如果解析失败，取消表格单元格编辑的规范方法

Question

Edit :
I first voted to close as a duplicate after finding this answer by James_D, which sets a TextFormatter on a TextField . But then firstly I found that (in a TableView context) the method TextFieldTableCell.forTableColumn() does not in fact draw a TextField when it starts editing, but instead a LabeledText , which does not subclass TextInputControl , and therefore does not have setTextFormatter() .
Secondly, I wanted something which acted in a familiar sort of way. I may have produced the "canonical" solution in my answer: let others judge.

---

This is a TableColumn in a TableView (all Groovy):

TableColumn<Person, String> ageCol = new TableColumn("Age")
ageCol.cellValueFactory = { cdf -> cdf.value.ageProperty() }

int oldAgeValue
ageCol.onEditStart = new EventHandler(){
    @Override
    public void handle( Event event) {
        oldAgeValue = event.oldValue
    }
}
ageCol.cellFactory = TextFieldTableCell.forTableColumn(new IntegerStringConverter() {
    @Override
    public Integer fromString(String value) {
        try {
            return super.fromString(value)
        }
        catch ( NumberFormatException e) {
            // inform user by some means...
            println "string could not be parsed as integer..."
            // ... and cancel the edit
            return oldAgeValue
        }
    }
})

Excerpt from class Person:

public class Person {
    private IntegerProperty age;
    public void setAge(Integer value) { ageProperty().set(value) }
    public Integer getAge() { return ageProperty().get() }
    public IntegerProperty ageProperty() {
        if (age == null) age = new SimpleIntegerProperty(this, "age")
        return age
    }
    ...

Without the start-edit Handler , when I enter a String which can't be parsed as an Integer NumberFormatException not surprisingly gets thrown. But I also find that the number in the cell then gets set to 0, which is likely not to be the desired outcome.

But the above strikes me as a pretty clunky solution.

I had a look at ageCol , and ageCol.cellFactory (as these are accessible from inside the catch block) but couldn't see anything better and obvious. I can also see that one can easily obtain the Callback ( ageCol.cellFactory ), but calling it would require the parameter cdf , ie the CellDataFeatures instance, which again you'd have to store somewhere.

I'm sure a validator mechanism of some kind was involved with Swing: ie before a value could be transferred from the editor component (via some delegate or something), it was possible to override some validating mechanism. But this IntegerStringConverter seems to function as a validator, although doesn't seem to provide any way to revert to the existing ("old") value if validation fails.

Is there a less clunky mechanism than the one I've shown above?

Answer 1

Edit
NB improved after kleopatra's valuable insights.
Edit2
Overhauled completely after realising that the best thing is to use the existing default editor and tweak it.

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I thought I'd give an example with a LocalDate , slightly more fun than Integer . Given the following class:

class Person(){ 
...
private ObjectProperty<LocalDate> dueDate;
public void setDueDate(LocalDate value) {
    dueDateProperty().set(value);
}
public LocalDate getDueDate() {
    return (LocalDate) dueDateProperty().get();
}
public ObjectProperty dueDateProperty() {
    if (dueDate == null) dueDate = new SimpleObjectProperty(this, "dueDate");
    return dueDate;
}

Then you create a new editor cell class, which is exactly the same as TextFieldTreeTableCell (subclass of TreeTableCell ), which is used by default to create an editor for a TreeTableView 's table cell. However, you can't really subclass TextFieldTreeTableCell as, for example, its essential field textField is private .

So you copy the code in full from the source* (only about 30 lines), and you call it

class DueDateEditor extends TreeTableCell<Person, LocalDate> { 
    ...

You then have to create a new StringConverter class, subclassing LocalDateStringConverter . The reason for subclassing is that if you don't do that it is impossible to catch the DateTimeParseException thrown by fromString() when an invalid date is received: if you use LocalDateStringConverter the JavaFX framework unfortunately catches it, without any frames in the stack trace involving your own code. So you do this:

class ValidatingLocalDateStringConverter extends LocalDateStringConverter {
    boolean valid;
    LocalDate fromString(String value) {
        valid = true;
        if (value.isBlank()) return null;
        try {
            return LocalDate.parse(value);
        } catch (Exception e) {
            valid = false;
        }
        return null;
    }
}

Back in your DueDateEditor class you then rewrite the startEdit method as follows. NB, as with the TextFieldTreeTableCell class, textField is actually created lazily, when you first edit.

@Override
void startEdit() {
    if (! isEditable()
            || ! getTreeTableView().isEditable()
            || ! getTableColumn().isEditable()) {
        return;
    }
    super.startEdit();

    if (isEditing()) {
        if (textField == null) {
            textField = CellUtils.createTextField(this, getConverter());

            // this code added by me
            ValidatingLocalDateStringConverter converter = getConverter();
            Callable bindingFunc = new Callable(){
                @Override
                Object call() throws Exception {
                    // NB the return value from this is "captured" by the editor
                    converter.fromString( textField.getText() );
                    return converter.valid? '' : "-fx-background-color: red;";
                }
            }
            def stringBinding = Bindings.createStringBinding( bindingFunc, textField.textProperty() );
            textField.styleProperty().bind( stringBinding );


        }
        CellUtils.startEdit(this, getConverter(), null, null, textField);
    }
}

NB don't bother trying to look up CellUtils : this is package-private, the package in question being javafx.scene.control.cell.

To set things up you do this:

Callback<TreeTableColumn, TreeTableCell> dueDateCellFactory =
        new Callback<TreeTableColumn, TreeTableCell>() {
            public TreeTableCell call(TreeTableColumn p) {
                return new DueDateEditor( new ValidatingLocalDateStringConverter() );
            }
        }
dueDateColumn.setCellFactory(dueDateCellFactory);

... the result is a nice, reactive editor cell: when containing an invalid date (acceptable pattern yyyy-mm-dd ; see other LocalDate.parse() variant for other formats) the background is red, otherwise normal. Entering with a valid date works seamlessly. You can also enter an empty String , which is returned as a null LocalDate .

With the above, pressing Enter with an invalid date sets the date to null . But overriding things to prevent this happening (ie forcing you to enter a valid date, or cancel the edit, eg by Escape) is trivial, using the ValidatingLocalDateStringConverter 's valid field:

@Override
void commitEdit( LocalDate newDueDate ){
    if( getConverter().valid )
        super.commitEdit( newDueDate );
}

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* I couldn't find this online. I extracted from the javafx source .jar file javafx-controls-11.0.2-sources.jar