JavaFx Bindings: is there a way to bind a value to an observable list?

Question

I have a table view whose contents are an observable list that contains numbers, and I have a text field that should display the sum of these values ​​in the table, is there any way to bind these text fields to the sum of the properties of the number. note: the user can edit the values ​​in this list, can add more elements, can delete any element, how can I link the sum of these numbers correctly using javafx binding, instead of doing it according to the old way of iterating over the list and summing the numbers manually, and each change is repeated again.

Answer 1

ObservableListwill update events if (and only if) you create a list using an extractor . An extractor is a function that maps each element of a list to an array Observables ; if any of these Observablechanges their value, the list triggers the corresponding update events and becomes invalid.

So, two steps:

• Create a list using an extractor
• Create a binding that calculates the total whenever the list is not valid.

So, if you have a model class for your table, for example:

public class Item {

    private final IntegerProperty value = new SimpleIntegerProperty();

    public IntegerProperty valueProperty() {
        return value ;
    }

    public final int getValue() {
        return valueProperty().get();
    }

    public final void setValue(int value) {
        valueProperty().set(value);
    }

    // other properties, etc...
}

Then you create the table with:

TableView<Item> table = new TableView<>();
table.setItems(FXCollections.observableArrayList(item -> 
    new Observable[] { item.valueProperty() }));

Now you can create a binding using

IntegerBinding total = Bindings.createIntegerBinding(() ->
    table.getItems().stream().collect(Collectors.summingInt(Item::getValue)),
    table.getItems());

: createIntegerBinding - , int . - ( , table.getItems()) , . , table.getItems(), , - valueProperty() . , , - API- Java 8 Streams,

() -> {
    int totalValue = 0 ;
    for (Item item : table.getItems()) {
        totalValue = totalValue + item.getValue();
    }
    return totalValue ;
}

, , , -

Label totalLabel = new Label();
totalLabel.textProperty().bind(Bindings.format("Total: %d", total));

SSCCE:

import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

import javafx.application.Application;
import javafx.beans.Observable;
import javafx.beans.binding.Bindings;
import javafx.beans.binding.IntegerBinding;
import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.beans.value.ObservableValue;
import javafx.collections.FXCollections;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.TextFieldTableCell;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Priority;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.util.StringConverter;
import javafx.util.converter.DefaultStringConverter;
import javafx.util.converter.NumberStringConverter;

public class TotallingTableView extends Application {

    @Override
    public void start(Stage primaryStage) {

        TableView<Item> table = new TableView<>();
        table.setEditable(true);

        table.getColumns().add(
                column("Item", Item::nameProperty, new DefaultStringConverter()));

        table.getColumns().add(
                column("Value", Item::valueProperty, new NumberStringConverter()));

        table.setItems(FXCollections.observableArrayList(
                item -> new Observable[] {item.valueProperty() }));

        IntStream.rangeClosed(1, 20)
            .mapToObj(i -> new Item("Item "+i, i))
            .forEach(table.getItems()::add);

        IntegerBinding total = Bindings.createIntegerBinding(() -> 
            table.getItems().stream().collect(Collectors.summingInt(Item::getValue)),
            table.getItems());

        Label totalLabel = new Label();
        totalLabel.textProperty().bind(Bindings.format("Total: %d", total));

        Button add = new Button("Add item");
        add.setOnAction(e -> 
            table.getItems().add(new Item("New Item", table.getItems().size() + 1)));

        Button remove = new Button("Remove");
        remove.disableProperty().bind(
                Bindings.isEmpty(table.getSelectionModel().getSelectedItems()));

        remove.setOnAction(e -> 
            table.getItems().remove(table.getSelectionModel().getSelectedItem()));

        HBox buttons = new HBox(5, add, remove);
        buttons.setAlignment(Pos.CENTER);
        VBox controls = new VBox(5, totalLabel, buttons);
        VBox.setVgrow(totalLabel, Priority.ALWAYS);
        totalLabel.setMaxWidth(Double.MAX_VALUE);
        totalLabel.setAlignment(Pos.CENTER_RIGHT);

        BorderPane root = new BorderPane(table, null, null, controls, null);
        Scene scene = new Scene(root, 800, 600);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private <S,T> TableColumn<S,T> column(String title, 
            Function<S, ObservableValue<T>> property, StringConverter<T> converter) {
        TableColumn<S,T> col = new TableColumn<>(title);
        col.setCellValueFactory(cellData -> property.apply(cellData.getValue()));

        col.setCellFactory(TextFieldTableCell.forTableColumn(converter));

        return col ;
    }

    public static class Item {
        private final StringProperty name = new SimpleStringProperty();
        private final IntegerProperty value = new SimpleIntegerProperty();

        public Item(String name, int value) {
            setName(name);
            setValue(value);
        }

        public final StringProperty nameProperty() {
            return this.name;
        }

        public final java.lang.String getName() {
            return this.nameProperty().get();
        }

        public final void setName(final java.lang.String name) {
            this.nameProperty().set(name);
        }

        public final IntegerProperty valueProperty() {
            return this.value;
        }

        public final int getValue() {
            return this.valueProperty().get();
        }

        public final void setValue(final int value) {
            this.valueProperty().set(value);
        }


    }

    public static void main(String[] args) {
        launch(args);
    }
}

, , , (IMHO) . , . / . , , , . , value . , .

Answer 2

ObservableList .

list.addListener((obs, oldValue, newValue) -> {  
    textfield.setText(list.stream().mapToInt(x -> x.intValue()).sum(); 
});

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