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在这个问题中，我展示了如何通过更改其包装对象而不发送它更改的更新来处理属性更改的问题。一个解决方案是使用 ReactFX：

class Cell {

    private final ObjectProperty<Shape> shape = new SimpleObjectProperty<>(new Shape());
    // all getters and setterts

    public static class Shape {

        private final IntegerProperty size = new SimpleIntegerProperty(0);
        // all getters and setterts
    }

    public static void main(String[] args) {

        Var<Number> sizeVar = Val.selectVar(cell.shapeProperty(), Shape::sizeProperty);
        sizeVar.addListener(
            (obs, oldSize, newSize) -> System.out.println("Size changed from "+oldSize+" to "+newSize));
}

所以现在如果shape属性本身发生变化，它也会触发变化size（除非新形状具有相同的大小）。但现在我想用自定义绑定绑定到属性，我有一个问题解释如下。

我的数据类是这些：

class Cell {

    private final ObjectProperty<Shape> shape = new SimpleObjectProperty<>();
    public final ObjectProperty<Shape> shapeProperty() { return shape; }
    public final Shape getShape()                      { return shapeProperty().get(); }
    public final void setShape(Shape shape)            { shapeProperty().set(shape); }

    // other properties
}

class Shape {

    private final IntegerProperty size = new SimpleIntegerProperty();
    public final IntegerProperty sizeProperty() { return size; }
    public final int getSize()                  { return size.get(); }
    public final void setSize(int size)         { sizeProperty().set(size); }

    // other properties
}

我想通过将它们的属性绑定到 GUI 属性来为它们创建一个 GUI 表示。我这样做：

class CellRepresentation extends Group {

    private final Cell cell;

    CellRepresentation(Cell cell) {

        this.cell = cell;
        getChildren().add(new ShapeRepresentation() /*, other representations of things in the cell*/);
    }

    private class ShapeRepresentation extends Cylinder {

        ObjectProperty<Shape> shape;

        private ShapeRepresentation() {

            super(100, 100);

            shape = new SimpleObjectProperty<Shape>(cell.getShape());
            shape.bind(cell.shapeProperty());

            Var<Number> sizeVar = Val.selectVar(cell.shapeProperty(), Shape::sizeProperty);

            // THIS WILL WORK
            materialProperty().bind(Bindings.createObjectBinding(() -> {
                if (shape.get() == null)
                    return new PhongMaterial(Color.TRANSPARENT);
                return new PhongMaterial(Color.RED);
            }, sizeVar));

            // THIS WILL NOT WORK
            materialProperty().bind(sizeVar.map(n -> {
                if (shape.get() == null)
                    return new PhongMaterial(Color.TRANSPARENT);
                return new PhongMaterial(Color.RED);
            }));
        }
    }

    // the other representations of things in the cell
}

当我运行下面的第一个绑定选项的代码时，将创建一个透明圆柱体。第二个选项将创建一个白色（默认颜色）圆柱体。我不知道为什么会这样。

public class Example extends Application {

    public static void main(String[] args) {

        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {

        Cell cell = new Cell();
        CellRepresentation cellRep = new CellRepresentation(cell);

        Group group = new Group(cellRep);
        Scene scene = new Scene(group, 200, 200, Color.AQUA);
        stage.setScene(scene);
        stage.show();
    }
}

如果这不是使用绑定为数据类创建表示的好方法，我也愿意接受设计建议。

4

1 回答 1

2

Val并且Var是“可观察的单子”（想想 observable Optionals）。它们要么是空的，要么是有值的。该map方法的工作原理类似于Optional.map：如果Val为空，则map结果为空Val；否则，它会导致Val包含将函数应用于原始Val值的结果。因此，如果sizeVar计算结果为null，则映射结果为空Val（因此您的材料设置为null），甚至没有计算您的 lambda 表达式。

要处理null（即空Vals），您应该使用orElse或类似的方法：

private class ShapeRepresentation extends Cylinder {

    Val<Shape> shape;

    private ShapeRepresentation() {

        super(100, 100);

        shape = Val.wrap(cell.shapeProperty());

        Var<Number> sizeVar = shape.selectVar(Shape::sizeProperty);

        // THIS WILL WORK

        materialProperty().bind(shape
            .map(s -> new PhongMaterial(Color.RED))
            .orElseConst(new PhongMaterial(Color.TRANSPARENT)));

        // SO WILL THIS

        materialProperty().bind(sizeVar
                .map(n -> {
                    if (n.intValue() == 1) return new PhongMaterial(Color.RED) ;
                    if (n.intValue() == 2) return new PhongMaterial(Color.BLUE) ;
                    return new PhongMaterial(Color.WHITE);
                })
                .orElseConst(new PhongMaterial(Color.TRANSPARENT)));

    }
}

更新的测试示例：

import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.geometry.Insets;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.CheckBox;
import javafx.scene.control.ComboBox;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class Example extends Application {

    public static void main(String[] args) {

        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {

        Cell cell = new Cell();

        CellRepresentation cellRep = new CellRepresentation(cell);

        Group group = new Group(cellRep);

        ComboBox<Integer> sizeCombo = new ComboBox<>();
        sizeCombo.getItems().addAll(0, 1, 2);

        Shape shape = new Shape();
        shape.sizeProperty().bind(sizeCombo.valueProperty());


        CheckBox showShape = new CheckBox("Show shape");
        cell.shapeProperty().bind(Bindings.when(showShape.selectedProperty()).then(shape).otherwise((Shape)null));

        HBox controls = new HBox(5, showShape, sizeCombo);
        controls.setPadding(new Insets(5));

        BorderPane root = new BorderPane(group, controls, null, null, null);
        root.setBackground(null);

        Scene scene = new Scene(root, 400, 400, Color.AQUA);
        stage.setScene(scene);
        stage.show();
    }
}
于 2017-01-11T01:04:14.000 回答