我试图访问加载fxml的窗口的控制器类的实例。它加载没有错误,但是当我尝试打印使用的帐户数时fxmlLoader.getController()导致空指针异常?
System.out.println("from NAW: "+ NAC.newAccModel.users.getNumAccs());
它在下面给出空指针例外。 (第36行是println
)
java.lang.NullPointerException
at muselogin.newAccountWindow.<init>(newAccountWindow.java:36)
at muselogin.MuseLoginController.initialize(MuseLoginController.java:84)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3214)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
at muselogin.MuseLogin.start(MuseLogin.java:22)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
这里就是我想打电话给getController()
public class newAccountWindow extends Application {
Stage stage = new Stage();
newAccountController NAC = new newAccountController();
public newAccountWindow(){
Parent root=null;
try{
FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("newAccountWindow.fxml"));
root = fxmlLoader.load(getClass().getResource("newAccountWindow.fxml"));
// fxmlLoader.setBuilderFactory(new JavaFXBuilderFactory());
NAC = (newAccountController) fxmlLoader.getController();
System.out.println("from NAW: "+NAC.newAccModel.users.getNumAccs());
}catch(Exception e){
e.printStackTrace();
}
Scene scene = new Scene(root);
//scene.getStylesheets().add(MuseLogin.class.getResource("newAccCSS.css").toExternalForm());
stage.setScene(scene);
}
这里控制器,如果它的事项
public class newAccountController implements Initializable {
newAccountModel newAccModel;
@FXML
private TextField usernameField;
@FXML
private PasswordField passwordField;
@FXML
private Button createAccount;
@FXML
private PasswordField confirmField;
@FXML
private Label usernameBlankMessage;
@FXML
private Label usernameTakenMessage;
@FXML
private Label passwordMessage;
//counter to check if all 3 conditions are met
int makeAcc = 0;
//action event for make account button clicked
@FXML
private void createAccountClicked(ActionEvent event) {
//does account creation stuff
}
public int getNumAccs(){
return newAccModel.users.getNumAccs();
}
//required initialize function, initializes model
@Override
public void initialize(URL url, ResourceBundle rb) {
newAccModel = new newAccountModel();
}
}
'newAccountModel()'的构造函数有什么作用?您不提供代码。它是否将用户与'newAccountModel'相关联,并将参考存储在'newAccountModel'的'users'成员中?如果不是,那可能是你的NullPointerException的源头:'users'为null,所以'users.getItems()'抛出一个NullPointerException异常。请参阅:[什么是空指针异常,以及如何解决它?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i -fix-it)请遵循[class命名约定](http://www.iwombat.com/standards/JavaStyleGuide.html)。 – jewelsea