PLAIN));
    }

    private void renderOutdatedAaNode()
    {
        setTextNonSelectionColor(cColorRed);
        setTextSelectionColor(cColorRed);
        setFont(getFont().deriveFont(Font.BOLD));
    }

You can see the result on the attached picture.

What irritates me is that the directory-icon-thing works fine, the text style doesn’t: only the second node (Hashmap value is false) AANodeUserObject should be red and nothing else.
What am I doing wrong? Can somebody help?
Thanks!
Mathias

Answer 1

I solved the problems by calling super.getTreeCellRendererComponent(tree, value, sel, expanded, leaf, row, hasFocus) twice:

• The first time as first line of getTreeCellRendererComponent(). Without the call, getFont(setFont()) to set the font style to bold will return a NullPointerException.

• The second time at the last line in the method to render the nodes properly.

There might be another solution but after many different tries, this has worked for me.