How to implement a constantly active loop to check for changes? - loops

Question

I created an empty TextField test and an empty TextField test2 in the "start" method
public void start(Stage primaryStage) throws Exception {}
Now I want to check constantly if test.getText().equals(""). If so, test2.setEditable(false), otherwise test2.setEditable(true).
I don't know how to implement it, as it needs to get checked constantly.
I already tried to implement an if-Statement in the start method and it actually set test2 on notEditable at the beginning, astest is empty but when test.getText().equals("") changed to !test.getText().equals("") test2 was still not editable.

Answer 1

You can do this by binding the editable property of test2 to the text property of test.
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
public class Main extends Application {
#Override
public void start(Stage primaryStage) {
TextField test = new TextField();
TextField test2 = new TextField();
// do the binding
test2.editableProperty().bind(test.textProperty().isEmpty().not());
VBox root = new VBox(20, test, test2);
root.setAlignment(Pos.CENTER);
root.setPadding(new Insets(50));
primaryStage.setScene(new Scene(root, 300, 150));
primaryStage.setTitle("Example");
primaryStage.show();
}
}
The text property of TextField is a StringProperty. This class has the method isEmpty (inherited by StringExpression) that returns a BooleanBinding that will hold true if the StringProperty's value is empty or null. The not() call negates the value of the BooleanBinding which means test2 will only be editable if test's text is not empty.

Answer 2

Instead of checking all the time you can just listen on changes like this:
test.textProperty().addListener((observable, oldValue, newValue) -> {
if (newValue.equals("")) {
test2.setEditable(false);
}
);