Select first item shown into a treeTableView in JavaFX 8

Question

I have a TreeTableView control with several items. The user can move with the side scroll bar to any part of the table. How can I know which is the first item that the table shows? I mean, the first item we see. I have been going through the methods offered by this control and I have seen that scrollTo shows an item according to an order number that we specify but I have not found anything that is something like getFirstItemShown. I imagine that for a TableView control it should work the same, right? I'm using JavaFX 8.

Answer 1

Just for fun:

(note that if there are cut lines it can choose the next row, and the first row is sometimes hidden under the Column)

import javafx.application.Application;
import javafx.application.Platform;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.stage.Stage;
import javafx.beans.property.ReadOnlyStringWrapper;
import javafx.scene.control.TreeTableColumn;
import javafx.scene.control.TreeTableColumn.CellDataFeatures;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeTableView;


public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{

        primaryStage.setTitle("Tree View Sample");
        TreeItem<String> rootItem = new TreeItem<String> ("Inbox");
        rootItem.setExpanded(true);

        for (int i = 1; i < 888; i++) {
            TreeItem<String> item = new TreeItem<String> ("Message" + i);
            rootItem.getChildren().add(item);
        }
        TreeTableColumn<String, String> column = new TreeTableColumn<>("Column");
        column.setPrefWidth(150);
        column.setCellValueFactory((CellDataFeatures<String, String> p) -> new ReadOnlyStringWrapper(
                p.getValue().getValue()));
        TreeTableView<String> treeTableView = new TreeTableView<>(rootItem);
        treeTableView.getColumns().add(column);
        primaryStage.setScene(new Scene(treeTableView, 300, 250));
        primaryStage.show();

        Platform.runLater(()->{
            ScrollBar verticalBar = (ScrollBar) treeTableView.lookup(".scroll-bar");
            verticalBar.valueProperty().addListener(new ChangeListener<Number>() {
                @Override
                public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
                    int currentRow = 0;
                    if(newValue.doubleValue()<1){
                        currentRow =(int)((newValue.doubleValue()*treeTableView.getExpandedItemCount())-(newValue.doubleValue()*verticalBar.getVisibleAmount())*treeTableView.getExpandedItemCount());
                    }else {
                        currentRow =(int)(treeTableView.getExpandedItemCount()-verticalBar.getVisibleAmount()*treeTableView.getExpandedItemCount());
                    }
                    System.out.println(currentRow);
                }
            });
        });
    }

    public static void main(String[] args) {
        launch(args);
    }
}