用treeview显示目录及其子目录和文件，同时可以查看文件文件内容

val mutableMap = mutableMapOf<String,String>()
class TreeviewDemo:Fragment(){
    var tv=TreeView<String>()
    var nodes=TreeItem<String>()
    val fname= stringProperty()
    val content= stringProperty()

    override val root =vbox {
        button("load tree") {
            action {
                val d=chooseDirectory{}
//                println(d!!.absoluteFile)
                runAsync{
                     nodes=getNodesForDirectory(d!!.absoluteFile)
                }ui {
                    tv.root=nodes
                }
            }
        }
        hbox {
            tv=treeview<String> {
                root=TreeItem("")
                bindSelected(fname)
                selectionModel.selectedItemProperty().addListener { _ ->
                    val fpath=mutableMap.get(selectionModel.selectedItem!!.value)
                    content.value=File(fpath).readText()
                }
            }
            textarea(content) {

            }
        }
    }

}
//Returns a TreeItem representation of the specified directory
tailrec fun getNodesForDirectory(directory: File): TreeItem<String> {
    val root = TreeItem<String>(directory.getName())
    directory.listFiles().forEach {
        if (it.isDirectory()) { //Then we call the function recursively
            root.children.add(getNodesForDirectory(it))
        } else {
            root.children.add(TreeItem<String>(it.getName()))
        }
        mutableMap.put(it.name,it.absolutePath)
    }
    return root
}