Core JFC Java Foundation Classes 2nd edition - Read

1266 Chapter 10 The Tree Control
Node-specific Tooltips Using a Custom Renderer
A third approach to the problem, and the most powerful, is to implement
tooltip support in the renderer. This makes it possible to return a different
tooltip for each node if necessaiy. As we said in the previous section, JTree
overrides the getToolTipText method to get the tooltip for each node
from that node's renderer. It does this by calling the Tenderer's getTree-
CellRendererComponent method as if it were going to render the node
and then invokes the getToolTipText method of the returned component
to get the tooltip for the node. If you want your nodes to display tooltips, you
simply have to call set Tool TipText on the component that you return
from the Tenderer's getTreeCellRendererComponent method.
To demonstrate the general technique, we'll modify the custom renderer
shown in Listing 10-6 to include a tooltip. For simplicity, we'll make the tooltip
be the same text as would be displayed on the node itself. In a real-world
application, you would probably store the tooltip as part of the node or its
user object and code the renderer to extract it from there. Setting the tooltip
requires only one extra line of code in the renderer's getTreeCellRendererComponent
method:
// By default, use the same value as the
// node text for the tooltip, for leaf nodes only
((JComponent)c).setToolTipText(
leaf ? value.toString() : null);
where the variable c is the component being returned by the renderer. In
this example, we set a tooltip only for leaf nodes.
Having made this change, you just need to register the tree with the Tool-
TipManager, as shown earlier in this section, and your tree will display a different
tooltip for each leaf node. However, as with the first approach we took
to displaying tooltips, a tooltip will only be displayed when the mouse is over
an area that will be drawn by a renderer. To arrange for a tooltip to be displayed
wherever the mouse is, we can combine this approach with the previous
one by subclassing JTree and implementing a cleverer version of
getToolTipText:
public String getToolTipText(MouseEvent evt) {
// Let the renderer supply the tooltip
String tip = super.getToolTipText(evt);
}
// If it did not, return the tree's tip
return tip != null ? tip : getToolTipText();