How to clear a JavaFx TextField with TextFormatter - javafx

Question

I got a Double TextField example from some web site. It does work fine, but I have two problems:
The TextFormatter constructor requires a default value if one wants to have both a converter and a filter. I would like that default value NOT to be displayed when I launch the application but could not find how to do it.
I added to the example a button to clear the two TextFields, this triggers a NullPointerException when executing textField.clear(); how to I clear such a TextField?
Here is the code:
package sample;
import java.util.function.UnaryOperator;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TextField;
import javafx.scene.control.TextFormatter;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.util.StringConverter;
public class DoubleFieldExample extends Application {
#Override
public void start(Stage primaryStage) {
final TextField field = new TextField();
final TextField field2 = new TextField();
final Button clearBtn = new Button("Clear Text Fields");
final Double defaultValue = 0.5;
final UnaryOperator<TextFormatter.Change> numberOnlyFilter = change -> {
final String text = change.getText();
return (text.isEmpty() || text .matches("[0-9.eE+-]")) ? change : null;
};
final StringConverter<Double> NumberConverter = new StringConverter<Double>() {
#Override
public String toString(Double value) {
return (value == null) ? null : value.toString();
}
#Override
public Double fromString(String text) {
return (text == null || text.trim().isEmpty()) ? null : Double.parseDouble(text.trim());
}
};
final TextFormatter<Double> numberOnlyFormatterField1 = new TextFormatter<Double>(NumberConverter, defaultValue, numberOnlyFilter);
final TextFormatter<Double> numberOnlyFormatterField2 = new TextFormatter<Double>(NumberConverter, defaultValue, numberOnlyFilter);
field.setTextFormatter(numberOnlyFormatterField1);
field2.setTextFormatter(numberOnlyFormatterField2);
numberOnlyFormatterField1.valueProperty().addListener((observable, oldValue, newValue) -> System.out.printf("%s -> %s%n", oldValue, newValue));
clearBtn.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
field.clear();
field2.clear();
}
});
final StackPane root = new StackPane();
root.getChildren().addAll(new VBox(field, field2, clearBtn));
final Scene scene = new Scene(root, 300, 250);
primaryStage.setTitle("Test");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}

Answer 1

Setting the text to null via the text formatter's converter causes a null pointer exception in JavaFX version 8, but not in later versions (it works fine in version 11 and later: I am not sure in which exact version the issue was fixed).
In any case, you can avoid doing this by representing a null value as an empty string, instead of a null string:
final StringConverter<Double> NumberConverter = new StringConverter<Double>() {
#Override
public String toString(Double value) {
// return (value == null) ? null : value.toString();
return (value == null) ? "" : value.toString();
}
#Override
public Double fromString(String text) {
return (text == null || text.trim().isEmpty()) ? null : Double.parseDouble(text.trim());
}
};
With this fix, you can now make the default value null instead of some arbitrary value, which will initialize the text fields as empty:
final Double defaultValue = null;