JavaFx：当Treeitem不在视图中时，在TreeView中仅需要滚动到索引号

Question

I need to do a simple thing. I have a large TreeView. and a menu item Next and Previous. on Next I have to select next Tree Item. Tree List Look like this

-Root(set visible hide is true for root)
 --Parent 1
 ----Child 1
 ----Child 2
 ----Child 3
 --Parent 2
 ----Child 1
 ----Child 2

Now By pressing Next or previous menu item i call

myTreeView.getSelectionModel().clearAndSelect(newIndex);

By This I have manage to select next item and by

myTreeView.getSelectionModel().scrollTo(newIndex) 

i have manage to scroll to selected treeitem.

Problam:

Let I select the first item manually. after this i press next button. Now This cause a weird behavior that it always scrolls weather new selected treeitem is in view (bounds of view able area) or out of view. let assume i have large list of tree items. and my requirement is just i only want scroll happened only when new selected tree item go out of view. can any body suggest how to achieve this??

Thanks.

Answer 1

This simple thing is not so simple. It is a known issue in JavaFX; see issue RT-18965 .

Based on the comment in the issue, I have made it work with my own TreeView. Please note that - as in the issue comment - I have relied on internal classes within JavaFX to get my end result. There is no guarantee that these internal classes will continue to be.

First, create a new Skin that is derived from an internal class (again: dangerous):

import javafx.scene.control.TreeView;
import com.sun.javafx.scene.control.skin.TreeViewSkin;
import com.mycompany.mymodel.DataNode;

/**
 * Only done as a workaround until https://javafx-jira.kenai.com/browse/RT-18965
 * is resolved.
 */
public class FolderTreeViewSkin extends TreeViewSkin<DataNode>
{
    public FolderTreeViewSkin(TreeView<DataNode> treeView)
    {
        super(treeView);
    }

    public boolean isIndexVisible(int index)
    {
        if (flow.getFirstVisibleCell() != null &&
            flow.getLastVisibleCell() != null &&
            flow.getFirstVisibleCell().getIndex() <= index &&
            flow.getLastVisibleCell().getIndex() >= index)
            return true;
        return false;
    }
}

Second, apply that skin to the TreeView instance you are concerned about.

myTreeView.setSkin(new FolderTreeViewSkin(myTreeView));

Finally, use the new method as a condition before scrollTo :

if (!((FolderTreeViewSkin) myTreeView.getSkin()).isIndexVisible( intThePositionToShow ))
    myTreeView.scrollTo( intThePositionToShow );

This is what worked for me; I hope it can help you or anyone else.