在2个控制器之间传递值时出现空指针异常

Question

但是最后一个选项也没有帮助，因为我仍然总是得到相同的错误：空指针异常。它来自模型生成密码的行，所获得的字符串绑定到seconde视图的控制器中的一个值。

我有点困在这里，我想混合两种不同的方法来编码我的视图不是最好的方法。尽管如此，也许我没有正确地进行绑定，这是我最想和最希望的。

因此，我的第一个视图的控制器如下所示（生成密码）：

public class GeneratePasswordController implements EventHandler<MouseEvent>{

  @FXML private displayPasswordController displayPasswordController;

  @Override
  public void handle(MouseEvent event) {
    //Doing some stuff that works, then generating the password and null pointer exception occurs here
    //The method getNewPassword() returns a String (the password).
    //The model is accessed statically (an instance has been created in the Application file (Main.java)).
    displayPasswordController.pwdValueProperty().bind(Bindings.createStringBinding(()
                                          -> Main.myModel.getNewPassword()));
  }
}

public class NewPswdController {
  @FXML private TextField displayPassword;

  private final StringProperty pwdValue = new SimpleStringProperty("Password");

  public StringProperty pwdValueProperty() {
    return pwdValue;
  }

  public String getPwdValue() {
    return pwdValue.get();
  }

  public void setPwdValue(String value) {
    this.pwdValue.set(value);
  }

  @FXML
  void initialize() {
    dispPassword.textProperty().bind(Bindings.format("%s", pwdValue));
  }
}

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at s03.GeneratePasswordController.handle(GeneratePasswordController.java:61)
at s03.GeneratePasswordController.handle(GeneratePasswordController.java:1)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at javafx.event.Event.fireEvent(Unknown Source)
at javafx.scene.Scene$MouseHandler.process(Unknown Source)
at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source)
at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$350(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$$Lambda$271/1952832519.get(Unknown Source)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
at com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
at com.sun.glass.ui.View.notifyMouse(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$145(Unknown Source)
at com.sun.glass.ui.win.WinApplication$$Lambda$36/1232367853.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

Answer 1

故障来自显示密码的控制器。null指针很可能来自这样一个事实，即没有该控制器的实例。

错误的地方在于我包含了使用@fxml注释显示密码的控制器。

在生成密码的控制器中，下面的代码可以正常工作：

try {
  //Load the view and controller
  FXMLLoader loader = new FXMLLoader(getClass().getResource("displayPassword.fxml"));
  Parent displayPassword = (Parent)loader.load();
  Scene displayPasswordScene = new Scene(displayPassword);
  displayPasswordController controller = loader.getController();
  //Generate the password and set it
  controller.setPwdValue(Pastis.model.getNewPassword());
  //Load the new view on the stage
  Main.getStage().setScene(displayPasswordScene);
  Main.getStage().show();      
} catch (IOException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
}