为什么只有在创建JTree之前填充了关联的DefaultTreeModel，JTree才会显示数据？

Question

我在一个名为TreeFrame的JFrame的子类的构造函数中有这段代码。我想在JTree中显示3个级别，每个级别10个项目。为什么它会像预期的那样工作：

private DefaultTreeModel treeModel;
private DefaultMutableTreeNode r;
private JTree tree;
...
r = new DefaultMutableTreeNode("ROOT");
treeModel = new DefaultTreeModel(r);

for (int i = 0; i < 10; i++) {
    String a = "Object " + i;
    DefaultMutableTreeNode aNode = new DefaultMutableTreeNode(a);
    treeModel.insertNodeInto(aNode, r, r.getChildCount());
    for (int j = 0; j < 10; j++) {
        String b1 = "Sub-Object " + j;
        DefaultMutableTreeNode bNode = new DefaultMutableTreeNode(b1);
        treeModel.insertNodeInto(bNode, aNode, aNode.getChildCount());
        for (int k = 0; k < 10; k++) {
            String c = "Sub-Sub-Object " + k;
            treeModel.insertNodeInto(new DefaultMutableTreeNode(c),
                    bNode, bNode.getChildCount());
        }
    }
}

tree = new JTree(treeModel);

除了根节点，这不会显示任何内容？我只将最后一条指令tree = new JTree(treeModel);移到了周期块之前。

private DefaultTreeModel treeModel;
private DefaultMutableTreeNode r;
private JTree tree;
...
r = new DefaultMutableTreeNode("ROOT");
treeModel = new DefaultTreeModel(r);
tree = new JTree(treeModel);

for (int i = 0; i < 10; i++) {
    String a = "Object " + i;
    DefaultMutableTreeNode aNode = new DefaultMutableTreeNode(a);
    treeModel.insertNodeInto(aNode, r, r.getChildCount());
    for (int j = 0; j < 10; j++) {
        String b1 = "Sub-Object " + j;
        DefaultMutableTreeNode bNode = new DefaultMutableTreeNode(b1);
        treeModel.insertNodeInto(bNode, aNode, aNode.getChildCount());
        for (int k = 0; k < 10; k++) {
            String c = "Sub-Sub-Object " + k;
            treeModel.insertNodeInto(new DefaultMutableTreeNode(c),
                    bNode, bNode.getChildCount());
        }
    }
}

也许这与没有将new TreeFrame()放在EDT线程中有关？

Answer 1

这两种方法都很好地构建了模型，所有数据都在那里，问题是在第二个示例中，默认情况下根节点是折叠的。

在构建完模型之后，尝试添加tree.expandPath(new TreePath(r));。