每个声明都需要@FXML吗？ [英] Is @FXML needed for every declaration?

问题描述

每个声明都需要@FXML，还是第一个？

Is @FXML needed for every declaration or just for the first?

换句话说，我应该使用

@FXML
public Label timerLabel = new Label();
@FXML
public TextField mainTextField, projectTextField ;
@FXML
public Button goButton, deleteAllButton ;
@FXML
public ComboBox<String> projectComboBox ;
@FXML
public TableView<Entry> mainTable ;
@FXML
public TableColumn<Entry, String> titleColumn, timeColumn, dateColumn ;
@FXML
public TableColumn<Entry, Boolean> checkColumn, buttonColumn ;
@FXML
public checkBox checkAllCheckBox ;

或

@FXML
public Label timerLabel = new Label();
public TextField mainTextField, projectTextField ;
public Button goButton, deleteAllButton ;
public ComboBox<String> projectComboBox ;
public TableView<Entry> mainTable ;
public TableColumn<Entry, String> titleColumn, timeColumn, dateColumn ;
public TableColumn<Entry, Boolean> checkColumn, buttonColumn ;
public checkBox checkAllCheckBox ;

谢谢！

推荐答案

@FXML 注释启用 FXMLLoader 将FXML文件中定义的值注入引用在控制器类中。换句话说，如果您使用 @FXML 注释 timerLabel ，那么它将由<$ c $初始化c> FXMLLoader 当FXML文件中的元素使用 fx：id =调用 load（）方法时timerLabel。正如其他人在评论中指出的那样，这意味着你永远不应该写代码

The @FXML annotation enables an FXMLLoader to inject values defined in an FXML file into references in the controller class. In other words, if you annotate your timerLabel with @FXML, then it will be initialized by the FXMLLoader when the load() method is called by an element in the FXML file with fx:id="timerLabel". As others have pointed out in the comments, this means you should never write code like

@FXML
private Label timerLabel = new Label();

此处 timerLabel 将首先初始化为您在代码中创建的 new Label（）; ，然后几乎立即重新初始化为FXML文件中定义的值。这至多是多余的，最糟糕的是误导。如果您没有将变量名称正确匹配到 fx：id ，则您的变量将引用错误的标签并且错误将很难追踪。

Here timerLabel will first be initialized to the new Label(); you create in the code, and will then almost immediately be re-initialized to the value defined in the FXML file. This is at best redundant, and at worst misleading. If you don't correctly match the variable names to the fx:id, your variable will be referring to the wrong Label and the error will be very difficult to track down.

要找到您的实际问题：

何时 FXMLLoader 加载FXML文件，它会尝试将任何具有 fx：id 属性的元素注入控制器。它将查找

When the FXMLLoader loads the FXML file, it will attempt to inject any elements that have an fx:id attribute into the controller. It will look for

1. 任何 public 字段，其变量名称与<$匹配c $ c> fx：id 属性，或


2. 任何字段（ public 或不具有与 fx：id 属性匹配的变量名称，该属性使用 @FXML 进行注释。

1. Any public field with a variable name matching the fx:id attribute, or
2. Any field (public or not) with a variable name matching the fx:id attribute that is annotated with @FXML.

因此在您的示例中，由于您的所有字段都是 public ，因此您可以省略所有字段 @FXML 注释（即使是第一个）也会有效。

So in your example, since all your fields are public, you can omit all the @FXML annotations (even the first) and it will still work.

但是，如果你遵循良好做法并使你的字段 private ，然后每个声明必须注释 @FXML 才能使注入工作。

However, if you follow good practice and make your fields private, then each declaration must be annotated @FXML for the injection to work.

所以

@FXML
private Label timerLabel;
@FXML
private TextField mainTextField;

等可行，但

@FXML
private Label timerLabel;
private TextField mainTextField;

不会。

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