How to create new items and show in scene JavafX?

[Mohammad Rahman]

Hi. I want to add and remove new items on menu click. Now here is my menu

 

     Menu m = new Menu("Click For Options"); 
  
        // create menuitems 
        MenuItem m1 = new MenuItem("Coin Calculator"); 
        m.getItems().add(m1); 

Now I have a scene but in the same scene on clicking m1 I want to create textArea and add to scene and validate user input on click OK

   

 //create event for menu items
        m1.setOnAction(e-> {
        	
        	TextArea text1=new TextArea("Enter total coin to be exchanged");
        	TextArea text2=new TextArea("Enter coin type to exchange to");
        	VBox newBox=new VBox();
        	newBox.getChildren().removeAll();
        	newBox.getChildren().addAll(text1,text2);
			Group group = new Group(newBox);
			 newBox.getChildren().addAll(group);
        });

Its giving long lists of exceptions

    Exception in thread "JavaFX Application Thread" java.lang.IllegalArgumentException: Children: cycle detected: parent = VBox@313448d4, node = Group@2beac4d5
	at javafx.graphics/javafx.scene.Parent$3.onProposedChange(Parent.java:549)
	at javafx.base/com.sun.javafx.collections.VetoableListDecorator.addAll(VetoableListDecorator.java:234)
	at javafx.base/com.sun.javafx.collections.VetoableListDecorator.addAll(VetoableListDecorator.java:103)
	at assignment1/com.york.algorithm.CoinSorterGUI.lambda$0(CoinSorterGUI.java:101)
	at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
	at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
	at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
	at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
	at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
	at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
	at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
	at javafx.controls/javafx.scene.control.MenuItem.fire(MenuItem.java:465)

.....

[Zachary Griggs]

Hey, welcome to the Ranch!

The issue causing the exception is that your Group contains "newBox" because of this line:

Group group = new Group(newBox);

And you are also trying to add the group to newBox here:

newBox.getChildren().addAll(group);

In JavaFX, this sort of circular dependency is not allowed.

However even if you get this fixed, it doesn't look like the code in the m1 action really does anything. It creates a new VBox and Group, but doesn't end up doing anything with them, so you'll never see those items anywhere. I'd recommend not creating new elements, and rather have the elements exist immediately and hide them. Then in the m1 code, you can un-hide them.

[Mohammad Rahman]

Thanks!

Zachary Griggs wrote:Hey, welcome to the Ranch!

The issue causing the exception is that your Group contains "newBox" because of this line:

Group group = new Group(newBox);

And you are also trying to add the group to newBox here:

newBox.getChildren().addAll(group);

In JavaFX, this sort of circular dependency is not allowed.

However even if you get this fixed, it doesn't look like the code in the m1 action really does anything. It creates a new VBox and Group, but doesn't end up doing anything with them, so you'll never see those items anywhere. I'd recommend not creating new elements, and rather have the elements exist immediately and hide them. Then in the m1 code, you can un-hide them.