Getting text from TextArea in a GridPane in JavaFX

Question

I have a project in which I ask a user what type of electronic devices they use to tell them how many solar panels and batteries they need.

To collect information, I use a gridPane with three columns, in which there are TextArea, and a variable amount of rows. I need to collect the information in the second and third row of the gridPane.

I use the following method which I found on another question asked here.

private void calculer(ActionEvent event)
{
    double ampApp = 0;
    double heureApp = 0;
    double wattTotal = 0;
    double nbJourAuto;
    double heureSoleil;
    int nbPanneau;
    int nbBatterie;
    String stringTemp;

    for(int i =1; i < rangee; i++)
    {
        stringTemp = getNodeByRowColumnIndex( i, 1, gridApp).toString();
        ampApp += parseDouble(stringTemp);
    }

    for(int i =1; i < rangee; i++)
    {
        stringTemp = getNodeByRowColumnIndex(i, 2, gridApp).toString();
        heureApp += parseDouble(stringTemp);
    }

(it's only the first part of the method, I know there is a missing "}")

And here is the getNodeByRowColumnIndex code:

public Node getNodeByRowColumnIndex( final int row, final int column, GridPane gridPane) {
   Node result = null;
   ObservableList<Node> childrens = gridPane.getChildren();
   for(Node node : childrens) 
   {
        if(gridPane.getRowIndex(node) == row && gridPane.getColumnIndex(node) == column) 
        {
           result = node;
           break;
        }
   }
   return result;
}

I tried this method, but keep getting java.lang.NullPointerException

Does anyone knows why and how to solve this issues?

Edit :

As requested here's the stack trace

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8411)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:380)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:294)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:416)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:415)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 48 more
Caused by: java.lang.NullPointerException
at systemesolaire.FXMLDocumentController.getNodeByRowColumnIndex(FXMLDocumentController.java:111)
at systemesolaire.FXMLDocumentController.calculer(FXMLDocumentController.java:81)
... 58 more

and here's how I intialize my children (I used SceneBuilder so here is the FXML file)

<content>
        <GridPane fx:id="gridApp" prefHeight="141.0" prefWidth="452.0">
           <columnConstraints>
              <ColumnConstraints hgrow="SOMETIMES" maxWidth="226.0" minWidth="10.0" prefWidth="226.0" />
              <ColumnConstraints hgrow="SOMETIMES" maxWidth="146.0" minWidth="10.0" prefWidth="123.0" />
              <ColumnConstraints hgrow="SOMETIMES" maxWidth="113.0" minWidth="10.0" prefWidth="103.0" />
           </columnConstraints>
           <rowConstraints>
              <RowConstraints minHeight="40.0" prefHeight="40.0" vgrow="NEVER" />
              <RowConstraints minHeight="40.0" prefHeight="40.0" vgrow="NEVER" />
              <RowConstraints minHeight="40.0" prefHeight="40.0" vgrow="NEVER" />
           </rowConstraints>
           <children>
              <Label text="  Nom de l'appareil">
                 <font>
                    <Font name="Anke" size="18.0" />
                 </font>
              </Label>
              <Label text="Ampérage" GridPane.columnIndex="1">
                 <font>
                    <Font name="Anke" size="14.0" />
                 </font>
              </Label>
              <Label text="Heures utilisation" GridPane.columnIndex="2">
                 <font>
                    <Font name="Anke" size="13.0" />
                 </font>
              </Label>
              <TextArea prefHeight="200.0" prefWidth="200.0" promptText="Nom" GridPane.rowIndex="1" />
              <TextArea prefHeight="200.0" prefWidth="200.0" promptText="Amp" GridPane.columnIndex="1" GridPane.rowIndex="1" />
              <TextArea prefHeight="200.0" prefWidth="200.0" promptText="Heure" GridPane.columnIndex="2" GridPane.rowIndex="1" />
              <TextArea prefHeight="200.0" prefWidth="200.0" promptText="Nom" GridPane.rowIndex="2" />
              <TextArea prefHeight="200.0" prefWidth="200.0" promptText="Amp" GridPane.columnIndex="1" GridPane.rowIndex="2" />
              <TextArea prefHeight="200.0" prefWidth="200.0" promptText="Heure" GridPane.columnIndex="2" GridPane.rowIndex="2" />
           </children>
        </GridPane>
     </content>

And here is How I add a row to my gridPane

 @FXML
private void ajouteRangee(ActionEvent event) 
{

   TextArea nom =  new TextArea();
   TextArea amp = new TextArea();
   TextArea heure = new TextArea();



   nom.setPromptText("Nom");
   amp.setPromptText("Amp");
   heure.setPromptText("heure");


   gridApp.addRow(rangee, nom, amp, heure);
   gridApp.layout();
   rangee++;

}

Answer 1

I got the answer with the help of my teacher, if anybody has the same issue, here's how I solved it.

The NullPointerException came for the getColumnIndex, the solution bypasses the issue, but I don't know why I was getting this exception in the first place.

Since the amount of rows and columns is known, there is no need to search every node for the right one. Also, since the number of children per row is the same, there is a logical way to get a specific children. Here's how :

 public TextArea getNodeByRowColumnIndex( final int row, final int column, GridPane gridPane) 
{

   ObservableList<Node> childrens = gridPane.getChildren();
   TextArea result = (TextArea) childrens.get((row*3)+column);

   return result;
}

The ObservableList gets children from left to right row by row, so you can get to a specific object in the list with this formula (((rowIndex + 1) * the amount of object per row) + on which column is your object)

And then you can get the TextArea text by doing:

 stringTemp = getNodeByRowColumnIndex( i, 1, gridApp).getText();