Check for wrapped elements in JavaFX-FlowPane

Question

Is there an easy way to check for wrapped elements inside a FlowPane or determine the index at which the elements are wrapped?

Answer 1

I don't know if it qualifies as "easy", but you can check the boundsInParent for each child and compare it to the first child. For a horizontal FlowPane this should work:

private List<Node> findWrapped(FlowPane flow) {
    List<Node> wrapped = new ArrayList<>();
    if (flow.getChildren().size() == 0) {
        return wrapped ;
    }
    double y = flow.getChildren().get(0).getBoundsInParent().getMaxY();
    for (Node child : flow.getChildren()) {
        if (child.getBoundsInParent().getMinY() >= y) {
            wrapped.add(child);
        }
    }
    return wrapped ;
}

SSCCE:

import java.util.ArrayList;
import java.util.List;

import javafx.application.Application;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.FlowPane;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class FlowPaneWrappedNodes extends Application {


    @Override
    public void start(Stage primaryStage) {
        FlowPane flow = new FlowPane();
        for (int i = 1 ; i <= 15; i++) {
            flow.getChildren().add(createPane(i));
        }
        Button button = new Button("Find wrapped");
        button.setOnAction(e ->
                findWrapped(flow).stream().map(Node::getId).forEach(System.out::println));
        BorderPane root = new BorderPane(flow, null, null, button, null);
        Scene scene = new Scene(root, 600, 600);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private List<Node> findWrapped(FlowPane flow) {
        List<Node> wrapped = new ArrayList<>();
        if (flow.getChildren().size() == 0) {
            return wrapped ;
        }
        double y = flow.getChildren().get(0).getBoundsInParent().getMaxY();
        for (Node child : flow.getChildren()) {
            if (child.getBoundsInParent().getMinY() >= y) {
                wrapped.add(child);
            }
        }
        return wrapped ;
    }

    private Pane createPane(int id) {
        Pane pane = new StackPane();
        pane.setMinSize(50, 50);
        pane.setId("Pane "+id);

        Label label = new Label(Integer.toString(id));
        pane.getChildren().add(label);

        return pane ;
    }

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

For a vertical flow pane, you can do something similar, comparing the x values of the bounds instead of the y.

Update:

Making this recompute automatically is a bit tricky. You basically need to observe the child list of the FlowPane (in case new nodes are added or removed), and then observe the bounds of each node in the flow pane. You can do this with code like this:

    FlowPane flow = new FlowPane();

    ListView<Node> wrappedNodeView = new ListView<>();

    ChangeListener<Bounds> boundsListener = (obs, oldBounds, newBounds) -> 
        wrappedNodeView.getItems().setAll(findWrapped(flow));

    flow.getChildren().addListener((Change<? extends Node> c) -> {
        while (c.next()) {
            if (c.wasAdded()) {
                c.getAddedSubList().forEach(node -> node.boundsInParentProperty().addListener(boundsListener));
            }
            if (c.wasRemoved()) {
                c.getRemoved().forEach(node -> node.boundsInParentProperty().removeListener(boundsListener));
            }
        }
        wrappedNodeView.getItems().setAll(findWrapped(flow));           
    });

(This creates a list view which displays all the "wrapped" nodes. You can obviously just update a list or whatever as you need.)

Here it is built into the previous SSCCE:

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.collections.FXCollections;
import javafx.collections.ListChangeListener.Change;
import javafx.collections.ObservableList;
import javafx.geometry.Bounds;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.FlowPane;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class FlowPaneWrappedNodes extends Application {


    @Override
    public void start(Stage primaryStage) {
        FlowPane flow = new FlowPane();

        ListView<Node> wrappedNodeView = new ListView<>();

        ChangeListener<Bounds> boundsListener = (obs, oldBounds, newBounds) -> 
            wrappedNodeView.getItems().setAll(findWrapped(flow));

        flow.getChildren().addListener((Change<? extends Node> c) -> {
            while (c.next()) {
                if (c.wasAdded()) {
                    c.getAddedSubList().forEach(node -> node.boundsInParentProperty().addListener(boundsListener));
                }
                if (c.wasRemoved()) {
                    c.getRemoved().forEach(node -> node.boundsInParentProperty().removeListener(boundsListener));
                }
            }
            wrappedNodeView.getItems().setAll(findWrapped(flow));           
        });

        wrappedNodeView.setCellFactory(lv -> new ListCell<Node>() {
            @Override
            public void updateItem(Node item, boolean empty) {
                super.updateItem(item, empty);
                if (empty) {
                    setText("");
                } else {
                    setText(item.getId());
                }
            }
        });

        Button button = new Button("Add pane");
        button.setOnAction(e ->
                flow.getChildren().add(createPane(flow.getChildren().size()+1)));

        BorderPane root = new BorderPane(flow, null, wrappedNodeView, button, null);
        Scene scene = new Scene(root, 600, 600);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private ObservableList<Node> findWrapped(FlowPane flow) {
        ObservableList<Node> wrapped = FXCollections.observableArrayList();
        if (flow.getChildren().size() == 0) {
            return wrapped ;
        }
        double y = flow.getChildren().get(0).getBoundsInParent().getMaxY();
        for (Node child : flow.getChildren()) {
            if (child.getBoundsInParent().getMinY() >= y) {
                wrapped.add(child);
            } 
        }
        return wrapped ;
    }

    private Pane createPane(int id) {
        Pane pane = new StackPane();
        pane.setMinSize(50, 50);
        pane.setId("Pane "+id);

        Label label = new Label(Integer.toString(id));
        pane.getChildren().add(label);

        return pane ;
    }

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