Unexpected guard block: Unable to add element

[ennerf]

I keep running into this guard block SceneGraphTree.java#L349-L353 that should supposedly never happen.

Juli 24, 2025 3:20:06 PM devtoolsfx.connector.LocalConnector start
INFO: LocalConnector started
Juli 24, 2025 3:20:06 PM devtoolsfx.connector.BoundsPane attach
WARNING: Could not find writable parent to add overlay nodes, overlay is disabled
Juli 24, 2025 3:20:06 PM devtoolsfx.connector.LocalConnector handleWindowAdd
SEVERE: Attempting to add a new window that already has a bound monitor object
Juli 24, 2025 3:20:06 PM devtoolsfx.connector.BoundsPane attach
WARNING: Could not find writable parent to add overlay nodes, overlay is disabled
Juli 24, 2025 3:20:06 PM devtoolsfx.connector.BoundsPane attach
WARNING: Could not find writable parent to add overlay nodes, overlay is disabled
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present
Juli 24, 2025 3:20:06 PM devtoolsfx.gui.inspector.SceneGraphTree doAddElement
WARNING: Unable to add element as it is already present

I don't know what exactly is causing it, but it looks like something related to chart-fx. A minimum sample is

<dependency>
    <groupId>io.github.mkpaz</groupId>
    <artifactId>devtoolsfx-gui</artifactId>
    <version>1.0.1</version>
</dependency>
<dependency>
    <groupId>io.fair-acc</groupId>
    <artifactId>chartfx</artifactId>
    <version>11.3.1</version>
</dependency>

import devtoolsfx.gui.GUI;
import io.fair_acc.chartfx.XYChart;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class MinimalSample extends Application {

    @Override
    public void start(Stage stage) throws Exception {
        GUI.openToolStage(stage, getHostServices());
        var root = new XYChart();
        stage.setScene(new Scene(root));
        stage.show();
    }

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

}

[mkpaz]

The issue is caused by an unexpected/invalid code flow. The way devtools works is by attaching a connector to the monitored app's primary stage, which should happen strictly after the primary stage is shown.

primaryStage.setOnShown(e -> GUI.openToolStage(primaryStage, getHostServices()));

Calling openToolStage before the primary stage is ready leads to this type of issues, because JavaFX switches sceneProperty() several times.

I will leave this open as a reminder that devtools should investigate a way to defer UI changes until the primary stage is shown if it wasn't started in a setOnShown() callback.