JavaFx: binding of a ObjectProperty<Integer> with a ObjectProperty<Unit> - binding

Question

I have a scene with a NumberSpinner element and a ComboBox element and I want to bind the minValue property of the NumberSpinner element with the valueProperty of the ComboBox element. Some code:
#FXML
private NumberSpinner aNumberSpinner;
#FXML
private ComboBox<Unit> aComboBox;
where Unit is an enum:
public enum Unit {
mm,
degree
}
What I want is that when I choose degree Unit in aComboBox the minValueProperty() of aNumberSpinner become 10. How can I achieve it?

Answer 1

As suggested by Kleopatra in comments it is best if the unit knows its own minimum.
Preferred solution - no binding
My preferred solution for this wouldn't use a binding at all.
A listener on the combobox value can easily set the minimum value of your spinner object directly to the appropriate value by querying the minimum value from the unit newly selected in the combo box.
Sometimes it is possible to be a bit too tricky with bindings...
import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.stage.Stage;
public class UnitMinimums extends Application {
private enum Unit {
mm(0), degree(10);
private final int minValue;
private Unit(int minValue) {
this.minValue = minValue;
}
public int getMinValue() {
return minValue;
}
}
private Slider slider = new Slider(0, 20, 0);
private ComboBox<Unit> combo = new ComboBox<>(
FXCollections.observableArrayList(
Unit.values()
)
);
#Override
public void start(Stage stage) throws Exception {
combo.valueProperty().addListener((observable, oldValue, newValue) ->
slider.setMin(newValue.getMinValue())
);
slider.setShowTickMarks(true);
slider.setShowTickLabels(true);
VBox layout = new VBox(5, slider, combo);
layout.setPadding(new Insets(10));
VBox.setVgrow(combo, Priority.ALWAYS);
combo.setMaxWidth(Double.MAX_VALUE);
combo.getSelectionModel().select(0);
stage.setScene(new Scene(layout));
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}
Pure Binding Solution
If you did want a pure binding solution, you could do something like below, but it has the disadvantage of scattering the information specific to the minimum value of the unit (which is intrinsic to the enum) all around the code if you started writing code like this a lot.
Use Bindings.when:
Bindings.when(
combo.valueProperty().isEqualTo(Unit.degree)
).then(10)
.otherwise(0)
Executable Sample
import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.collections.FXCollections;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.stage.Stage;
public class BoundMinimums extends Application {
private enum Unit { mm, degree }
private Slider slider = new Slider(0, 20, 0);
private ComboBox<Unit> combo = new ComboBox<>(
FXCollections.observableArrayList(
Unit.values()
)
);
#Override
public void start(Stage stage) throws Exception {
slider.minProperty().bind(
Bindings.when(
combo.valueProperty().isEqualTo(Unit.degree)
).then(10)
.otherwise(0)
);
slider.setShowTickMarks(true);
slider.setShowTickLabels(true);
VBox layout = new VBox(5, slider, combo);
layout.setPadding(new Insets(10));
VBox.setVgrow(combo, Priority.ALWAYS);
combo.setMaxWidth(Double.MAX_VALUE);
stage.setScene(new Scene(layout));
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}
On datatype conversion
This gets a little complicated and non-obvious for me (which is another reason to sometimes prefer listeners and straight setters over binding), but I think you can do something like below, which coverts the DoubleProperty slider.minProperty() to an ObjectProperty<Integer>:
ObjectProperty<Integer> op = new SimpleObjectProperty<>(5);
op.bind(
IntegerExpression.integerExpression(
slider.minProperty()
).asObject()
);
Putting it together with the unit conversion, you get the following, which maybe even does what you want:
ObjectProperty<Integer> op = new SimpleObjectProperty<>(5);
op.bind(
IntegerExpression.integerExpression(
Bindings.when(
combo.valueProperty().isEqualTo(Unit.degree)
).then(10)
.otherwise(0)
).asObject()
);