在窗格中按下按钮时出现 JavaFX InvocationTargetException
JavaFX InvocationTargetException when pressing button in Pane
我只是想从我的 JavaFX 项目中的另一个 class 画一条线（作为一些家庭作业的开始）。但是我 运行 正在进入此 InvocationTargetException 以及 NullPointerException 异常。
"C:\Program Files\Java\jdk1.8.0_144\bin\java" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2017.2.4\lib\idea_rt.jar=58260:C:\Program Files\JetBrains\IntelliJ IDEA 2017.2.4\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_144\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\rt.jar;C:\Users\caspe\Desktop\myFinalMiniProject\out\production\myFinalMiniProject" sample.Main
drawing maze..
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
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:8413)
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.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.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$MouseHandler.access00(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:381)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent4(GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null8(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 48 more
Caused by: java.lang.NullPointerException
at sample.KrushkalA.drawMaze(KrushkalA.java:23)
at sample.Controller.doKruskal(Controller.java:13)
... 58 more
我已经尝试了 James_D 中的 this answer，但在尝试了他的解决方案后仍然不会 运行。
主要：
public void start(Stage primaryStage) throws Exception {
Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
primaryStage.setTitle("Hello World");
primaryStage.setScene(new Scene(root, 350, 350));
primaryStage.show();
}
FXML:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.canvas.Canvas?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.layout.Pane?>
<Pane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="350.0"
prefWidth="350.0" xmlns="http://javafx.com/javafx/8.0.121" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
<children>
<Button fx:id="buttonKruskal" layoutX="14.0" layoutY="2.0" mnemonicParsing="false" onAction="#doKruskal"
prefHeight="20.0" prefWidth="100.0" text="Kruskal"/>
<Button fx:id="buttonRecursiveD" layoutX="236.0" layoutY="2.0" mnemonicParsing="false" onAction="#doRecursiveD"
prefHeight="20.0" prefWidth="100.0" text="RecursiveD"/>
<Button fx:id="buttonRecursiveB" layoutX="125.0" layoutY="2.0" mnemonicParsing="false" onAction="#doRecursiveB"
prefHeight="20.0" prefWidth="100.0" text="RecursiveB"/>
<Canvas height="300.0" layoutX="25.0" layoutY="36.0" width="300.0"/>
</children>
</Pane>
控制器：
public void doKruskal(ActionEvent event) {
System.out.println("drawing maze..");
KrushkalA kruAlg = new KrushkalA();
kruAlg.drawMaze();
// kruAlg.solveMaze();
}
KrushkalA class:
@FXML
Canvas canvas;
GraphicsContext gc;
public void drawMaze(){
gc = canvas.getGraphicsContext2D();
gc.strokeLine(0,0,300,50);
}
也许这就是我想要做的； 运行 来自控制器的 KrushkalA class 中的一个方法，它在按下按钮时在 canvas 中绘制一条线或只是做一些事情。
这是错误的做法吗？我可以 运行 在我的控制器 class 中导致异常的代码，但不能来自任何其他 class？示例代码将不胜感激。
您的代码不起作用的原因是您希望 canvas 从 FXML 注入到您的 KrushkalA 实例中。这根本不是它的工作原理：@FXML-注入是在加载 FXML 文件时由 FXMLLoader 完成的，并且控制器中任何 @FXML-注释字段 instance 使用 FXML 文件中匹配 fx:id 的相应元素进行初始化。即使您将 fx:id 属性添加到 FXML 中定义的 canvas，FXMLLoader 也无法知道 KrushkalA 对象（甚至不是那个时候创建的，虽然如果是的话也无济于事）。
无论如何，这里的整个前提似乎都有缺陷。允许对 UI 元素的引用从控制器中转义通常不是一个好主意。假设在未来的某个时候，您决定不再使用 Canvas 来绘制它（例如，您可能决定将 Line 或其他节点添加到 Pane).在这种情况下，您真的只需要修改 FXML 和控制器 class；如果您允许 KrushkalA class 访问 canvas，那么您也需要更改它，并且您需要查看 class 是否通过了canvas 提及其他任何人。如果以这种方式破坏封装，维护它会变得更加困难。
如果你的 KrushkalA class 真的只是在实现算法，它应该与 UI 没有任何关系。我认为您正在创建一个迷宫（或者，更抽象地说，一个图形的生成树），因此您的 drawMaze() 方法应该只计算迷宫和 return 结果。在它的核心，迷宫只是单元格（节点）之间的边界（或边）的集合，所以我想我会定义一个 Boundary class 并用一些简单的表示它是哪个边界（也许int x、int y 和 boolean horizontal 字段，或其他方便的字段）；那么你将有：
public class KrushkalA {
public List<Boundary> drawMaze() {
List<Boundary> maze = new ArrayList<>();
// implementation of algorithm...
