ScrollPane 未按需显示，FlowPane 内容

Question

我在使用 JavaFX 8 中的 ScrollPane 根据需要显示滚动条时遇到了一些困难。我目前正在做的只是创建一个包含 x 个元素的 FlowPane，并将其设置为 ScrollPane 的内容。

当我垂直于 FlowPane 的方向缩小时出现问题。当元素开始换行并越界时，滚动条不会出现。当我平行于方向收缩时，这不会发生。我有一个小的 Java 程序来举例说明这个问题。

Start

Shrinking Parallel

Shrinking Perpendicular

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.FlowPane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class Main extends Application {

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

       @Override
       public void start(Stage primaryStage) throws Exception {
             FlowPane flow = new FlowPane();
             flow.setStyle("-fx-border-color: red");
             addPanes(flow, 16);

             ScrollPane scroll = new ScrollPane(flow);
             scroll.setStyle("-fx-border-color: green");
             scroll.setFitToHeight(true);
             scroll.setFitToWidth(true);

             Scene scene = new Scene(scroll, 450, 450);
             primaryStage.setScene(scene);
             primaryStage.show();
       }

       public void addPanes(FlowPane root, int panes) {
             for(int i = 0; i < panes; i++) {
                    StackPane filler = new StackPane();
                    filler.setStyle("-fx-border-color: black");
                    filler.setPrefSize(100, 100);
                    root.getChildren().add(filler);
             }
       }
}

Answer 1

看看下面的代码，告诉我这是否是您想要实现的。我仍然不确定是什么导致了这个问题，我将不得不查看 ScrollPane 的文档来找出答案。我怀疑是 setFitToWidth & setFitToHeight 方法。虽然我仍然相信这不是一个错误。

import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.FlowPane;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class Main extends Application {

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        FlowPane flow = new FlowPane();
        flow.setStyle("-fx-border-color: red");

        addPanes(flow, 16);

        ScrollPane scroll = new ScrollPane(flow);
        scroll.setStyle("-fx-border-color: green");

        // Apparently this cause the issue here.
        // scroll.setFitToHeight(true);
        // scroll.setFitToWidth(true);


        // Instead just make the flow pane take the dimensions of the ScrollPane
        // the -5 is to not show the Bars when both of panes have the same dimensions  
        flow.prefWidthProperty().bind(Bindings.add(-5, scroll.widthProperty()));
        flow.prefHeightProperty().bind(Bindings.add(-5, scroll.heightProperty()));

        Scene scene = new Scene(scroll, 450, 450);
        primaryStage.setScene(scene);
        primaryStage.show();

    }

    public void addPanes(FlowPane root, int panes) {
        for (int i = 0; i < panes; i++) {
            HBox filler = new HBox();
            filler.setStyle("-fx-border-color: black");
            filler.setPrefSize(100, 100);
            root.getChildren().add(filler);
        }
    }
}

查看 ScrollPane 的文档，特别是 setFitToHeight 您会发现：

Property description: If true and if the contained node is a Resizable, then the node will be kept resized to match the height of the ScrollPane's viewport. If the contained node is not a Resizable, this value is ignored.

并且由于 ScrollPane 内的节点将保持调整大小以匹配 ScrollPane 视口的宽度和高度，这就是 Vertical ScrollBar 永远不会出现的原因。

Answer 2

您可以添加以下代码以始终显示垂直滚动条。

scroll.setVbarPolicy(ScrollPane.ScrollBarPolicy.ALWAYS);

Answer 3

当计算出 ScrollPane 内 FlowPane 所需的高度时，将传递宽度值 -1。当所有内容都适合一行时，流程窗格将报告所需的高度。

在这种情况下，作为解决方法，您可以传递上次布局计算的宽度。

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.FlowPane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class Main extends Application {

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

       @Override
       public void start(Stage primaryStage) throws Exception {
             FlowPane flow = new FlowPane() {
                @Override protected double computeMinHeight(double width) {
                    double minHeight = super.computeMinHeight(width != -1 ? width : 
                        /* When no width is specified, use the current contol size*/ 
                        getWidth());
                    return minHeight;
                }
             };
             flow.setStyle("-fx-border-color: red");
             addPanes(flow, 16);

             ScrollPane scroll = new ScrollPane(flow);
             flow.maxWidthProperty().bind(scroll.widthProperty());
             scroll.widthProperty().addListener((observable, oldValue, newValue)->{
                 /* clearSizeCache */
                 flow.requestLayout();
             });

             scroll.setStyle("-fx-border-color: green");
             scroll.setFitToHeight(true);
             scroll.setFitToWidth(true);

             Scene scene = new Scene(scroll, 450, 450);
             primaryStage.setScene(scene);
             primaryStage.show();
       }

       public void addPanes(FlowPane root, int panes) {
             for(int i = 0; i < panes; i++) {
                    StackPane filler = new StackPane();
                    filler.setStyle("-fx-border-color: black");
                    filler.setPrefSize(100, 100);
                    root.getChildren().add(filler);
             }
       }
}

ScrollPane 未按需显示，FlowPane 内容

ScrollPane not showing as needed, FlowPane content

java

javafx

scrollpane

flowpane

javafx-8