Putting an object on a stage when mouse clicked

问题

package javafxapplication36;

/**
 * Copyright (c) 2008, 2012 Oracle and/or its affiliates.
 * All rights reserved. Use is subject to license terms.
 */
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.stage.Stage;
import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.animation.Timeline;
import javafx.beans.InvalidationListener;
import javafx.beans.Observable;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.VPos;
import javafx.scene.Group;
import javafx.scene.Node;
import javafx.scene.control.Button;
import javafx.scene.effect.DropShadow;
import javafx.scene.effect.Lighting;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Text;
import javafx.scene.text.TextAlignment;
import javafx.util.Duration;

/**
 * A sample that demonstrates how to add or remove a change listener on a node
 * (for example, a Rectangle node) for some property (for example,
 * Rectangle.hover). Once you add a listener, the text field  shows the hover
 * property change.
 *
 * @see javafx.beans.value.ChangeListener
 * @see javafx.beans.InvalidationListener
 * @see javafx.beans.value.ObservableValue
 */
public class ChangeListenerSample extends Application {

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

    private void init(Stage primaryStage) {
        final Group root = new Group();
        primaryStage.setResizable(false);
        Scene scene = new Scene(root, 400,80);
        primaryStage.setScene(scene);

        //rect.addEventHandler(MouseEvent.MOUSE_CLICKED, new EventHandler<MouseEvent>()
        scene.addEventHandler(MouseEvent.MOUSE_CLICKED, new EventHandler<MouseEvent>() {
        @Override public void handle(MouseEvent event) {
              Circle circle = new Circle(event.getSceneX(), event.getSceneY(),30);
              circle.setFill(Color.YELLOW);
              root.getChildren().add(circle);
        }
     });
    //root.getChildren().add(circle);
    primaryStage.setScene(new Scene(root, 300, 250));
    primaryStage.show();
}
}

I am trying to put an circle on stage when mouse is pressed, I am unable to make it happen. I tried setting the root at the beginning, but it doesn't happen. Help appreciated !

回答1:

I made just a few edits to your code and it seems to work perfectly !

Note : You need not set the root again inside the scene as you have already did it in the beginning !

Same goes for setting the scene to the Stage !

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.input.MouseEvent;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

/**
 * A sample that demonstrates how to add or remove a change listener on a node
 * (for example, a Rectangle node) for some property (for example,
 * Rectangle.hover). Once you add a listener, the text field  shows the hover
 * property change.
 *
 * @see javafx.beans.value.ChangeListener
 * @see javafx.beans.InvalidationListener
 * @see javafx.beans.value.ObservableValue
 */
public class ChangeListenerSample extends Application {

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        final Group root = new Group();
        primaryStage.setResizable(false);
        Scene scene = new Scene(root, 400,80);
        primaryStage.setScene(scene);

        //rect.addEventHandler(MouseEvent.MOUSE_CLICKED, new EventHandler<MouseEvent>()
        scene.addEventHandler(MouseEvent.MOUSE_CLICKED, new EventHandler<MouseEvent>() {
        @Override public void handle(MouseEvent event) {
              Circle circle = new Circle(event.getSceneX(), event.getSceneY(),30);
              circle.setFill(Color.YELLOW);
              root.getChildren().add(circle);
        }
        });
        //root.getChildren().add(circle);
        primaryStage.show();

    }
}

来源：https://stackoverflow.com/questions/22677110/putting-an-object-on-a-stage-when-mouse-clicked