我的一个JavaFX项目有一个设置窗口，其中包含一个ScrollPane。我有所有的复选框，输入字段和滑块。
<?xml version="1.0" encoding="UTF-8"?>
<?import com.jfoenix.controls.JFXCheckBox?>
<?import com.jfoenix.controls.JFXComboBox?>
<?import com.jfoenix.controls.JFXSlider?>
<?import com.jfoenix.controls.JFXTabPane?>
<?import com.jfoenix.controls.JFXTextField?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.ScrollPane?>
<?import javafx.scene.control.Tab?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.layout.StackPane?>
<?import javafx.scene.layout.VBox?>
<StackPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.65" xmlns:fx="http://javafx.com/fxml/1">
<children>
<JFXTabPane rotateGraphic="true" side="BOTTOM">
<tabs>
<Tab closable="false" styleClass="container" text="%settings.tab.main">
<content>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="20.0" styleClass="container">
<children>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="15.0">
<children>
<Label maxWidth="1.7976931348623157E308" text="%settings.language" />
<JFXComboBox maxWidth="1.7976931348623157E308" promptText="%settings.language" />
</children>
</VBox>
<VBox layoutX="10.0" layoutY="10.0" prefHeight="200.0" prefWidth="100.0" spacing="15.0">
<children>
<Label maxWidth="1.7976931348623157E308" text="%settings.window.width" />
<JFXSlider majorTickUnit="50.0" max="1049.0" maxWidth="1.7976931348623157E308" min="850.0" minorTickCount="10" showTickLabels="true" showTickMarks="true" />
</children>
</VBox>
<VBox layoutX="10.0" layoutY="210.0" prefHeight="200.0" prefWidth="100.0" spacing="15.0">
<children>
<Label maxWidth="1.7976931348623157E308" text="%settings.window.height" />
<JFXSlider majorTickUnit="50.0" max="900.0" maxWidth="1.7976931348623157E308" min="500.0" minorTickCount="10" showTickLabels="true" showTickMarks="true" />
</children>
</VBox>
<VBox layoutX="10.0" layoutY="143.0" prefHeight="200.0" prefWidth="100.0" spacing="15.0">
<children>
<JFXCheckBox maxWidth="1.7976931348623157E308" text="%settings.window.maximized" />
</children>
</VBox>
</children>
<padding>
<Insets bottom="30.0" left="30.0" right="30.0" top="30.0" />
</padding>
</VBox>
</content>
</Tab>
<Tab closable="false" styleClass="container" text="%settings.tab.exercises">
<content>
<ScrollPane fitToHeight="true" fitToWidth="true" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" prefViewportHeight="593.0" prefViewportWidth="600.0">
<content>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="20.0" styleClass="container">
<children>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="10.0">
<children>
<Label maxWidth="1.7976931348623157E308" text="%settings.add.ex" />
<HBox maxWidth="1.7976931348623157E308" prefHeight="100.0" prefWidth="200.0">
<children>
<JFXCheckBox maxHeight="30.0" maxWidth="1.7976931348623157E308" prefWidth="150.0" text="%settings.add" HBox.hgrow="ALWAYS" />
<JFXTextField maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.add.min" HBox.hgrow="ALWAYS" />
<JFXTextField maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.add.max" HBox.hgrow="ALWAYS" />
</children>
</HBox>
</children>
</VBox>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="10.0">
<children>
<Label maxWidth="1.7976931348623157E308" text="%settings.sub.ex" />
<HBox maxWidth="1.7976931348623157E308" prefHeight="100.0" prefWidth="200.0">
<children>
<JFXCheckBox maxHeight="30.0" maxWidth="1.7976931348623157E308" prefWidth="150.0" text="%settings.sub" HBox.hgrow="ALWAYS" />
<JFXTextField maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.sub.min" HBox.hgrow="ALWAYS" />
<JFXTextField maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.sub.max" HBox.hgrow="ALWAYS" />
</children>
</HBox>
</children>
</VBox>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="10.0">
<children>
<Label maxWidth="1.7976931348623157E308" text="%settings.mul.ex" />
<HBox maxWidth="1.7976931348623157E308" prefHeight="100.0" prefWidth="200.0">
<children>
<JFXCheckBox maxHeight="30.0" maxWidth="1.7976931348623157E308" prefWidth="150.0" text="%settings.mul" HBox.hgrow="ALWAYS" />
<JFXTextField maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.mul.min" HBox.hgrow="ALWAYS" />
<JFXTextField maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.mul.max" HBox.hgrow="ALWAYS" />
</children>
</HBox>
</children>
</VBox>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="10.0">
<children>
<Label maxWidth="1.7976931348623157E308" text="%settings.div.ex" />
<HBox maxWidth="1.7976931348623157E308" prefHeight="100.0" prefWidth="200.0">
<children>
<JFXCheckBox maxHeight="30.0" maxWidth="1.7976931348623157E308" prefWidth="150.0" text="%settings.div" HBox.hgrow="ALWAYS" />
<JFXTextField maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.div.min" HBox.hgrow="ALWAYS" />
<JFXTextField maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.div.max" HBox.hgrow="ALWAYS" />
