java将嵌套对象从fxml映射到对象

Question

我创建了以下对象，它应该负责在我的win应用程序中显示steeringwheel

@DefaultProperty("children")
public class SteeringWheel extends Region {
    @FXML
    private Circle backgroundCircle;
    @FXML
    private Circle innerCircle;
    @FXML
    private Label mylabel;

    public ObservableList<Node> getChildren() {
        return super.getChildren();
    }


    public void setCirclesLocations() {
        double centerPointX = getWidth() / 2;
        double centerPointY = getHeight() / 2;

        setCircleLocation(backgroundCircle, centerPointX, centerPointY);
        setCircleLocation(innerCircle, centerPointX, centerPointY);
    }

    private void setCircleLocation(Circle c, double x, double y) {
        c.setCenterX(x);
        c.setCenterY(y);
    }

我的fxml文件包含以下内容：

<BorderPane xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/9.0.1" fx:controller="view.WindowController">

   <center>
      <VBox prefHeight="200" prefWidth="200" BorderPane.alignment="CENTER">
         <children>
         <SteeringWheel fx:id="steeringWheel">
            <children>
               <Label fx:id="mylabel" prefHeight="30.0" prefWidth="102.0" text="aileron"  />
             
          <Circle fx:id="innerCircle" fill="black" radius="40" />
          <Circle fx:id="backgroundCircle" fill="darkgray" radius="100" />
            </children>
         </SteeringWheel>
         </children>
      </VBox>

   </center>
    .....

我试图将xml初始化映射到此对象，但它不起作用。在我的主要工作中，我试图运行setCircleLocations，但我遇到了nullpointer异常

FXMLLoader fxl=new FXMLLoader();
try {
    BorderPane root = fxl.load(getClass().getResource("Window.fxml").openStream());
    
    WindowController wc=fxl.getController(); // View
    Scene scene = new Scene(root,400,400);
    scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
    primaryStage.setScene(scene);
    primaryStage.show();
    wc.steeringWheel.setCirclesLocations();



} catch (IOException e) {
    e.printStackTrace();
}

我的窗口控制器：

public class WindowController {

@FXML
SteeringWheel steeringWheel;
}

此外，在xml文件中，我得到了SteeringWheel的子级的以下错误：Unresolved fx:id reference

堆栈跟踪：

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:473)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:372)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:973)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:198)
    at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.lang.NullPointerException
    at view.WheelingSteer.setCircleLocation(WheelingSteer.java:36)
    at view.WheelingSteer.setCirclesLocations(WheelingSteer.java:31)
    at view.Main.start(Main.java:33)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:919)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$11(PlatformImpl.java:449)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$9(PlatformImpl.java:418)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:417)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:175)
    ... 1 more
Exception running application view.Main

Answer 1

只有控制器注入了适当的字段。你的SteeringWheel类不是控制器，因此那些@FXML注释的字段不会被注入。但是，您打算注入这些字段的对象被放入children列表中，因此您可以在那里访问它们。然而，似乎您希望SteeringWheel成为它自己的组件，其中两个Circle和Label始终存在，无论SteeringWheel如何使用，因此尝试在单独的位置定义子级是没有意义的

既然您正在扩展^ {< CD8>}，您可能需要考虑使用^ a1}:

import java.io.IOException;
import java.io.UncheckedIOException;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.geometry.HPos;
import javafx.geometry.VPos;
import javafx.scene.control.Label;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Circle;

public class SteeringWheel extends Pane {

  @FXML private Label myLabel;
  @FXML private Circle innerCircle;
  @FXML private Circle backgroundCircle;

  public SteeringWheel() {
    FXMLLoader loader = new FXMLLoader(/* location */);
    loader.setRoot(this);
    loader.setController(this);
    try {
      loader.load();
    } catch (IOException ex) {
      throw new UncheckedIOException(ex);
    }
  }

  @FXML
  private void initialize() {
    // perform any initialization, if needed
  }

  @Override
  public void layoutChildren() {
    // Note: I didn't implement checking if the nodes are managed
    //       before laying them out. You may wish to add that
    //       behavior.


    // The following will always keep the Circles in the center
    // of the Pane. However, it does this by setting the layout[X|Y]
    // properties rather than the center[X|Y] properties (as you're
    // doing).
    double x = snappedLeftInset();
    double y = snappedTopInset();
    double w = getWidth() - snappedRightInset() - x;
    double h = getHeight() - snappedBottomInset() - y;

    positionInArea(innerCircle, x, y, w, h, -1, HPos.CENTER, VPos.CENTER);
    positionInArea(backgroundCircle, x, y, w, h, -1, HPos.CENTER, VPos.CENTER);

    // Layout the Label in the top-left corner
    layoutInArea(myLabel, x, y, w, h, -1, HPos.LEFT, VPos.TOP);
  }
}

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Label?>
<?import javafx.scene.shape.Circle?>

<fx:root type="javafx.scene.layout.Pane" xmlns="http://javafx.com/javafx/9.0.1" 
         xmlns:fx="http://javafx.com/fxml/1">
  <Label fx:id="myLabel" text="Hello, World!"/>
  <Circle fx:id="backgroundCircle" radius="30" fill="BLACK"/>
  <Circle fx:id="innerCircle" radius="25" fill="FIREBRICK"/>
</fx:root>

注意：我扩展了Pane而不是Region。前者已经扩展了后者，并且已经进行了您所做的更改（即，将#getChildren()方法公开，并添加@DefaultProperty("children")注释）

注意：我覆盖了#layoutChildren()，这样无论父对象最终的维度是什么，您的圆都保持在中心。然而，简单地将它们包装在其他一些布局中可能更容易，例如StackPane

然后在另一个FXML文件中使用SteeringWheel：

<BorderPane xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/9.0.1" fx:controller="view.WindowController">

   <center>
      <VBox prefHeight="200" prefWidth="200" BorderPane.alignment="CENTER">
         <children>
            <SteeringWheel fx:id="steeringWheel"/>
         </children>
      </VBox>

   </center>
    .....