return maze ;
}
}
然后回到你的控制器，你会做：
public class MazeController {
@FXML
private Canvas canvas ;
@FXML
private void doKrushkal(ActionEvent e) {
KrushkalA kruAlg = new KrushkalA();
List<Boundary> maze = kruAlg.drawMaze();
// now render maze on canvas, using data in the List<Boundary> from above
renderMaze(maze);
}
private void renderMaze(List<Boundary> maze) {
// clear canvas, iterate through boundaries in maze,
// and draw lines in appropriate place, etc.
}
}
当然，还要将 fx:id="canvas" 添加到 FXML 中的 <Canvas> 元素。
这种方法妥善地管理了关注点分离并遵守单一职责原则：控制器只负责更新 UI，并不关心算法是如何实现的，KrushkalA class 只负责实现算法，并不关心 UI 是如何呈现的（或者即使有 是 一个 UI...).
如果你真的想要算法 class 在 canvas 上渲染迷宫，我 强烈不推荐， 那么你当然可以只需将 canvas 传递给它：
@FXML
private void doKrushkal(ActionEvent e) {
KrushkalA kruAlg = new KrushkalA();
kruAlg.drawMaze(canvas);
}
和
public class KrushkalA {
public void drawMaze(Canvas canvas) {
// compute maze AND render it on canvas...
}
}
我只是想从我的 JavaFX 项目中的另一个 class 画一条线（作为一些家庭作业的开始）。但是我 运行 正在进入此 InvocationTargetException 以及 NullPointerException 异常。
"C:\Program Files\Java\jdk1.8.0_144\bin\java" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2017.2.4\lib\idea_rt.jar=58260:C:\Program Files\JetBrains\IntelliJ IDEA 2017.2.4\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_144\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_144\jre\lib\rt.jar;C:\Users\caspe\Desktop\myFinalMiniProject\out\production\myFinalMiniProject" sample.Main
drawing maze..
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8413)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$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.access00(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:381)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent4(GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
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$null8(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 48 more
Caused by: java.lang.NullPointerException
at sample.KrushkalA.drawMaze(KrushkalA.java:23)
at sample.Controller.doKruskal(Controller.java:13)
... 58 more
我已经尝试了 James_D 中的 this answer，但在尝试了他的解决方案后仍然不会 运行。
主要：
public void start(Stage primaryStage) throws Exception {
Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
primaryStage.setTitle("Hello World");
primaryStage.setScene(new Scene(root, 350, 350));
primaryStage.show();
}
FXML:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.canvas.Canvas?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.layout.Pane?>
<Pane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="350.0"
prefWidth="350.0" xmlns="http://javafx.com/javafx/8.0.121" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
<children>
<Button fx:id="buttonKruskal" layoutX="14.0" layoutY="2.0" mnemonicParsing="false" onAction="#doKruskal"