</children>
</HBox>
</children>
</VBox>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="10.0">
<children>
<Label disable="true" maxWidth="1.7976931348623157E308" text="%settings.power.ex" />
<HBox maxWidth="1.7976931348623157E308" prefHeight="100.0" prefWidth="200.0">
<children>
<JFXCheckBox disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" prefWidth="150.0" text="%settings.power" HBox.hgrow="ALWAYS" />
<JFXTextField disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.power.min.base" HBox.hgrow="ALWAYS" />
<JFXTextField disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.power.max.base" HBox.hgrow="ALWAYS" />
</children>
</HBox>
</children>
</VBox>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="10.0">
<children>
<Label disable="true" maxWidth="1.7976931348623157E308" text="%settings.roots.ex" />
<HBox maxWidth="1.7976931348623157E308" prefHeight="100.0" prefWidth="200.0">
<children>
<JFXCheckBox disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" prefWidth="150.0" text="%settings.roots" HBox.hgrow="ALWAYS" />
<JFXTextField disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.roots.min.rad" HBox.hgrow="ALWAYS" />
<JFXTextField disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.roots.max.rad" HBox.hgrow="ALWAYS" />
</children>
</HBox>
<HBox layoutX="10.0" layoutY="37.0" maxWidth="1.7976931348623157E308" prefHeight="100.0" prefWidth="200.0">
<children>
<JFXCheckBox disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" prefWidth="150.0" text="%settings.roots.dec" HBox.hgrow="ALWAYS" />
<JFXTextField disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.roots.min.expo" HBox.hgrow="ALWAYS" />
<JFXTextField disable="true" maxHeight="30.0" maxWidth="1.7976931348623157E308" promptText="%settings.roots.max.expo" HBox.hgrow="ALWAYS" />
</children>
</HBox>
</children>
</VBox>
<VBox prefHeight="200.0" prefWidth="100.0" spacing="10.0">
<children>
<Label maxWidth="1.7976931348623157E308" text="%settings.count" />
</children>
</VBox>
</children>
<padding>
<Insets bottom="20.0" left="20.0" right="20.0" top="20.0" />
</padding>
</VBox>
</content>
</ScrollPane>
</content>
</Tab>
</tabs>
</JFXTabPane>
</children>
<padding>
<Insets top="50.0" />
</padding>
</StackPane>
要设置这些节点的默认值，我希望Java代码使用其FX：ID访问每个元素。
package handlers;
import java.io.IOException;
import com.jfoenix.controls.JFXCheckBox;
import com.jfoenix.controls.JFXComboBox;
import com.jfoenix.controls.JFXSlider;
import com.jfoenix.controls.JFXSnackbar;
import com.jfoenix.controls.JFXTextField;
import initializers.InitSettings;
import javafx.fxml.FXML;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import resources.lang.Locales;
import settings.Settings;
import resources.lang.Language;
public class SettingsHandler {
private static Scene scene;
public static void setDefault(Scene scene) {
SettingsHandler.scene = scene;
// Replace the checkboxes' values with the values from the settings file (true or false)
setCheckboxValue("add", Settings.add);
setCheckboxValue("sub", Settings.sub);
setCheckboxValue("mul", Settings.mul);
setCheckboxValue("div", Settings.div);
setCheckboxValue("subNeg", Settings.subNeg);
setCheckboxValue("divDec", Settings.divComma);
setCheckboxValue("windowMaximized", Settings.startMaximized);
setCheckboxValue("automaticUpdates", Settings.automaticUpdates);
private static void setCheckboxValue(String selector, boolean value) {
((JFXCheckBox) scene.lookup("#" + selector)).setSelected(value);
}
}
但是Java无法找到元素。
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at handlers.SettingsHandler.setCheckboxValue(SettingsHandler.java:141)
at handlers.SettingsHandler.setDefault(SettingsHandler.java:30)
at initializers.InitSettings.init(InitSettings.java:25)
at initializers.InitMain$2.handle(InitMain.java:66)
at initializers.InitMain$2.handle(InitMain.java:60)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8411)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$355(GlassViewEventHandler.java:388)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
我在Google上的所有搜索查询都无法向我提供正确的信息。我刚刚得到了关于如何创建ScrollPane的更多教程。所以我问你：如何访问ScrollPane中的元素。
答案 0 :(得分：0)
内容图尚未添加到场景图中，因为ScrollPane尚未布局，因此将skin内容添加到场景图中的ScrollPane没有尚未创建。
此代码演示了此行为：
@Override
public void start(Stage primaryStage) {
Rectangle content = new Rectangle(100, 100);
content.setId("id");
ScrollPane sp = new ScrollPane(content);
System.out.println("before: "+sp.lookup("#id")); // null
Scene scene = new Scene(sp);
// do layout (sp needs to be added to a scene for this to work)
sp.applyCss();
sp.layout();
System.out.println("after: "+sp.lookup("#id")); // non-null
primaryStage.setScene(scene);
primaryStage.show();
}
无论如何，在大多数情况下使用lookup识别节点是一个坏主意。更好地使用控制器或至少使用FXMLLoader实例的namespace来加载fxml以使用fx:id来访问对象。
注意：在fxml文件中实际指定fx:id属性也可能会有所帮助。否则即使在布局后你也找不到任何匹配。