尝试从文本字段获取文本时出现 NPE？

Question

所以我的计划是从文本字段中获取文本，将其保存在“currentvalue”变量中，并在每次从按钮调用其中一种方法时保存一个新值。这是我的控制器 Class:

package application;



import java.io.IOException;

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TextField;
import javafx.stage.Stage;


public class Controller {
@FXML
Button buttonyes,buttonno;
private Stage stage;
private Scene scene;
private Parent root;

public void yes(ActionEvent event) throws IOException {
 root = FXMLLoader.load(getClass().getResource("Order.fxml"));
 stage = (Stage)((Node)event.getSource()).getScene().getWindow();
 scene = new Scene(root);
 stage.setScene(scene);
 stage.show();
}
 
 public void no(ActionEvent event) {
  System.exit(0);
 }
 
@FXML
Button buttonback;

public void back(ActionEvent event) throws IOException{
    root = FXMLLoader.load(getClass().getResource("Welcome.fxml"));
     stage = (Stage)((Node)event.getSource()).getScene().getWindow();
     scene = new Scene(root);
     stage.setScene(scene);
     stage.show();
}

@FXML
private TextField display = new TextField("0,00"); // I either get a NFE here 


double currentvalue = Double.parseDouble(display.getText()); //or a NPE here if I delete the new TextField line
double value1 = 3.00;
double value2 = 2.50;
double value3 = 2.00;
double value4 = 1.50;
double value5 = 1.00;

public void order3() {
    display.setText(String.valueOf(currentvalue+value1));
}

public void order25() {
    display.setText(String.valueOf(currentvalue+value2));
}

public void order2() {
    display.setText(String.valueOf(currentvalue+value3));
}

public void order15() {
    display.setText(String.valueOf(currentvalue+value4));
}
public void order1() {
    display.setText(String.valueOf(currentvalue+value5));
}

public void order(ActionEvent event) throws IOException{
    root = FXMLLoader.load(getClass().getResource("Bye.fxml"));
     stage = (Stage)((Node)event.getSource()).getScene().getWindow();
     scene = new Scene(root);
     stage.setScene(scene);
     stage.show();
}

}

所以基本上我是在尝试计算一个新值，以便在按下按钮后显示在文本字段中。我已经尝试了很多我在网上找到的解决方案，但似乎没有任何效果，这就是我在这里问的原因。

这是 NFE 的错误

javafx.fxml.LoadException: 
/C:/Users/daydr/eclipse-workspace/Projektarbeit-Bestellen/Bestellservice/bin/application/Welcome.fxml:11

    at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3323)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3280)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3249)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3222)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3199)
    at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3192)
    at application.Main.start(Main.java:14)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:846)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:474)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:447)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:446)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:174)
    at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: java.lang.NumberFormatException: For input string: "0,00"
    at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2054)
    at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
    at java.base/java.lang.Double.parseDouble(Double.java:549)
    at application.Controller.<init>(Controller.java:52)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:64)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
    at java.base/java.lang.reflect.ReflectAccess.newInstance(ReflectAccess.java:128)
    at java.base/jdk.internal.reflect.ReflectionFactory.newInstance(ReflectionFactory.java:350)
    at java.base/java.lang.Class.newInstance(Class.java:645)
    at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processAttribute(FXMLLoader.java:938)
    at javafx.fxml/javafx.fxml.FXMLLoader$InstanceDeclarationElement.processAttribute(FXMLLoader.java:982)
    at javafx.fxml/javafx.fxml.FXMLLoader$Element.processStartElement(FXMLLoader.java:229)
    at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processStartElement(FXMLLoader.java:754)
    at javafx.fxml/javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2808)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2634)
    ... 17 more

和 NPE 的那个

javafx.fxml.LoadException: 
/C:/Users/daydr/eclipse-workspace/Projektarbeit-Bestellen/Bestellservice/bin/application/Welcome.fxml:11

    at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3323)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3280)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3249)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3222)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3199)
    at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3192)
    at application.Main.start(Main.java:14)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:846)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:474)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:447)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:446)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:174)
    at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.control.TextField.getText()" because "this.display" is null
    at application.Controller.<init>(Controller.java:52)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:64)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
    at java.base/java.lang.reflect.ReflectAccess.newInstance(ReflectAccess.java:128)
    at java.base/jdk.internal.reflect.ReflectionFactory.newInstance(ReflectionFactory.java:350)
    at java.base/java.lang.Class.newInstance(Class.java:645)
    at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processAttribute(FXMLLoader.java:938)
    at javafx.fxml/javafx.fxml.FXMLLoader$InstanceDeclarationElement.processAttribute(FXMLLoader.java:982)
    at javafx.fxml/javafx.fxml.FXMLLoader$Element.processStartElement(FXMLLoader.java:229)
    at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processStartElement(FXMLLoader.java:754)
    at javafx.fxml/javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2808)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2634)
    ... 17 more

Answer 1

由于您没有包含 FXML，我们只能假设 TextField“显示”在 FXML 文件中。这意味着它将通过 FXML 加载器创建。 不要将 display 分配给新的 TextField。

您可以在初始化方法中访问显示。

@Override
public void initialize(){
    currentValue = Double.parseDouble(display.getText());
}

您的区域设置有问题，因此您可以使用本地化解析来计算文本。

currentValue = NumberFormat.getInstance().parse(display.getText()).doubleValue();

这将使用默认语言环境，可能更可能不使用逗号。

最后，您可能要考虑绑定。由于您使用的是 javafx.

DoubleProperty currentValueProperty = new DoubleProperty();
public void initialize(){
    display.textProperty().bindBidirectional( currentValueProperty, NumberFormat.getInstance() )
}

尝试从文本字段获取文本时出现 NPE？

NPE when trying to get text from a textfield?

java

javafx

scenebuilder