问题描述
在我的 gluon Mobile 项目中，我希望允许用户从亮模式切换到暗模式。但是，正如我通过堆栈问题发现的：Allowing user to switch between light and dark mode Gluon，我需要通过 getScene() 方法访问场景。一切正常，直到我尝试将用户首选项保存在每个用户会话的数据文件中；它不再起作用。我不仅收到错误（见下文），而且也没有显示正确的用户首选项（它只显示默认值，直到我使用应用程序内按钮更改它）。目标是让用户能够按下应用内按钮来更改模式，并在用户下次打开应用时自动显示该模式。我知道这是我的项目的一个特定问题，可能不适合 Stack Overflow，但我不知道我还能如何解决这个问题。因此，如果有人可以帮助我，我将不胜感激。我几乎完成了我的应用程序，我有点时间紧迫。非常感谢您抽出宝贵时间，我期待着您的回音。
附注如果您需要此项目的 GitHub 存储库链接，请告诉我。
正在会话类中保存的布尔灯（模式指示器）的（相关部分）代码：
public class Session implements Serializable {
/**
* Data field: userid user name
* Data field: password user password
* Data field: date the date and time the session started
* Data field: feeling1 mood (1..100) of user at the beginning of session
* Data field: feeling2 mood (1..100) of user at the end of session
* Data field: conversation sentences expressed by the user during a session
*/
private String userid = "";
private String password = "";
private boolean light = true;
private Date date = new Date();
private Date time = new Date();
private double feeling1 = 0;
private double feeling2 = 0;
private ArrayList<String> conversation = new ArrayList<>();
private ArrayList<String> times = new ArrayList<>();
private static final long serialVersionUID = 2L;
/**
* The only constructor: It receives a user's id and password
* and starts a session associated with the user. It records
* the date and time the session started.
*
* @param id user id
* @param pass user password
*/
public Session(String id,String pass) {
userid = id;
password = pass;
date = new Date();
}
/**
* Reset mode of user for this session: The method receives a mode (light or dark)
* and replaces current mode with the received mode.
*
* @param dark the new mode
*/
public void setMode(boolean dark) {
light = dark;
}
/**
* Get mode (light or dark) of the user for this session
*
* @return mode of user for this session
*/
public boolean getMode() {
return light;
}
// Use a GridPane to create a login interface insights
VBox grid = new VBox();
//grid.setStyle("-fx-background-color: black;");
grid.setAlignment(Pos.CENTER);
Insets snI = new Insets(10,10,10);
grid.setPadding(snI);
Button button = new Button();
grid.getChildren().add(button);
if (session.getMode() == true) {
light = true;
LIGHT.assignTo(grid.getScene()); // ERROR IS POINTING TO THIS LINE
button.setGraphic(new Icon(MaterialDesignIcon.BRIGHTnesS_2));
} else if (session.getMode() == false) {
light = false;
DARK.assignTo(grid.getScene());
button.setGraphic(new Icon(MaterialDesignIcon.WB_SUNNY));
}
错误本身：
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException: Scene cannot be null
at java.base/java.util.Objects.requireNonNull(Objects.java:246)
at com.gluonhq.impl.charm.glisten.util.StylesheetTools.replaceStylesheet(StylesheetTools.java:64)
at com.gluonhq.charm.glisten.visual.Theme.assignTo(Theme.java:34)
at com.mysecondapplication.views.PrimaryView.homeScreen(PrimaryView.java:276)
at com.mysecondapplication.views.PrimaryView.lambda$new$0(PrimaryView.java:183)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventdispatcher.dispatchBubblingEvent(CompositeEventdispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventdispatcher.dispatchEvent(BasicEventdispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventdispatchChainImpl.dispatchEvent(EventdispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventdispatcher.dispatchEvent(BasicEventdispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventdispatchChainImpl.dispatchEvent(EventdispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventdispatcher.dispatchEvent(BasicEventdispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventdispatchChainImpl.dispatchEvent(EventdispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventdispatcher.dispatchEvent(BasicEventdispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventdispatchChainImpl.dispatchEvent(EventdispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8889)
at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:208)
at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
at javafx.base/com.sun.javafx.event.CompositeEventHandler$normalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventdispatcher.dispatchBubblingEvent(CompositeEventdispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventdispatcher.dispatchEvent(BasicEventdispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventdispatchChainImpl.dispatchEvent(EventdispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventdispatcher.dispatchEvent(BasicEventdispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventdispatchChainImpl.dispatchEvent(EventdispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventdispatcher.dispatchEvent(BasicEventdispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventdispatchChainImpl.dispatchEvent(EventdispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventdispatcher.dispatchEvent(BasicEventdispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventdispatchChainImpl.dispatchEvent(EventdispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3856)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1851)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2584)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:409)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:299)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:447)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:412)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:446)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:834)
编辑：我做了一些测试，打印出场景既不亮也不暗？我很困惑。
解决方法
暂无找到可以解决该程序问题的有效方法，小编努力寻找整理中！
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