One ChangeListener for multiple TextFields in Javafx

Question

I want to use a single ChangeListener for multiple TextFields in my application.

I know that you can create a listener object and add this to all TextFields, then you can check via the event key which TextField-Object triggered the event.

With lamda expression I could use this for every TextField, unfortunately this isn't suited for my problem. I use the input of all TextFields so one single Listener should be enough.

TextField textField = new TextField();
textField.textProperty().addListener((observable, oldValue, newValue) -> {
    System.out.println("textfield changed from " + oldValue + " to " + newValue);
});

Answer 1

As Slaw pointed out in his comment, you can easily create a single ChangeListener and then apply it to each of your TextField nodes.

ChangeListener<String> listener = ((observable, oldValue, newValue) -> {
    System.out.println("TextField changed from " + oldValue + " to " + newValue + "!");
});

Here is a complete sample you can run to see it in action:

import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.ListView;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

import java.util.ArrayList;
import java.util.Arrays;

public class ReusableListenerSample extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {

        // Simple Interface
        VBox root = new VBox(10);
        root.setAlignment(Pos.CENTER);
        root.setPadding(new Insets(10));

        // Create a ChangeListener that we will apply to multiple TextFields
        ChangeListener<String> listener = ((observable, oldValue, newValue) -> {
            System.out.println("TextField changed from " + oldValue + " to " + newValue + "!");
        });

        // Create some TextFields
        TextField txt1 = new TextField();
        TextField txt2 = new TextField();
        TextField txt3 = new TextField();

        // Now, we can add our preconfigured listener to each of the TextFields
        txt1.textProperty().addListener(listener);
        txt2.textProperty().addListener(listener);
        txt3.textProperty().addListener(listener);

        // Add our TextFields to the scene
        root.getChildren().addAll(txt1, txt2, txt3);

        // Show the stage
        primaryStage.setScene(new Scene(root));
        primaryStage.setTitle("ListViewSample Sample");
        primaryStage.show();

    }
}

---

Now, the above example does not indicate which TextField was changed. In order to track that, you could create your own inner class that implements ChangeListener<String> and pass your TextField (or any other data to it):

class MyChangeListener implements ChangeListener<String> {

    private final TextField myTextField;

    public MyChangeListener(TextField myTextField) {
        this.myTextField = myTextField;
    }

    @Override
    public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
        System.out.println(myTextField + " changed from " + oldValue + " to " + newValue + "!");
    }
}

Then, just add a new instance of that MyChangeListener to each TextField instead:

txt1.textProperty().addListener(new MyChangeListener(txt1));