Map integer to string of custom class in combobox - javafx

Question

I have a tabelview that displays a list of appointees. Each appointe has a group assigned to it, the id of that group is saved in the appointe class.
I want to display a combobox inside a tablecell that displays the selected group and all other groups that exist. I can set the items of the combobox in the cell factory but i cant set the selected value of the respective appointee.
I have a method that returns the Group from the observable list when i provide it with the id. Thats means i need the id in the cellfactory but i didnt find a way to do this. I also need to display the name of the group and not the refernce to the clas. Is there a way to do this, or should i change my approach?
The Appointee class
public class Appointee {
private SimpleIntegerProperty id;
private SimpleStringProperty firstname;
private SimpleStringProperty lastname;
private SimpleIntegerProperty group;
private SimpleIntegerProperty assigned;
public Appointee(int id, String firstname, String lastname, int group, int assigned){
this.id = new SimpleIntegerProperty(id);
this.firstname = new SimpleStringProperty(firstname);
this.lastname = new SimpleStringProperty(lastname);
this.group = new SimpleIntegerProperty(group);
this.assigned = new SimpleIntegerProperty(assigned);
}
The Group class
public class Group {
private IntegerProperty id;
private StringProperty name;
private IntegerProperty members;
private IntegerProperty assigned;
public Group(int id, String name, int members, int assigned) {
this.id = new SimpleIntegerProperty(id);
this.name = new SimpleStringProperty(name);
this.members = new SimpleIntegerProperty(members);
this.assigned = new SimpleIntegerProperty(assigned);
}
The appointe table view
public AppointeeTableView() {
// define table view
this.setPrefHeight(800);
this.setColumnResizePolicy(TableView.CONSTRAINED_RESIZE_POLICY);
this.setItems(MainController.appointeeObervableList);
this.setEditable(true);
// define columns
...
TableColumn groupCol = new TableColumn("Group"); // group
groupCol.setCellFactory(col -> {
TableCell<Group, StringProperty> c = new TableCell<>();
final ComboBox<String> comboBox = new ComboBox(MainController.groupObservableList);
c.graphicProperty().bind(Bindings.when(c.emptyProperty()).then((Node) null).otherwise(comboBox));
return c;
});
groupCol.setEditable(false);
...
}

Answer 1

Override the updateItem method of the TableCell to update the cell, make sure the new value is saved on a change of the TableCell value and use a cellValueFactory.
final Map<Integer, Group> groupById = ...
final ObservableList<Integer> groupIds = ...
TableColumn<Group, Number> groupCol = new TableColumn<>("Group");
groupCol.setCellValueFactory(cd -> cd.getValue().groupProperty());
class GroupCell extends ListCell<Integer> {
#Override
protected void updateItem(Integer item, boolean empty) {
super.updateItem(item, empty);
Group group = groupById.get(item);
if (empty || group == null) {
setText("");
} else {
setText(group.getName());
}
}
}
groupCol.setCellFactory(col -> new TableCell<Group, Integer>() {
private final ComboBox<Integer> comboBox = new ComboBox<>(groupIds);
private final ChangeListener<Integer> listener = (o, oldValue, newValue) -> {
Group group = (Group) getTableView().getItems().get(getIndex());
group.setGroup(newValue);
};
{
comboBox.setCellFactory(lv -> new GroupCell());
comboBox.setButtonCell(new GroupCell());
}
#Override
protected void updateItem(Number item, boolean empty) {
super.updateItem(item, empty);
if (empty || item == null) {
setGraphic(null);
} else {
comboBox.valueProperty().removeListener(listener);
setGraphic(comboBox);
comboBox.setValue((Integer) item);
comboBox.valueProperty().addListener(listener);
}
}
});

Answer 2

It's a bit hard to tell from only some small code snippets, but my general recommendation when working with frontends is to distinguish between the model and the rendering on each level. This applies to JavaFX, Swing and Angular applications alike.
The appointee TableView should likely be TableView<Appointee>.
For the appointee.group property you have two options: either use Group or (e.g. when this would generate too many duplicate data when de-/serializing from/ to JSON) then use a business key. The first option is usually easier to implement and work with. With the second option you'll need some service / code to convert back to a Group and have to think about where/ at what level exactly you want to do the conversion.
Let's go on here with the second option as you currently have specified appointee.group to be an integer.
In this case the group column should be TableColum<Appointee, Integer>.
The group cell then should be TableCell<Appointee, Integer>.
So far we've only talked about the model, not about rendering except that we want to display the appointees in a table.
I recommend to do this also on the next level.
Don't use a ComboBox<String> for a groups comboBox but a ComboBox<Group>. String is how you want to render the group inside the comboBox but the Group is the model. Also ComboBox<Integer>, the type of the business key, is a bit misleading (as you want a Groups comboBox, not an integer comboBox) and limits the flexibility of your code.
Use the converting service / code I've mentioned when pre-selecting a value in the comboBox.
The group cell should have the type ListCell<Group> and in the updateItem method, which concerns about how to render a Group, you could e.g. use the name property to get the String representation.
Of course there are variations of this approach, but make sure that on each level you know what the model of the control is and what the renderer of the control is. Always design your code using the model and use the rendering types only at the lowest rendering level.