IntelliJ IDE中JavaFX Controller无法检测识别FXML绑定对象问题

项目背景 #

首次使用JavaFX开发计算器项目，同步尝试编写CSS样式，参考基础教程完成代码后，在Controller层遇到对象无法识别的问题。

相关代码 #

Main类代码 #

package app;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("mainFX.fxml"));
        Scene sceneMain = new Scene(root);
        primaryStage.setScene(sceneMain);       //scene setup

        String css = this.getClass().getResource("calcFX.css").toExternalForm();
        sceneMain.getStylesheets().add(css);    //adding css

        primaryStage.setResizable(false);
        primaryStage.setTitle("CalcFX");
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

Controller类代码 #

package app;

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import javafx.scene.text.Text;

public class Controller {

    private Text text = new Text("");
    @FXML
    private Label display;
    display.setText(text);
}

FXML文件代码 #

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.RowConstraints?>

<AnchorPane id="pane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="450.0" prefWidth="350.0" xmlns="http://javafx.com/javafx/16" xmlns:fx="http://javafx.com/fxml/1" fx:controller="app.Controller">
   <children>
      <Label id="display" layoutX="25.0" layoutY="15.0" prefHeight="200.0" prefWidth="300.0" text="" />

      <GridPane hgap="6.0" layoutX="25.0" layoutY="225.0" prefHeight="200.0" prefWidth="300.0" vgap="6.0">
        <columnConstraints>
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="45.0" />
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="45.0" />
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="45.0" />
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="45.0" />
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="45.0" />
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="45.0" />
        </columnConstraints>
        <rowConstraints>
          <RowConstraints minHeight="10.0" prefHeight="45.0" vgrow="SOMETIMES" />
          <RowConstraints minHeight="10.0" prefHeight="45.0" vgrow="SOMETIMES" />
          <RowConstraints minHeight="10.0" prefHeight="45.0" vgrow="SOMETIMES" />
          <RowConstraints minHeight="10.0" prefHeight="45.0" vgrow="SOMETIMES" />
        </rowConstraints>
         <children>
            <Button id="b0" mnemonicParsing="false" onAction="#Press0" prefHeight="45.0" prefWidth="45.0" stylesheets="@calcFX.css" text="0" GridPane.columnIndex="1" GridPane.rowIndex="3" />
            <Button id="b1" mnemonicParsing="false" onAction="#Press1" prefHeight="45.0" prefWidth="45.0" stylesheets="@calcFX.css" text="1" GridPane.rowIndex="2" />
            <Button id="b2" mnemonicParsing="false" onAction="#Press2" prefHeight="45.0" prefWidth="45.0" stylesheets="@calcFX.css" text="2" GridPane.columnIndex="1" GridPane.rowIndex="2" />
            <Button id="b3" mnemonicParsing="false" onAction="#Press3" prefHeight="45.0" prefWidth="45.0" stylesheets="@calcFX.css" text="3" GridPane.columnIndex="2" GridPane.rowIndex="2" />
         </children>
      </GridPane>
   </children>
</AnchorPane>

问题描述 #

尝试引用Label类型的display对象时，IDE提示该对象未定义，Text类型的text元素也无法被IDE正确识别为Text对象。

问题排查结果 #

共两处问题，修复后问题解决：

1. 语法不符合规范：执行语句display.setText(text);直接写在类作用域下，Java要求可执行语句必须放在方法、构造器或代码块中，FXML组件注入完成后需要执行的初始化操作可以放在initialize()方法中。
2. FXML绑定错误：FXML文件中Label组件使用id="display"声明，而@FXML注解依赖fx:id完成组件注入，需要将Label的属性修改为fx:id="display"。

内容的提问来源于stack exchange，提问作者Atan