当应用程序关闭时尝试获取 mainApp 中文本字段的文本时出现 java.lang.NullPointerException

Question

I am new to javaFX and i am trying to get the value of a text field when my application is closing so i used

FXMLLoader loader = new FXMLLoader(getClass().getResource("/fxml/Scene.fxml"));
FXMLController controllerClass = loader.getController();
loader.load();
controllerClass.getTextFieldValue();
System.out.println("closing");

inside

stage.setOnCloseRequest()

but i always get a java.lang.NullPointerException.

this is getTextfieldValue()

System.out.println(textField.getText());

so basically this is what I want to achieve, I want to get the value in a text field when the my application is closing. so I have my stage.onCloseRequest() method in my mainApp class but the textField.getText() is always returning an empty string. And I want it to return the current text in the textField.

Answer 1

You must run load() before you get the controller.

Try this code:

FXMLLoader loader = new FXMLLoader(getClass().getResource("/fxml/Scene.fxml"));
loader.load();
FXMLController controllerClass = loader.getController();
controllerClass.getTextFieldValue();
System.out.println("closing");

Answer 2

Did you forget to add fx:id in your Scene.fxml ? Please, provide more example of your code. I don't know what's happening in your FXML file. I think there may be some kind of xml code missing.

Although I don't know what you are trying to achieve, but I think there is easier and correct way to do it.

FXMLLoader loader = new FXMLLoader(getClass().getResource("/fxml/Scene.fxml")));
loader.setController(new FXMLController()); // you can not get controller, unless you set it first
FXMLController controllerClass = loader.getController();
controllerClass.getTextFieldValue();

This always be null if you do not set value to getTextFieldValue before

Answer 3

• To remove the NullPointerException first run load() before you get the controller.
• To get the value of the textfield when closing the application, I used the Preferences class from java.util.prefs to save the content of the textfield, then I overrode the stop() method in my mainApp and got back the saved value in it.

---

Not sure this is the best way to do it but it worked for me, Thanks for all the help.