Swing Hacks

Animate JTree Drops #27

Chapter 3, Tables and Trees

|

145

HACK

The special rendering is a two-step process. First, getTreeCellRendererComponent( )

figures out if the cell to be rendered is the drop target, and if so, it sets a

local

boolean

. It sets another

boolean

to indicate that the drop target cell is a

leaf. Having set these

boolean

s, it returns the superclass’s implementation.

In short order, the renderer’s

paint( )

method is called. In the

paint( )

, you

can use the

boolean

s to apply special rendering. In this version, a drop tar-

get that is a leaf gets a line drawn in its top inset, suggesting that the

dropped item will be inserted before this node. If rendering a drop target

that is a branch—i.e., it’s not a leaf—then the special rendering puts a box

around the component.

Running the Code

The main method, shown in Example 3-17, builds a reorderable tree and

puts it in a

JFrame.

Example 3-17. Testing the drag-and-drop JTree

public static void main (String[] args) {

JTree tree = new DnDJTree( );

DefaultMutableTreeNode root = new DefaultMutableTreeNode("People");

DefaultMutableTreeNode set1 = new DefaultMutableTreeNode("Set 1");

DefaultMutableTreeNode set2 = new DefaultMutableTreeNode("Set 2");

DefaultMutableTreeNode set3 = new DefaultMutableTreeNode("Set 3");

set1.add (new DefaultMutableTreeNode ("Chris"));

set1.add (new DefaultMutableTreeNode ("Kelly"));

set1.add (new DefaultMutableTreeNode ("Keagan")); ...