*我是 java/编程新手。
我编写了以下代码示例来尝试找出我的问题,然后给出我的问题的清晰示例。我想让我的程序根据它们在应用程序中的功能分为不同的类: 主要的 MainController - 驱动 JavaFX GUI。 初始化程序 - 输入数据的语义验证。 模型 - 对数据执行计算并将结果发送回 MainController。
我被卡住的地方是初始化程序,特别是 linkedhashmap 和第一次验证检查,抛出一个 nullpointerexception。如果所有内容都在一个类中,则不会发生这种情况(我从一个类中的所有内容开始,现在正在学习如何在单独的类中构建结构,等等)。如果我不使用任何 JavaFX 功能,它也不会发生。
例如,这个有效:
package helloWorld;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello world!");
HashmapExample hashy = new HashmapExample();
System.out.println(hashy.initialiser());
}
}
package helloWorld;
import java.util.LinkedHashMap;
import java.util.Map;
public class HashmapExample {
private Map<String,String> testMap = new LinkedHashMap<>();
public void mapper() {
testMap.put("one","a");
testMap.put("two","b");
testMap.put("three","c");
}
public String initialiser() {
mapper();
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
String message;
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
但这不是:
package helloWorldFX;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
public class Main extends Application {
@Override
public void start(Stage primaryStage) {
try {
VBox root = (VBox)FXMLLoader.load(getClass().getResource("MainGUI.fxml"));
Scene scene = new Scene(root,400,400);
scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
primaryStage.setScene(scene);
primaryStage.show();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
}
package helloWorldFX;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.TextArea;
public class MainController {
@FXML private TextArea outputMessage;
public void run(ActionEvent event) {
Initialiser initialiser = new Initialiser();
outputMessage.setText(initialiser.checker());
}
}
package helloWorldFX;
import java.util.LinkedHashMap;
import java.util.Map;
import javafx.fxml.FXML;
import javafx.scene.control.TextField;
public class Initialiser {
@FXML private TextField one;
@FXML private TextField two;
@FXML private TextField three;
private Map<TextField,String> testMap = new LinkedHashMap<>();
public void mapper() {
testMap.put(one,"a");
testMap.put(two,"b");
testMap.put(three,"c");
}
public String checker() {
mapper();
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().getText().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
String message;
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
当我在 eclipse 中进行覆盖运行时,我可以看出它可能是由行引起的
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null) ;
但我不完全确定。
我刚刚在场景生成器中注意到字段“一”、“二”和“三”没有显示为文本字段的有效 ID,因为它们不在 MainController 类中。这一定与问题有关,但我不知道如何解决。
FXML 文件,按要求:请记住,它是一组示例代码,并非真正的程序,因此布局毫无意义。
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.TextArea?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.VBox?>
<VBox prefHeight="300.0" prefWidth="300.0" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="helloWorldFX.MainController">
<children>
<TextField />
<TextField />
<TextField />
<Button mnemonicParsing="false" onAction="#run" text="Button" />
<TextArea fx:id="outputMessage" prefHeight="200.0" prefWidth="200.0" />
</children>
</VBox>
错误信息:
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1787)
at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
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.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:8890)
at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:206)
at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3862)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2590)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:409)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:299)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:447)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:411)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:446)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1782)
... 46 more
Caused by: java.lang.NullPointerException
at helloWorldFX.Initialiser.lambda$0(Initialiser.java:29)
at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:176)
at java.base/java.util.Spliterators$IteratorSpliterator.tryAdvance(Spliterators.java:1812)
at java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:127)
at java.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:502)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:488)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:150)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:543)
at helloWorldFX.Initialiser.checker(Initialiser.java:29)
at helloWorldFX.MainController.run(MainController.java:15)
... 58 more
最佳答案
解决方法:
因此,根据评论和对可能原因的更多思考,我想出了这个解决方法。
我在 MainController 中实例化并填充 Map
,然后实例化 Initialiser 类,该类现在通过构造函数将 Map
作为参数。然后我从 Initialiser 对象调用 checker 方法,它对实例化时发送到对象的数据运行语义检查。
据我所知,问题在于一个 fxml 文件只能处理一个 Controller 类,因此除了主 Controller 类之外,您无法使用 TextFields
填充 map 。如果这样做,getText
方法将抛出 nullpointerexception
,因为它指向的 TextFields
在技术上不存在于 fxml 中。
查看修改后的代码:
package helloWorldFX;
import java.util.LinkedHashMap;
import java.util.Map;
import javafx.fxml.FXML;
import javafx.scene.control.TextField;
import javafx.scene.control.TextArea;
import javafx.event.ActionEvent;
public class MainController {
@FXML private TextField one;
@FXML private TextField two;
@FXML private TextField three;
@FXML private TextArea outputMessage;
public void run(ActionEvent event) {
Map<TextField, String> testMap = new LinkedHashMap<>();
testMap.put(one,"a");
testMap.put(two,"b");
testMap.put(three,"c");
Initialiser initialiser = new Initialiser(testMap);
outputMessage.setText(initialiser.checker());
}
}
package helloWorldFX;
import java.util.Map;
import javafx.scene.control.TextField;
public class Initialiser {
private Map<TextField, String> values;
public Initialiser(Map<TextField, String> mappedValues) {
this.values = mappedValues;
}
String message;
public String checker() {
String errorField = values.entrySet().stream().filter(entry -> entry.getKey().getText().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
在这一点上,由于我缺乏经验,我不知道这实际上是一种变通方法还是真正正确的方法 - 也许有人可以帮助填补这一部分。
关于java - 为什么我不能通过从另一个类调用方法来使用 JavaFX 文本字段生成 map ?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58333762/