java - 尝试使用 javafx 将项目分配给选择框时出现 InspirationTargetException

Question

向我的选择框添加选项的简单尝试会导致 InitationTargetException。我真的不明白抛出这个异常的原因，所以解释和解决方案会很棒!这是我在 FXMLDocumentController 类中的代码:

public class FXMLDocumentController implements Initializable {

    @FXML
    private ChoiceBox<?> pilot;

    public FXMLDocumentController(){  

         setMembersList();
    }


    private void setMembersList(){
        List<String> list = new ArrayList<String>();
        list.add("Item A");
        list.add("Item B");
        list.add("Item C");
        ObservableList obList = FXCollections.observableList(list);
        pilot.setItems(obList);
    }
}

这是我得到的...:

Exception in Application start method

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:483)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:367)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:305)
    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:483)
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:894)
    at com.sun.javafx.application.LauncherImpl.access$000(LauncherImpl.java:56)
    at com.sun.javafx.application.LauncherImpl$1.run(LauncherImpl.java:158)
    at java.lang.Thread.run(Thread.java:745)

使用试验和错误，异常肯定会在 pilot.setItems(obList); 行中抛出，因为当我摆脱此行时，它会启动而没有任何异常。

Answer 1

您的 FXML 注入(inject)的 ChoiceBox 在调用构造函数时不会被初始化，因此您将得到一个 NullPointerException (pilot 为 null)。

相反，从 initialize() 方法调用您的代码。我还会正确输入您的 ChoiceBox 和 ObservableList:

public class FXMLDocumentController {

    @FXML
    private ChoiceBox<String> pilot;

    public void initialize(){  

         setMembersList();
    }


    private void setMembersList(){
        List<String> list = new ArrayList<String>();
        list.add("Item A");
        list.add("Item B");
        list.add("Item C");
        ObservableList<String> obList = FXCollections.observableList(list);
        pilot.setItems(obList);
    }
}