Formatted TextField - javafx

Question

I'm trying to create a TextField whose content is validated with a template. To do this, I create a TextFormatter to which I pass a StringConverter.
However, I do notice a weird thing about using StringConverter<String>. When I enter invalid data and the field loses focus, it does not clear its content (it only clears it after subsequent focusing). For comparison, when I use StringConverter<LocalTime> this problem is not noticed.
If I catch the change of focus and validate the data, the problem is solved, but I wonder why there is a discrepancy in the validation in both cases.
public class Sample extends Application {
public static void main(String[] args) {
launch(args);
}
#Override
public void start(Stage primaryStage) {
TextField fieldA = new TextField();
fieldA.setPromptText("00000");
fieldA.setTextFormatter(new TextFormatter<>(new StringConverter<String>() {
#Override
public String toString(String object) {
if(object == null) return "";
return object.matches("[0-9]{5}") ? object : "";
}
#Override
public String fromString(String string) {
if(string == null) return null;
return string.matches("[0-9]{5}") ? string : null;
}
}));
// fieldA.focusedProperty().addListener((observable, oldValue, newValue) -> {
// if(!fieldA.textProperty().getValueSafe().matches("[0-9]{5}")) {
// fieldA.setText(null);
// }
// });
TextField fieldB = new TextField();
fieldB.setPromptText("HH:MM:SS");
fieldB.setTextFormatter(new TextFormatter<>(new StringConverter<LocalTime>() {
#Override
public String toString(LocalTime object) {
if(object == null) return "";
return object.format(DateTimeFormatter.ofPattern("HH:mm:ss"));
}
#Override
public LocalTime fromString(String string) {
if(string == null) return null;
return LocalTime.parse(string, DateTimeFormatter.ofPattern("HH:mm:ss"));
}
}));
VBox vBox = new VBox(fieldA, fieldB);
vBox.setSpacing(5);
primaryStage.setScene(new Scene(vBox));
primaryStage.show();
}
}
ps: note that the purpose is not to create a TextField that can only accept 5 numbers. This is just an example.

Answer 1

I found the reason for the discrepancy in behavior. The main problem is that updating controls is done by binding valueProperty (in TextFormatter) with textProperty (in TextField). Because notifications of change to all Property objects are only saturated when the value of the wrapper is changed, sequential null submission causes a one-time notification.
The different behavior when using StringConverter<LocalTime> is because LocalTime::parse() throws a DateTimeParseException exception in invalid formatting. This in turn leads to a new valueProperty value being set, and to a previous valid control value.
This is the specific snippet of TextFormatter that is responsible for this behavior.
void updateValue(String text) {
if (!value.isBound()) {
try {
V v = valueConverter.fromString(text);
setValue(v);
} catch (Exception e) {
updateText(); // Set the text with the latest value
}
}
}
And the solution to the problem is that implementing StringConverter::fromString with an invalid value, instead of returning null, should throw unchecked exceptions.
public class Sample extends Application {
public static void main(String[] args) {
launch(args);
}
#Override
public void start(Stage primaryStage) {
TextField fieldA = new TextField();
fieldA.setPromptText("00000");
fieldA.setTextFormatter(new TextFormatter<>(new StringConverter<String>() {
#Override
public String toString(String object) {
if(object == null) return "";
return object.matches("[0-9]{5}") ? object : "";
}
#Override
public String fromString(String string) {
if(string == null)
throw new RuntimeException("Value is null");
if(string.matches("[0-9]{5}")) {
return string;
}
throw new RuntimeException("Value not match");
}
}));
TextField fieldB = new TextField();
fieldB.setPromptText("HH:MM:SS");
fieldB.setTextFormatter(new TextFormatter<>(new StringConverter<LocalTime>() {
#Override
public String toString(LocalTime object) {
if(object == null) return "";
return object.format(DateTimeFormatter.ofPattern("HH:mm:ss"));
}
#Override
public LocalTime fromString(String string) {
if(string == null) return null;
return LocalTime.parse(string, DateTimeFormatter.ofPattern("HH:mm:ss"));
}
}));
VBox vBox = new VBox(fieldA, fieldB);
vBox.setSpacing(5);
primaryStage.setScene(new Scene(vBox));
primaryStage.show();
}
}