JavaFX：使节点不占用空间，但让其父节点决定其位置

Question

我有一个文本字段和一个列表视图。当用户在文本字段中键入内容时，列表视图中会出现一些建议:

当TextField为空时，通过将可见和托管属性设置为false，ListView将消失。

然而，当用户开始输入时，ListView会占用空间并向下推送所有内容。使用。setManaged(false)允许它不占用任何空间，但它不再显示，因为我还没有为它定义位置。我尝试过设置搜索列表的layoutX和layoutY，但是还是没有显示。

理想情况下，我希望ListView的位置受布局的影响，但不占用任何空间。

有什么想法吗？

Answer 1

将保存文本字段的容器包装在AnchorPane中。将ListView添加到文本字段容器之后的AnchorPane中（因此它保持在顶部）。然后您需要在使其可见时将ListView相对于文本字段适当定位；我认为最好的方法是首先将文本字段的边界从本地坐标转换为Scene坐标，然后将这些边界转换为相对于AnchorPane的坐标。

这里有一个SSCCE:

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.geometry.Bounds;
import javafx.geometry.Insets;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.ListView;
import javafx.scene.control.TextField;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

public class SuggestionList extends Application {

    @Override
    public void start(Stage primaryStage) {
        AnchorPane root = new AnchorPane();

        ListView<String> suggestionBox = new ListView<>();
        suggestionBox.getItems().addAll("Here", "Are", "Some", "Suggestions");
        suggestionBox.setMaxHeight(100);
        suggestionBox.setVisible(false);

        // Grid pane to hold a bunch of text fields:
        GridPane form = new GridPane();
        for (int i=0; i<10; i++) {
            form.addRow(i, new Label("Enter Text:"), createTextField(suggestionBox));
        }

        // just move the grid pane a little to test suggestion box positioning:
        AnchorPane.setLeftAnchor(form, 20.0);
        AnchorPane.setRightAnchor(form, 20.0);
        AnchorPane.setTopAnchor(form, 20.0);
        AnchorPane.setBottomAnchor(form, 20.0);

        // allows focus on grid pane, so user can click on it to remove focus from text field.
        form.setFocusTraversable(true);

        root.setPadding(new Insets(20));

        root.getChildren().addAll(form, suggestionBox);

        Scene scene = new Scene(root, 600, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private TextField createTextField(ListView<String> suggestionBox) {
        TextField textField = new TextField();
        ChangeListener<String> selectionListener = (obs, oldItem, newItem) -> {
            if (newItem != null) {
                textField.setText(newItem);
            }
        };
        textField.focusedProperty().addListener((obs, wasFocused, isNowFocused) -> {
            if (isNowFocused) {
                suggestionBox.setVisible(true);

                // compute bounds of text field relative to suggestion box's parent:
                Parent parent = suggestionBox.getParent(); // (actually the anchor pane)
                Bounds tfBounds = textField.getBoundsInLocal();
                Bounds tfBoundsInScene = textField.localToScene(tfBounds);
                Bounds tfBoundsInParent = parent.sceneToLocal(tfBoundsInScene);

                // position suggestion box:
                suggestionBox.setLayoutX(tfBoundsInParent.getMinX());
                suggestionBox.setLayoutY(tfBoundsInParent.getMaxY());
                suggestionBox.setPrefWidth(tfBoundsInParent.getWidth());

                suggestionBox.getSelectionModel().selectedItemProperty().addListener(selectionListener);
            } else {
                suggestionBox.setVisible(false);
                suggestionBox.getSelectionModel().selectedItemProperty().removeListener(selectionListener);
            }
        });
        textField.setOnAction(event -> {
            suggestionBox.setVisible(false);
            suggestionBox.getSelectionModel().selectedItemProperty().removeListener(selectionListener);         
        });
        return textField ;
    }

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

您可能能够使用类似的位置技巧，只需将它添加到同一个场景中，并将< code>managed设置为false。