I'm currently writing a little Gui application with javaFx. I have a class App wich extends Application and wich is the controller of HauptFenster.fxml. This class builds up a Window with a menubar and a tabPane. Then I add the SplitPane from Uebersicht.fxml. The controller of Uebersicht.fxml is Uebersicht.java. Up to here everything working. But if I click a button which calls a Method, all of my fields in App are null. So all my fields get deleted by the JavaFX thread after the method "start" is called. You can see this with a debugger. Why is this happening? P.S: I removed all unnecessary code, so it shows only the Error, the Program does not make any practical Sense like it´s shown here.
App.Java:
import java.io.IOException;
import javafx.application.Application;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.control.SplitPane;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
import view2.Uebersicht;
public class App extends Application {
private Stage primaryStage;
private BorderPane rootLayout;
private SplitPane uebersichtPane;
private Uebersicht uebersicht;
private ObservableList<Tab> tabs;
public App() {
}
@Override
public void start(Stage primaryStage) throws Exception {
this.primaryStage = primaryStage;
this.primaryStage.setTitle("FunktionsApp");
initHauptfenster();
initÜbersicht();
}
private void initHauptfenster() {
try {
// Load root layout from fxml file.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(App.class.getResource("Hauptfenster.fxml"));
rootLayout = (BorderPane) loader.load();
tabs= ((TabPane) rootLayout.getCenter()).getTabs();
// Show the scene containing the root layout.
Scene scene = new Scene(rootLayout);
primaryStage.setScene(scene);
primaryStage.show();
} catch (IOException e) {
e.printStackTrace();
}
}
private void initÜbersicht() {
try {
// Load root layout from fxml file.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(App.class.getResource("Uebersicht.fxml"));
uebersichtPane= (SplitPane) loader.load();
tabs.get(0).setContent(uebersichtPane);
uebersicht = loader.getController();
uebersicht.initText();
} catch (IOException e) {
e.printStackTrace();
}
}
@FXML
private void deleteFunktion() {
uebersicht.initText();
}
@FXML
public void speichern() {
uebersicht.initText();
}
@FXML
public void laden() {
uebersicht.initText();
}
public static void main(String[] args) {
launch(args);
}
}
Uebersicht.java
import javafx.fxml.FXML;
import javafx.scene.canvas.Canvas;
import javafx.scene.control.Label;
import view2.App;
public class Uebersicht {
@FXML
private Label lblStamm;
@FXML
private Label lblF;
@FXML
private Label lblF1;
@FXML
private Label lblF2;
@FXML
private Canvas canvas;
public void initText() {
lblStamm.setText("F(x)=");
lblF.setText("f(x)=");
lblF1.setText("f'(x)=");
lblF2.setText("f''(x)=");
}
}
HauptFenster.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import java.lang.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.BorderPane?>
<BorderPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="630.0" prefWidth="820.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="view2.App">
<center>
<TabPane prefHeight="200.0" prefWidth="200.0" tabClosingPolicy="UNAVAILABLE" BorderPane.alignment="CENTER">
<tabs>
<Tab text="Übersicht" />
<Tab text="Kurvendiskussion" />
<Tab text="Eingabe" />
</tabs>
</TabPane>
</center>
<top>
<MenuBar BorderPane.alignment="CENTER">
<menus>
<Menu mnemonicParsing="false" text="Datei">
<items>
<MenuItem mnemonicParsing="false" onAction="#speichern" text="Speichern" />
<MenuItem mnemonicParsing="false" onAction="#laden" text="Laden" />
</items>
</Menu>
<Menu mnemonicParsing="false" text="Edit">
<items>
<MenuItem mnemonicParsing="false" onAction="#deleteFunktion" text="Funktion löschen" />
</items>
</Menu>
<Menu mnemonicParsing="false" text="Help">
<items>
<MenuItem mnemonicParsing="false" text="About" />
</items>
</Menu>
</menus>
</MenuBar>
</top>
</BorderPane>
Uebersicht.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.*?>
<?import javafx.scene.text.*?>
<?import javafx.scene.canvas.*?>
<?import java.lang.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.BorderPane?>
<SplitPane dividerPositions="0.7264367816091954" orientation="VERTICAL" prefHeight="437.0" prefWidth="552.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="view2.Uebersicht">
<items>
<BorderPane>
<center>
<Canvas fx:id="canvas" BorderPane.alignment="CENTER" />
</center>
</BorderPane>
<ScrollPane vbarPolicy="NEVER">
<content>
<BorderPane>
<center>
<GridPane BorderPane.alignment="CENTER">
<columnConstraints>
<ColumnConstraints hgrow="SOMETIMES" percentWidth="100.0" />
</columnConstraints>
<rowConstraints>
<RowConstraints vgrow="NEVER" />
<RowConstraints minHeight="0.0" prefHeight="6.0" vgrow="NEVER" />
<RowConstraints vgrow="NEVER" />
<RowConstraints minHeight="0.0" prefHeight="6.0" vgrow="NEVER" />
<RowConstraints vgrow="NEVER" />
<RowConstraints minHeight="0.0" prefHeight="6.0" vgrow="NEVER" />
<RowConstraints vgrow="NEVER" />
</rowConstraints>
<children>
<Label fx:id="lblStamm" text="Label" wrapText="true">
<font>
<Font name="Times New Roman" size="25.0" />
</font>
<GridPane.margin>
<Insets bottom="2.0" />
</GridPane.margin>
</Label>
<Label fx:id="lblF" text="Label" wrapText="true" GridPane.rowIndex="2">
<font>
<Font name="Times New Roman" size="25.0" />
</font>
<GridPane.margin>
<Insets bottom="2.0" />
</GridPane.margin>
</Label>
<Label fx:id="lblF1" text="Label" wrapText="true" GridPane.rowIndex="4">
<font>
<Font name="Times New Roman" size="25.0" />
</font>
<GridPane.margin>
<Insets bottom="2.0" />
</GridPane.margin>
</Label>
<Label fx:id="lblF2" text="Label" wrapText="true" GridPane.rowIndex="6">
<font>
<Font name="Times New Roman" size="25.0" />
</font>
<GridPane.margin>
<Insets bottom="2.0" />
</GridPane.margin>
</Label>
<Separator prefWidth="200.0" GridPane.rowIndex="1" />
<Separator prefWidth="200.0" GridPane.rowIndex="3" />
<Separator prefWidth="200.0" GridPane.rowIndex="5" />
</children>
<padding>
<Insets bottom="5.0" left="5.0" right="5.0" top="5.0" />
</padding>
</GridPane>
</center>
</BorderPane>
</content>
</ScrollPane>
</items>
</SplitPane>
