JavaFX start method everytime included tabcontent is called - tabs

Question

How can I start a method every time a tab is called? I have a Main.fxml with a tabpane and two tabs, I've included a separate fxml for each tab (tab1.fxml, tab2.fxml).
Main.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane prefHeight="434.0" prefWidth="428.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.MainController">
<children>
<TabPane prefHeight="434.0" prefWidth="428.0" tabClosingPolicy="UNAVAILABLE" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<tabs>
<Tab fx:id="tab1" text="Tab 1">
<content>
<fx:include source="tab1.fxml" />
</content>
</Tab>
<Tab fx:id="tab2" onSelectionChanged="#addView" text="Tab 2">
<content>
<fx:include source="tab2.fxml" />
</content>
</Tab>
</tabs>
</TabPane>
</children>
</AnchorPane>
MainController.java
public class MainController implements Initializable{
#FXML private Tab tab1;
#FXML private Tab tab2;
#Override
public void initialize(URL arg0, ResourceBundle arg1) {
}
#FXML public void addView(){
}
}
Each FXML has a Label which should show how often the tab(content) was called. So if I click on tab ("tab2") the counter label should show "1" and increment by +1 every time I call this tab again. This should happen by using a method within the tab controllers.
tab1.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane prefHeight="249.0" prefWidth="257.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.tab1Controller">
<children>
<Label fx:id="lbl_1" layoutX="92.0" layoutY="53.0" text="not clicked" />
</children>
</AnchorPane>
tab1Controller.java
public class tab1Controller implements Initializable{
#FXML public Label lbl_1;
private static int counter=0;
#Override
public void initialize(URL arg0, ResourceBundle arg1) {
}
public void addViewCounter(){
lbl_1.setText(""+counter);
counter++;
}
}
Tab2.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane prefHeight="249.0" prefWidth="257.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.tab2Controller">
<children>
<Label fx:id="lbl_2" layoutX="92.0" layoutY="53.0" text="not clicked" />
</children>
</AnchorPane>
tab2Controller.java
public class tab1Controller implements Initializable{
#FXML public Label lbl_2;
private static int counter=0;
#Override
public void initialize(URL arg0, ResourceBundle arg1) {
}
public void addViewCounter(){
lbl_2.setText(""+counter);
counter++;
}
}
I've already tried to solve this problem by using static methods and labels but i get NullPointerExceptions, seems like this doesn't work anymore with java 8.
Also I've tried to get the controller by using a FXMLloader ... this way I also get a NullPointerExceptions.
Isn't there an onCall method for the included fmxl or the anchorpane? Or maybe something that makes the controller initialize again.
Any other solutions or ideas?

Answer 1

Firstly, your counters should not be static. They belong to the controller instances, not the controller class.
You need three things:
A reference to the tabPane in the main controller
A reference to each of the tab controllers in the main controller.
A listener on the tabPane's selected tab, so that you can call a method when the selected tab changes
For the first, just do:
<TabPane fx:id="tabPane" prefHeight="434.0" ... >
in Main.fxml, and
#FXML private TabPane tabPane ;
in MainController.java.
For the second, you can use the "Nested Controller" technique.
You need to add an fx:id attribute to each of the fx:includes, and then just add references for the controllers in MainController.java. The rule is that if your fx:include has fx:id="x", then the controller from the corresponding FXML file can be injected into a variable with name xController. Here I have changed the class names for the controllers to Tab1Controller and Tab2Controller to follow the standard conventions (and avoid confusion).
In Main.fxml, change the fx:includes to include an fx:id:
<fx:include fx:id="tab1Content" source="tab1.fxml" />
<fx:include fx:id="tab2Content" source="tab2.fxml" />
In MainController.java:
#FXML private Tab1Controller tab1ContentController ;
#FXML private Tab2Controller tab2ContentController ;
Now in MainController's initialize() method just set up the listener:
public void initialize() {
tabPane.getSelectionModel().selectedItemProperty()
.addListener((obs, oldTab, newTab) -> {
if (newTab == tab1) {
tab1ContentController.addViewCounter();
} else if (newTab == tab2) {
tab2ContentController.addViewCounter();
}
});
}