java - 为什么 JTree 仅在创建 JTree 之前填充关联的 DefaultTreeModel 时才显示数据？

Question

我在名为 TreeFrame 的 JFrame 子类的构造函数中包含此代码。我想在 JTree 中显示 3 个级别，每个级别 10 个项目。为什么这会按预期工作:

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 ROOT 节点之外，这没有显示任何内容？我只将最后一条指令 tree = new JTree(treeModel); 移到循环 block 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() 放入 EDT 线程有关？

Answer 1

两种方法都可以很好地构建模型，并且所有数据都在那里，问题出在第二个示例中，默认情况下根节点是折叠的。

完成模型构建后，尝试添加tree.expandPath(new TreePath(r));。