JavaFX FXML 控制器 - 构造函数与初始化方法
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JavaFX FXML controller - constructor vs initialize method
提问by mrbela
My Applicationclass looks like this:
我的Application课是这样的：
public class Test extends Application {
private static Logger logger = LogManager.getRootLogger();
@Override
public void start(Stage primaryStage) throws Exception {
String resourcePath = "/resources/fxml/MainView.fxml";
URL location = getClass().getResource(resourcePath);
FXMLLoader fxmlLoader = new FXMLLoader(location);
Scene scene = new Scene(fxmlLoader.load(), 500, 500);
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
The FXMLLoadercreates an instance of the corresponding controller (given in the FXMLfile via fx:controller) by invoking first the default constructor and then the initializemethod:
在FXMLLoader创建相应的控制器（在所给出的实例FXML经由文件fx:controller通过调用第一默认构造，然后）initialize方法：
public class MainViewController {
public MainViewController() {
System.out.println("first");
}
@FXML
public void initialize() {
System.out.println("second");
}
}
The output is:
输出是：
first
second
So, why does the initializemethod exist? What is the difference between using a constructor or the initializemethod to initialize the controller required things?
那么，为什么该initialize方法存在呢？使用构造函数或initialize方法来初始化控制器所需的东西有什么区别？
Thanks for your suggestions!
感谢您的建议！
采纳答案by Nikos Paraskevopoulos
In a few words: The constructor is called first, then any @FXMLannotated fields are populated, then initialize()is called. So the constructor does NOT have access to @FXMLfields referring to components defined in the .fxml file, while initialize()does have access to them.
简而言之：首先调用构造函数，然后@FXML填充任何带注释的字段，然后initialize()调用。因此，构造函数无权访问@FXML引用 .fxml 文件中定义的组件的字段，但initialize()可以访问它们。
Quoting from the Introduction to FXML:
引自FXML 简介：
[...] the controller can define an initialize() method, which will be called once on an implementing controller when the contents of its associated document have been completely loaded [...] This allows the implementing class to perform any necessary post-processing on the content.
[...] 控制器可以定义一个 initialize() 方法，当相关文档的内容完全加载时，该方法将在实现控制器上调用一次 [...] 这允许实现类执行任何必要的发布- 处理内容。
回答by Itai
The initializemethod is called after all @FXMLannotated members have been injected. Suppose you have a table view you want to populate with data:
在注入initialize所有带@FXML注释的成员后调用该方法。假设您有一个要填充数据的表视图：
class MyController {
@FXML
TableView<MyModel> tableView;
public MyController() {
tableView.getItems().addAll(getDataFromSource()); // results in NullPointerException, as tableView is null at this point.
}
@FXML
public void initialize() {
tableView.getItems().addAll(getDataFromSource()); // Perfectly Ok here, as FXMLLoader already populated all @FXML annotated members.
}
}
回答by gkhaos
In Addition to the above answers, there probably should be noted that there is a legacy way to implement the initialization. There is an interface called Initializablefrom the fxml library.
除了上述答案之外，可能还应该指出，有一种传统的方式来实现初始化。fxml 库中有一个名为Initializable的接口。
import javafx.fxml.Initializable;
class MyController implements Initializable {
@FXML private TableView<MyModel> tableView;
@Override
public void initialize(URL location, ResourceBundle resources) {
tableView.getItems().addAll(getDataFromSource());
}
}
Parameters:
参数：
location - The location used to resolve relative paths for the root object, or null if the location is not known.
resources - The resources used to localize the root object, or null if the root object was not localized.
And the note of the docs why the simple way of using @FXML public void initialize()works:
以及文档说明为什么简单的使用方法@FXML public void initialize()有效：
NOTEThis interface has been superseded by automatic injection of location and resources properties into the controller. FXMLLoader will now automatically call any suitably annotated no-arg initialize() method defined by the controller. It is recommended that the injection approach be used whenever possible.
NOTE此接口已被位置和资源属性自动注入控制器所取代。FXMLLoader 现在将自动调用由控制器定义的任何适当注释的无参数 initialize() 方法。建议尽可能使用注入方法。
