按钮在fxml中返回空指针

Question

我在尝试使用JavaFX时遇到按钮问题。我正在尝试为按钮设置自定义字体。当我试图更改按钮的字体时，程序崩溃了。

堆栈上的其他主题似乎没有帮助，因为它们似乎没有同样的问题。对不起，如果还有其他话题，但我不理解修复程序，因为我是JavaFX的新手。提前感谢您的帮助。

这是我的代码

import javafx.application.Application;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.text.Font;
import javafx.stage.Stage;
import java.io.FileInputStream;
public class Main extends Application {
@Override
public void start(Stage primaryStage) throws Exception{
FXMLLoader loader = new FXMLLoader();
String fxmlDocPath = "C:\Users\Mihai\Documents\GitHub\Kitchen3\src\sample\sample.fxml";
FileInputStream fxmlStream = new FileInputStream(fxmlDocPath);
Parent root = loader.load(getClass().getResource("sample.fxml"));
//Setting the stage and adding my custom style to it
primaryStage.setTitle("Hello World");
root.getStylesheets().add("sample/style.css");
root.setId("pane");
Controller controller = new Controller();
loader.setController(controller);
Font defaultFont = Font.loadFont(getClass().getResourceAsStream("/Aclonica.woff2"), 16);
controller.homeButton.setFont(defaultFont);
primaryStage.setScene(new Scene(root, 800 , 600));
primaryStage.show();
}

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

这是我的fxml文件：

<?import javafx.scene.canvas.Canvas?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.ButtonBar?>
<?import javafx.scene.layout.BorderPane?>
<BorderPane id="pane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="600.0" prefWidth="800.0" xmlns="http://javafx.com/javafx/8.0.172-ea" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
<center>
<Canvas height="560.0" width="800.0" BorderPane.alignment="CENTER" />
</center>
<top>
<ButtonBar prefHeight="40.0" prefWidth="200.0" BorderPane.alignment="CENTER">
<buttons>
<Button fx:id="homeButton" id="button" mnemonicParsing="false" text="Home" />
</buttons>
</ButtonBar>
</top>
</BorderPane>

这是我的控制器

import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.text.Font;
public class Controller {
@FXML
Button homeButton;
@FXML
BorderPane pane;
public Controller(){
}
@FXML
public void initialize(){
//I have tried this to see if it would help.
homeButton.setText("Home");
Font default = Font.getDefault();
homeButton.setFont(arial);
}
@FXML
public Button getHomeButton() {
return homeButton;
}
@FXML
public void setHomeButton(Button homeButton) {
this.homeButton = homeButton;
}
}

Stacktrace:

java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$154(LauncherImpl.java:182)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
at com.sun.javafx.scene.control.skin.Utils.computeTextHeight(Utils.java:130)
at com.sun.javafx.scene.control.skin.LabeledSkinBase.computeMinLabeledPartHeight(LabeledSkinBase.java:707)
at com.sun.javafx.scene.control.skin.LabeledSkinBase.computeMinHeight(LabeledSkinBase.java:689)
at javafx.scene.control.Control.computeMinHeight(Control.java:489)
at javafx.scene.Parent.minHeight(Parent.java:957)
at javafx.scene.layout.Region.minHeight(Region.java:1401)
at javafx.scene.layout.Region.computeChildMinAreaHeight(Region.java:1697)
at javafx.scene.layout.Region.getMaxAreaHeight(Region.java:1978)
at javafx.scene.layout.Region.computeMaxMinAreaHeight(Region.java:1847)
at javafx.scene.layout.HBox.computeMinHeight(HBox.java:415)
at javafx.scene.Parent.minHeight(Parent.java:957)
at javafx.scene.layout.Region.minHeight(Region.java:1401)
at javafx.scene.control.SkinBase.computeMinHeight(SkinBase.java:254)
at javafx.scene.control.Control.computeMinHeight(Control.java:489)
at javafx.scene.Parent.minHeight(Parent.java:957)
at javafx.scene.layout.Region.minHeight(Region.java:1401)
at javafx.scene.layout.Region.boundedNodeSizeWithBias(Region.java:1917)
at javafx.scene.layout.BorderPane.layoutChildren(BorderPane.java:517)
at javafx.scene.Parent.layout(Parent.java:1087)
at javafx.scene.Scene.doLayoutPass(Scene.java:552)
at javafx.scene.Scene.preferredSize(Scene.java:1646)
at javafx.scene.Scene.impl_preferredSize(Scene.java:1720)
at javafx.stage.Window$9.invalidated(Window.java:864)
at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:109)
at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:144)
at javafx.stage.Window.setShowing(Window.java:940)
at javafx.stage.Window.show(Window.java:955)
at javafx.stage.Stage.show(Stage.java:259)
at sample.Main.start(Main.java:25)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$161(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$174(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$172(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$173(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
... 1 more
Exception running application sample.Main
Process finished with exit code 1 ```

Answer 1

即使您提供的代码甚至不应该编译，我猜以下是您的问题：

您通过fx:Controller指定了控制器，但也在代码中覆盖了它。新实例是在加载后指定的，因此不知道控件的实例。

从您的fxml中删除fx:controller部分，并在(！(调用loader.load(…(之前设置控制器

或者参考现有的控制器，而不是设置一个新的