Lazy loading of items in a TableView

Question

I am implementing a custom TableCellFactory for asynchronously loading data from a database. The db request should not block the user interface thread.

public abstract class AsynchronousTableCellFactory<E, T> implements Callback<TableColumn<E, T>, TableCell<E, T>> {

private static final Executor exe1 = Executors.newFixedThreadPool(2);

private static final Executor exe2 = Executors.newFixedThreadPool(2);

@Override
public TableCell<E, T> call(final TableColumn<E, T> param) {
    final TableCell<E, T> cell = new TableCell<E, T>() {

        @Override
        public void updateItem(final T item, final boolean empty) {

            super.updateItem(item, empty);

            if (empty) {
                setText(null);
            } else {
                setText("Thinking..");
                // do this later some time, we need to finish here FAST
                exe1.execute(() -> {

                    if (getTableRow() != null) {
                        final Service<T> service = new Service<T>() {

                            @Override
                            protected Task<T> createTask() {
                                return getTask((E) getTableRow().getItem());
                            }
                        };
                        service.setExecutor(exe2);
                        service.setOnSucceeded(e -> {

                            if (e.getSource().getValue() == null) {
                                setText("n/a");
                            } else {
                                setText(e.getSource().getValue().toString());
                            }

                        });
                        service.setOnFailed(e -> {
                            final Throwable t = e.getSource().getException();
                            setText(t.getLocalizedMessage());
                        });
                        service.start();
                    }
                });
            }
        }
    };

    return cell;
}

protected abstract Task<T> getTask(E rowDataItem);

}

It works most of the time, but not always. One strange thing is that T itemalways null. In what cases can I expect what T itemwill happen null?

Corresponding table code:

public class OriginsTableViewController implements Initializable {

@FXML
private TableView<LazyLoadingOriginWrapper> table;
@FXML
private TableColumn<LazyLoadingOriginWrapper, String> cSampleName;

@Override
public void initialize(final URL location, final ResourceBundle resources) {
    cSampleName.setCellFactory(new AsynchronousOriginTableCellFactory<>(e -> e.getSampleName()));

}

EDIT: Find a better approach here .

Answer 1

, a TableCell ! , ( updateItem). , TableCell .

- ObservableValue LazyLoadingOriginWrapper CellValueFactory TableCell. ObservableValue TableView (, ObservableValue "fx-application"!). .

public static class LazyLoadingOriginWrapper
{
    // params are 'bean', 'id/name', 'default value'
    ObservableStringValue name = new SimpleStringProperty(this, "name", "thinking...");

    public ObservableStringValue nameProperty() { return name; }

    public void setName(String value)
    {
         Platform.runLater(() -> name.set(value));
     }

    // add your logic for asynchronious loading here and update the above ObservableValue instead. Make sure you trigger it manually!
}

@Override
public void initialize(final URL location, final ResourceBundle resources) {
    cSampleName.setCellValueFactory(C -> C.getValue().nameProperty());
}