JavaFX:getWidth() 和 getLayoutBounds() 返回 0

Question

大家好，我正在开发一个简单的编辑器来使用 JavaFX 创建一些用例。现在，当我想将两个节点相互连接时，我想为该链接指定一个名称。目前的想法是将标签放入 anchor Pane 中，并将该 Pane 置于链接的中间。问题是， getWidth() 和 getLayoutBounds() 函数都返回正确的结果，但在所有情况下都返回 0。我怎样才能算出该anchorPane的宽度？感谢您的所有回答!

//Java代码

public class Link extends AnchorPane{

    public Link() {
        FXMLLoader fxmlLoader = new FXMLLoader(
            getClass().getResource("../view/Link.fxml")
        );

        fxmlLoader.setRoot(this); 
        fxmlLoader.setController(this);

        try { 
            fxmlLoader.load();

        } catch (IOException exception) {
            throw new RuntimeException(exception);
        }
    }

    public void bindAnchorPane(DraggableNode source, DraggableNode target){
        //Middlepoint X source and target node
        NumberBinding middleX = Bindings.add(Bindings.divide(source.layoutXProperty(), 2), Bindings.add(Bindings.divide(target.layoutXProperty(), 2), source.getWidth() / 2.0));
        //Middlepoint Y source and target node
        NumberBinding middleY = Bindings.add(Bindings.divide(source.layoutYProperty(), 2), Bindings.add(Bindings.divide(target.layoutYProperty(), 2), source.getWidth() / 2.0));

        //X position of the anchorPane
        //Middlepoint X - anchor.getWidth()/2
        NumberBinding coordX = Bindings.subtract(middleX, anchor_link_label.getWidth()/2;
//        Bounds bounds = anchor_link_label.getLayoutBounds();
//        NumberBinding coordX = Bindings.subtract(middleX, (bounds.getMaxX() - bounds.getMinX()));

        anchor_link_label.layoutXProperty().bind(coordX);
        anchor_link_label.layoutYProperty().bind(middleY);

    }
}

//FXML文件

<fx:root stylesheets="@application.css" type="Pane" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1">
       <children>
            <CubicCurve fx:id="node_link" controlX2="50.0" controlY1="10.0" controlY2="10.0" endX="10.0" fill="#1f93ff00" stroke="BLACK" />
            <AnchorPane fx:id="anchor_link_label" managed="false">
                <Label fx:id="label_link" text="" onMouseClicked="#showTextField" visible="false" managed="false"/>
                <TextField fx:id="textField_link" minWidth="100" visible="true" managed="true"/>
            </AnchorPane>
       </children>
    </fx:root>

Answer 1

在这段代码运行时，高度和宽度为零，因为我猜测节点尚未布局。

如果您希望 middleX、middleY 和 coordX 绑定(bind)更新为当前宽度/高度，那么您需要将它们绑定(bind)到宽度高度属性/绑定(bind)，而不仅仅是您在零时进行“source.getWidth()/2.0”调用时的宽度/高度。

试试这个:

// Middlepoint X source and target node
NumberBinding middleX = source.layoutXProperty().divide(2)
        .add(target.layoutXProperty().divide(2).add(source.widthProperty().divide(2)));

// Middlepoint Y source and target node
NumberBinding middleY = source.layoutYProperty().divide(2)
        .add(target.layoutYProperty().divide(2).add(source.heightProperty().divide(2)));

// X position of the anchorPane
// Middlepoint X - anchor.getWidth()/2
NumberBinding coordX = middleX.subtract(anchor_link_label.widthProperty().divide(2));

// anchor_link_label.layoutXProperty().bind(coordX);
// anchor_link_label.layoutYProperty().bind(middleY);

// To avoid binding and getting a "bound value cannot be set" error
// you can just use listeners instead.

// However, this is slightly hackish, since you are re-laying-out this child 
// after the parent tries to lay it out already.
// What you probably should do is define a parent that overrides 
// `layoutChildren()` and determines how to layout this node.

// Here are the listeners:
coordX.addListener((obs, oldVal, newVal) -> {
    anchor_link_label
        .setLayoutX(
            newVal.doubleValue() - anchor_link_label.getLayoutBounds().getMinX());
    });

middleY.addListener((obs, oldVal, newVal) -> {
    anchor_link_label
        .setLayoutY(
             newVal.doubleValue() - anchor_link_label.getLayoutBounds().getMinY());
    });

一个可能的替代方案是使用 HBox 作为您的父级并将对齐方式设置为居中，而不是使用通用 Pane，因为这似乎是您真正想要的它要做的就是将标签放在 Pane 的中央。