How to get an auto-sorting TableView? - javafx

Question

I have a TableView with a list of items (Transaction) and want it to sort, so that all positive values are above the negative ones. This is the only requirement.
What I have until now:
expensesTableView.sortPolicyProperty().set(
new Callback<TableView<Transaction>, Boolean>() {
#Override
public Boolean call(TableView<Transaction> param) {
Comparator<Transaction> c = (a, b) -> {
if (a.getValue().contains("-") ^ b.getValue().contains("-")) { //getValue() returns a String
return a.getValue().contains("-") ? 1 : -1;
}
return 0;
};
FXCollections.sort(expensesTableView.getItems(), c);
return true;
};
});
This wasn't my idea, I found this on the net, so don't ask if it looks like a strange way to achieve that. The real problem is, that the table doesn't sort on its own when a new item is added/edited/deleted. I need to click the header 3 times and then it does what I want.
How can I have a list that is always sorted correctly?
I tried adding a ChangeListener and sort on change. But besides that this is an ugly way to do that, it didn't even work... I'm at the end of ideas.

Answer 1

The bitwise OR in the comparator didn't work in my tests, so I've changed it to a normal one, and it's also not checking for change in the value of items from the list.
I wonder if it might be more efficient to do a numeric check rather than a String check, negatives could still sort out below, but I guess the conversion might cost more?
My first idea with SortedList in the comments was actually related to keeping the original sorted order, to be restored after the user has changed the sort, so was off the mark.
Edited to add: Just to clarify, it's the act of keeping the source list sorted that keeps the table list sorted.
public class TestApp extends Application {
private int c;
private ObservableList<TestTransaction> sortedOL;
private final Comparator<TestTransaction> comp = (TestTransaction a, TestTransaction b) -> {
if (a.getValue().contains("-") || b.getValue().contains("-")) {
return a.getValue().contains("-") ? 1 : -1;
}
return 0;
};
private TableView<TestTransaction> tableView;
#Override
public void start(Stage primaryStage) {
ArrayList<TestTransaction> rawList = new ArrayList<>();
for (int i = 1; i < 20; i++) {
int v = i * 3;
if (v % 2 > 0) {
v = v * -1;
}
c = i;
rawList.add(new TestTransaction(Integer.toString(v), "Item " + c));
}
sortedOL = FXCollections.observableArrayList(rawList);
sortedOL.addListener((ListChangeListener.Change<? extends TestTransaction> c1) -> {
if (c1.next() && (c1.wasAdded() || c1.wasRemoved())) {
FXCollections.sort(sortedOL, comp);
}
});
FXCollections.sort(sortedOL, comp);
tableView = new TableView<>(sortedOL);
TableColumn<TestTransaction,String> valCol = new TableColumn<>("Value");
valCol.setCellValueFactory(new PropertyValueFactory("value"));
TableColumn<TestTransaction,String> nameCol = new TableColumn<>("Name");
nameCol.setCellValueFactory(new PropertyValueFactory("name"));
tableView.getColumns().setAll(valCol, nameCol);
BorderPane tpane = new BorderPane();
Button btnAdd = new Button("Add");
btnAdd.setOnAction(a -> {addTransaction();});
ToolBar tb = new ToolBar(btnAdd);
tpane.setTop(tb);
tpane.setCenter(tableView);
tpane.setPrefSize(600, 600);
Scene scene = new Scene(tpane, 600, 600);
primaryStage.setTitle("Test");
primaryStage.setScene(scene);
primaryStage.show();
}
private void addTransaction() {
c++;
int v = (int) Math.floor(Math.random() * 50);
if (v % 2 > 0) {
v = v * -1;
}
sortedOL.add(new TestTransaction(Integer.toString(v), "New Item " + c));
}
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
launch(args);
}
}
public class TestTransaction {
private String value;
private String name;
public TestTransaction(String value, String name) {
this.value = value;
this.name = name;
}
/**
* #return the value
*/
public String getValue() {
return value;
}
/**
* #return the name
*/
public String getName() {
return name;
}
}
If you want to use SortedList, meaning you could inline the comparator:
sortedOL = FXCollections.observableArrayList(rawList);
SortedList sorted = new SortedList(sortedOL, comp);
tableView = new TableView<>(sorted);