JavaFX Editing Gridpane from FXML File

Question

I wanted to add Labels to my gridpane via java; therefore, I used the following code:

public class Controller {   
@FXML

private Button addTeam;
private GridPane teams;

public void addTeam(ActionEvent e) throws Exception {
        if(e.getSource()==addTeam) {
            Label apple = new Label("hello");
            teams.setConstraints(apple, 0, 0);
            teams.getChildren().add(apple);
        }
}

When I ran the code, I get a NullPointerException wrapped in an InvocationTargetException.

What exactly is null here? From my current understanding, the '@FXML' tag instantiates the variables that I declared below it.

Stack:

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java
.lang.reflect.InvocationTargetException
        at javafx.fxml.FXMLLoader$MethodHandler.invoke(Unknown Source)
        at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(Unknown So
urce)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unkn
own Source)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknow
n Source)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknow
n Source)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(U
nknown Source)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
        at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
        at javafx.event.Event.fireEvent(Unknown Source)
        at javafx.scene.Node.fireEvent(Unknown Source)
        at javafx.scene.control.Button.fire(Unknown Source)
        at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(Un
known Source)
        at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown S
ource)
        at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown S
ource)
        at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.h
andleBubblingEvent(Unknown Source)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unkn
own Source)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknow
n Source)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknow
n Source)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(U
nknown Source)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Sourc
e)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Sou
rce)
        at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
        at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
        at javafx.event.Event.fireEvent(Unknown Source)
        at javafx.scene.Scene$MouseHandler.process(Unknown Source)
        at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source)
        at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
        at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotificatio
n.run(Unknown Source)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotificatio
n.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEve
nt$355(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown
 Source)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unkn
own Source)
        at com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
        at com.sun.glass.ui.View.notifyMouse(Unknown Source)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.lambda$null$149(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at sun.reflect.misc.Trampoline.invoke(Unknown Source)
        at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
        ... 61 more
Caused by: java.lang.NullPointerException
        at GuiController.addTeam(GuiController.java:42)
        ... 70 more

The `@FXML` tag initializes the variables to the instances created by the `FXMLLoader` when it reads the FXML file. So you'd really need to show your FXML file to know for sure. And it would *really* help if you could indicate which line in the code you posted is line 42. Having said all that... since you don't have a `@FXML` annotation on the `teams` variable, only on the `addTeam` variable, it seem highly likely that `teams` is `null` (and that line 42 is the first line referring to `teams`: `teams.setConstraints(...)`). — James_D, Dec 10 '15 at 02:51
Sadly, I thought that FXML tag would only need to be used once, but as you said, I have to annotate each variable with the FXML tag. Thanks for your help! — Rhendz, Dec 10 '15 at 23:28
The annotation is simply part of the statement. Note there is no semicolon between `@FXML` and the subsequent code, so the entire statement is `@FXML private Button addTeam;`. The next code forms the next statement: `private GridPane teams;` (Technically annotations are modifiers: `@FXML` has the same status in the declaration as the keyword `private`.) — James_D, Dec 11 '15 at 00:59

score 0 · Answer 1 · answered Dec 11 '15 at 00:40

0

Make sure that each variable you are referencing from the FXML file has the @FXML annotation in your code. The @FXML tag removes the need for instantiating your variables, and in essence, it looks up the variable using the fx:id.

answered Dec 11 '15 at 00:40

Rhendz

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JavaFX Editing Gridpane from FXML File

1 Answers1