prefHeight="20.0" prefWidth="100.0" text="Kruskal"/>
<Button fx:id="buttonRecursiveD" layoutX="236.0" layoutY="2.0" mnemonicParsing="false" onAction="#doRecursiveD"
prefHeight="20.0" prefWidth="100.0" text="RecursiveD"/>
<Button fx:id="buttonRecursiveB" layoutX="125.0" layoutY="2.0" mnemonicParsing="false" onAction="#doRecursiveB"
prefHeight="20.0" prefWidth="100.0" text="RecursiveB"/>
<Canvas height="300.0" layoutX="25.0" layoutY="36.0" width="300.0"/>
</children>
</Pane>
控制器：
public void doKruskal(ActionEvent event) {
System.out.println("drawing maze..");
KrushkalA kruAlg = new KrushkalA();
kruAlg.drawMaze();
// kruAlg.solveMaze();
}
KrushkalA class:
@FXML
Canvas canvas;
GraphicsContext gc;
public void drawMaze(){
gc = canvas.getGraphicsContext2D();
gc.strokeLine(0,0,300,50);
}
也许这就是我想要做的； 运行 来自控制器的 KrushkalA class 中的一个方法，它在按下按钮时在 canvas 中绘制一条线或只是做一些事情。
这是错误的做法吗？我可以 运行 在我的控制器 class 中导致异常的代码，但不能来自任何其他 class？示例代码将不胜感激。
您的代码不起作用的原因是您希望 canvas 从 FXML 注入到您的 KrushkalA 实例中。这根本不是它的工作原理：@FXML-注入是在加载 FXML 文件时由 FXMLLoader 完成的，并且控制器中任何 @FXML-注释字段 instance 使用 FXML 文件中匹配 fx:id 的相应元素进行初始化。即使您将 fx:id 属性添加到 FXML 中定义的 canvas，FXMLLoader 也无法知道 KrushkalA 对象（甚至不是那个时候创建的，虽然如果是的话也无济于事）。
无论如何，这里的整个前提似乎都有缺陷。允许对 UI 元素的引用从控制器中转义通常不是一个好主意。假设在未来的某个时候，您决定不再使用 Canvas 来绘制它（例如，您可能决定将 Line 或其他节点添加到 Pane).在这种情况下，您真的只需要修改 FXML 和控制器 class；如果您允许 KrushkalA class 访问 canvas，那么您也需要更改它，并且您需要查看 class 是否通过了canvas 提及其他任何人。如果以这种方式破坏封装，维护它会变得更加困难。
如果你的 KrushkalA class 真的只是在实现算法，它应该与 UI 没有任何关系。我认为您正在创建一个迷宫（或者，更抽象地说，一个图形的生成树），因此您的 drawMaze() 方法应该只计算迷宫和 return 结果。在它的核心，迷宫只是单元格（节点）之间的边界（或边）的集合，所以我想我会定义一个 Boundary class 并用一些简单的表示它是哪个边界（也许int x、int y 和 boolean horizontal 字段，或其他方便的字段）；那么你将有：
public class KrushkalA {
public List<Boundary> drawMaze() {
List<Boundary> maze = new ArrayList<>();
// implementation of algorithm...
return maze ;
}
}
然后回到你的控制器，你会做：
public class MazeController {
@FXML
private Canvas canvas ;
@FXML
private void doKrushkal(ActionEvent e) {
KrushkalA kruAlg = new KrushkalA();
List<Boundary> maze = kruAlg.drawMaze();
// now render maze on canvas, using data in the List<Boundary> from above
renderMaze(maze);
}
private void renderMaze(List<Boundary> maze) {
// clear canvas, iterate through boundaries in maze,
// and draw lines in appropriate place, etc.
}
}
当然，还要将 fx:id="canvas" 添加到 FXML 中的 <Canvas> 元素。
这种方法妥善地管理了关注点分离并遵守单一职责原则：控制器只负责更新 UI，并不关心算法是如何实现的，KrushkalA class 只负责实现算法，并不关心 UI 是如何呈现的（或者即使有 是 一个 UI...).
如果你真的想要算法 class 在 canvas 上渲染迷宫，我 强烈不推荐， 那么你当然可以只需将 canvas 传递给它：
@FXML
private void doKrushkal(ActionEvent e) {
KrushkalA kruAlg = new KrushkalA();
kruAlg.drawMaze(canvas);
}
和
public class KrushkalA {
public void drawMaze(Canvas canvas) {
// compute maze AND render it on canvas...
}
}