Question

我需要帮助将main.view.fxml中标签的文本设置为当前的小时，分钟和秒，因为它会抛出一个空指针异常

What I tried so far:
Calendar calendar = new GregorianCalendar();
HRS_lbl.setText(String.valueOf(calendar.get(Calendar.HOUR)));
MIN_lbl.setText(String.valueOf(calendar.get(Calendar.MINUTE)));
SEC_lbl.setText(String.valueOf(calendar.get(Calendar.SECOND)));

但它不起作用......

这是我的fxml文件

<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.effect.Blend?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.FlowPane?>
<?import javafx.scene.paint.LinearGradient?>
<?import javafx.scene.paint.Stop?>
<?import javafx.scene.text.Font?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="209.0" prefWidth="758.0" style="-fx-background-color: #227B89;" xmlns="http://javafx.com/javafx/9.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="lecture.application.mainViewController">
   <children>
      <FlowPane orientation="VERTICAL" prefHeight="209.0" prefWidth="273.0" style="-fx-background-color: #1F1F1F;" AnchorPane.leftAnchor="0.0">
         <effect>
            <Blend />
         </effect>
         <children>
            <AnchorPane prefHeight="209.0" prefWidth="276.0">
               <children>
                  <Label layoutX="65.0" layoutY="80.0" text="The Clock">
                     <font>
                        <Font size="34.0" />
                     </font>
                     <textFill>
                        <LinearGradient endX="1.0" endY="1.0">
                           <stops>
                              <Stop color="#e0e3ebcc" />
                              <Stop color="#e0e3ebcc" offset="0.32950191570881227" />
                              <Stop color="WHITE" offset="1.0" />
                           </stops>
                        </LinearGradient>
                     </textFill>
                  </Label>
               </children>
            </AnchorPane>
         </children>
      </FlowPane>
      <Label fx:id="HRS_lbl" layoutX="360.0" layoutY="49.0" text="00">
         <font>
            <Font name="Consolas Bold" size="35.0" />
         </font>
         <padding>
            <Insets left="20.0" top="20.0" />
         </padding>
      </Label>
      <Label fx:id="MIN_lbl" layoutX="453.0" layoutY="49.0" text="00">
         <font>
            <Font name="Consolas Bold" size="35.0" />
         </font>
         <padding>
            <Insets left="20.0" top="20.0" />
         </padding>
      </Label>
      <Label fx:id="SEC_lbl" layoutX="559.0" layoutY="49.0" prefHeight="61.0" prefWidth="82.0" text="00">
         <font>
            <Font name="Consolas Bold" size="35.0" />
         </font>
         <padding>
            <Insets left="20.0" top="20.0" />
         </padding>
      </Label>
      <Label layoutX="390.0" layoutY="123.0" text="HRS" />
      <Label layoutX="483.0" layoutY="117.0" prefHeight="30.0" prefWidth="28.0" text="MIN" />
      <Label layoutX="591.0" layoutY="123.0" text="SEC" />
      <Button fx:id="exit_btn" layoutX="690.0" layoutY="6.0" mnemonicParsing="false" text="Exit" textFill="#000000fa" />
   </children>
   <opaqueInsets>
      <Insets />
   </opaqueInsets>
</AnchorPane>

这是显示的错误 此警告是否至关重要：警告：使用JavaFX API加载FXML文档版本9.0.1由JavaFX运行时版本8.0.161

Apr 23, 2018 10:34:47 PM javafx.fxml.FXMLLoader$ValueElement processValue
WARNING: Loading FXML document with JavaFX API of version 9.0.1 by JavaFX runtime of version 8.0.161
Exception in Application start method
java.lang.NullPointerException
    at lecture.application.mainViewController$1.run(mainViewController.java:39)
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.launcher.LauncherHelper$FXHelper.main(Unknown Source)
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$154(LauncherImpl.java:182)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
    at lecture.application.mainViewController.setTime(mainViewController.java:51)
    at lecture.application.Main.start(Main.java:41)
    at com.sun.javafx.application.LauncherImpl.lambda$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

这是主要类

所以错误从第39行开始，我开始将setText设置为我的fxml文件中的标签

private Stage primaryStage;
private AnchorPane mainLayout;
double x;
double y;   

@Override
public void start(Stage primaryStage) throws IOException {
    this.primaryStage = primaryStage;
    this.primaryStage.setTitle("The Clock ");
    this.primaryStage.setResizable(true);
    this.primaryStage.setMaximized(false);
    this.primaryStage.setAlwaysOnTop(false);
    this.primaryStage.initStyle(StageStyle.UNDECORATED);
    mainViewController controler = new mainViewController();

    primaryStage.maximizedProperty().addListener((observable, oldValue, newValue) -> {
        if (newValue)
            primaryStage.setMaximized(false);
    });
    showMainView();
    controler.setTime();
    setDrag();
}

private void showMainView() throws IOException {
    try {
        FXMLLoader loader = new FXMLLoader();
        loader.setLocation(Main.class.getResource("main.view.fxml"));
        mainLayout = loader.load();

        Scene scene = new Scene(mainLayout);
        primaryStage.setScene(scene);
        primaryStage.show();}

    catch(Exception e) {
        JOptionPane.showMessageDialog(null, e.getMessage());
        e.printStackTrace();
    }
}

void setDrag() {     
    mainLayout.setOnMousePressed(new EventHandler<MouseEvent>() {

        @Override
        public void handle(MouseEvent arg0) {
            x = arg0.getSceneX();
            y = arg0.getSceneY();
        }
    });

    mainLayout.setOnMouseDragged(new EventHandler<MouseEvent>() {

        @Override
        public void handle(MouseEvent event) {
            primaryStage.setX(event.getSceneX() - x);
            primaryStage.setY(event.getSceneY() - y);
        }
    });  
}

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

这是fxml控制器类

@FXML
private Label HRS_lbl;

@FXML
private Label MIN_lbl;

@FXML
private Label SEC_lbl;

@FXML
private Button exit_btn;

void setTime() {
    new Thread () {
        public void run() {
            try {
                Calendar calendar = new GregorianCalendar();
                HRS_lbl.setText(String.valueOf(calendar.get(Calendar.HOUR)));
                MIN_lbl.setText(String.valueOf(calendar.get(Calendar.MINUTE)));
                SEC_lbl.setText(String.valueOf(calendar.get(Calendar.SECOND)));
            } catch (Exception e) {
                e.getMessage();
                e.printStackTrace();
            }
        }
    }.start();

    exit_btn.setOnAction(new javafx.event.EventHandler<ActionEvent>() {

        @Override
        public void handle(ActionEvent event) {
            JOptionPane.showMessageDialog(null, "Thank you for using The Clock...... developed By Tawanda Mavondo");
        }
    });
}

Answer 1

关于你的控制器

*您为控制器取一个对象，但它的引用与您的VIEW（FXML）无关

你可以在控制器中添加你想要做的任何事情，并使用初始化函数，该函数在渲染视图之后开始，这意味着它将立即开始。

@Override
public void initialize(URL url, ResourceBundle rb) {
        // TODO
setTime() ;
}

我测试它工作正常

注意：您正在使用MVC设计模式。

如何修复空指针异常

1 个答案: