java - 调用 Controller 方法时出现 InspirationTargetException - JavaFX

Question

当我尝试从 Controller (JavaFX)调用方法时，我收到一个 InvocableTargetException 异常，代码如下:

    public void start(Stage stage) throws Exception {

    URL location = getClass().getResource("startScreen.fxml");
    FXMLLoader loader = new FXMLLoader();

    loader.setLocation(location);
    loader.setBuilderFactory(new JavaFXBuilderFactory());

    //Getting hte controller
    StartScreenController s = (StartScreenController)loader.getController();

    //Where error occurs
    s.setParent(this);

    Parent root = (Parent) loader.load(location.openStream());

    Scene scene = new Scene(root);
    stage.setScene(scene);
    stage.show();
}

当我删除“setParent”行时，它工作正常。

这似乎对其他人有效(就我自己尝试解决此问题时所看到的而言)。

如有任何帮助，我们将不胜感激，谢谢。

我得到的错误(s.setParent 是第 38 行)

    Exception in Application start method
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.javafx.main.Main.launchApp(Main.java:642)
    at com.javafx.main.Main.main(Main.java:805)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:403)
    at com.sun.javafx.application.LauncherImpl.access$000(LauncherImpl.java:47)
    at com.sun.javafx.application.LauncherImpl$1.run(LauncherImpl.java:115)
    at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.NullPointerException
    at johnsoft.dndcommunication.DndCommunication.start(DndCommunication.java:38)
    at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:319)
    at com.sun.javafx.application.PlatformImpl$5.run(PlatformImpl.java:206)
    at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:173)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29)
    at com.sun.glass.ui.win.WinApplication$3$1.run(WinApplication.java:73)
    ... 1 more
Java Result: 1

Answer 1

我猜，
您正尝试在加载 FXML 文件之前访问 Controller 类。

StartScreenController s = (StartScreenController)loader.getController();

// so StartScreenController s is null here thus NPE
s.setParent(this);

// here loading is happening after getting the controller class, which is wrong. 
// Get the controller after loading is completed.

Parent root = (Parent) loader.load(location.openStream());