Why my JTree always collasped after refreshing?

Question

Hello,
I have been spending whole day trying to figure out why my JTree always collasped after refreshing, but I haven't got any fruit.
I have a Tree and it is collasped in the beginning, and I can expand and do some work(adding nodes or deleting nodes - no problem)
But there is a button which validates the tree, and if a node has problem, its background changes which part is working Okay.
but the tree always goes back to collasped(original state)
I tried every methods that I searched, but nothing is working.
Below is the codes..
private void validateManifest() {
            CP_EditorHandler.checkManifestErrors(_contentPackage, false);
        ManifestTree manifestTree = _manifestPanel.getManifestTree();
     // get the selected node before updating
        ManifestTreeNode selectedNode = (ManifestTreeNode) manifestTree.getSelectedNode();
     // get the selected path before updating
        TreePath selectedPath = (TreePath) manifestTree.getSelectionPath();
     // below code is the part that recreates nodes of the tree and updates nodes' background
        manifestTree.getModel().setContentPackage(_contentPackage);
     // I set below code to expand to selected path
        manifestTree.setExpandsSelectedPaths(true);
     // I even added this code to make it sure
        manifestTree.setExpandedState(selectedPath, true);
}I even added addTreeWillExpandListener in the tree constructor, but it doesn't work either.
         addTreeWillExpandListener
         (new TreeWillExpandListener() {
           public void treeWillExpand(TreeExpansionEvent e) { }
           public void treeWillCollapse(TreeExpansionEvent e)
                throws ExpandVetoException {
            throw new ExpandVetoException(e, "you can't collapse this JTree");
           });What did I do wrong or what should I do to make it work?
I really appreciate your help.

Answer 1

I have been spending whole day trying to figure out why...no, you've spent your day cross-posting this.
I don't know where to post the solution, l so I won't bother.