Question

这是一个使用fxml和netbeans的javafx的简单标签项目。问题是，当我使用

时

StartFomulars.setText("abc");

下面给出了一个例外情况。

以下是main的代码，

package main;

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


public class Start extends Application {

    @Override
    public void start(Stage stage) throws Exception {
        Prove Controller = new Prove();
        Controller.launchController(stage);
    }

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

}

fxml，

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

<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.paint.*?>

<AnchorPane id="AnchorPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="720.0" prefWidth="1080.0" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2">
  <children>
    <GridPane layoutX="0.0" layoutY="0.0" prefHeight="720.0" prefWidth="1080.0">
      <children>
        <GridPane GridPane.columnIndex="0" GridPane.rowIndex="0">
          <columnConstraints>
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
          </columnConstraints>
          <rowConstraints>
            <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
            <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
          </rowConstraints>
        </GridPane>
        <GridPane GridPane.columnIndex="1" GridPane.rowIndex="1">
          <children>
            <GridPane GridPane.columnIndex="0" GridPane.rowIndex="0">
              <columnConstraints>
                <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
                <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
              </columnConstraints>
              <rowConstraints>
                <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
                <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
                <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
                <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
                <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
              </rowConstraints>
            </GridPane>
          </children>
          <columnConstraints>
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
          </columnConstraints>
          <rowConstraints>
            <RowConstraints maxHeight="282.0" minHeight="10.0" prefHeight="282.0" vgrow="SOMETIMES" />
            <RowConstraints maxHeight="281.0" minHeight="10.0" prefHeight="281.0" vgrow="SOMETIMES" />
          </rowConstraints>
        </GridPane>
        <GridPane GridPane.columnIndex="0" GridPane.rowIndex="1">
          <children>
            <Label text="Given: " GridPane.columnIndex="0" GridPane.rowIndex="0" />
            <Label text="Prove: " GridPane.columnIndex="0" GridPane.rowIndex="1" />
            <Label text="Goal: " GridPane.columnIndex="0" GridPane.rowIndex="2" />
            <Label fx:id="StartFomulars" text="StartFomulars" GridPane.columnIndex="1" GridPane.rowIndex="0" />
            <Label fx:id="GoalFomular" text="GoalFomular" GridPane.columnIndex="1" GridPane.rowIndex="2" />
          </children>
          <columnConstraints>
            <ColumnConstraints hgrow="SOMETIMES" maxWidth="457.0" minWidth="10.0" prefWidth="125.0" />
            <ColumnConstraints hgrow="SOMETIMES" maxWidth="802.0" minWidth="10.0" prefWidth="790.0" />
          </columnConstraints>
          <rowConstraints>
            <RowConstraints maxHeight="188.0" minHeight="10.0" prefHeight="156.0" vgrow="SOMETIMES" />
            <RowConstraints maxHeight="364.0" minHeight="10.0" prefHeight="364.0" vgrow="SOMETIMES" />
            <RowConstraints maxHeight="186.0" minHeight="10.0" prefHeight="43.0" vgrow="SOMETIMES" />
          </rowConstraints>
        </GridPane>
      </children>
      <columnConstraints>
        <ColumnConstraints hgrow="SOMETIMES" maxWidth="915.0" minWidth="10.0" prefWidth="915.0" />
        <ColumnConstraints hgrow="SOMETIMES" maxWidth="539.0" minWidth="10.0" prefWidth="165.0" />
      </columnConstraints>
      <rowConstraints>
        <RowConstraints maxHeight="359.0" minHeight="10.0" prefHeight="157.0" vgrow="SOMETIMES" />
        <RowConstraints maxHeight="582.0" minHeight="10.0" prefHeight="563.0" vgrow="SOMETIMES" />
      </rowConstraints>
    </GridPane>
  </children>
</AnchorPane>

这是控制器的代码，

package main;

import ast.LogicStatement;
import java.io.IOException;
import java.util.List;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.stage.Stage;

/**
 *
 * @author zl2511
 */
public class Prove {

    private Parent parent;
    private Scene scene;
    private Stage stage;
    private List<LogicStatement> startStatements; 
    private LogicStatement goalStatement;

    @FXML
    private Label StartFomulars, GoalFomular; 

    public Prove() throws IOException { 

        FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("Prove.fxml"));
        //fxmlLoader.setController(this);
        try {
            parent = (Parent) fxmlLoader.load();

            scene = new Scene(parent);
        } catch (IOException e) {
        }

        StartFomulars.setText("abc");

    }


    public void launchController(Stage stage) {

        this.stage = stage;
        stage.setTitle("start");
        stage.setScene(scene);
        stage.setResizable(true);
        stage.hide();
        stage.show();

    }

    public void redirectprove(Stage stage, List<LogicStatement> startFormulas, LogicStatement goalFormula) { 

        this.startStatements = startFormulas; 
        this.goalStatement = goalFormula; 

        stage.setScene(scene);
        stage.hide();
        stage.show();

    }
}

以下是例外，

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:483)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:367)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:305)
    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:483)
    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:894)
    at com.sun.javafx.application.LauncherImpl.access$000(LauncherImpl.java:56)
    at com.sun.javafx.application.LauncherImpl$1.run(LauncherImpl.java:158)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException

Answer 1

你的结构很不寻常。构造Application类，FXML文件和控制器更为正常，如tutorial所示。

正如您设置的那样，您的控制器类和FXML之间没有任何关联。因此注释@FXML的字段永远不会被初始化。

这意味着工作的方式是FXMLLoader的{{1}}方法将解析FXML文件。如果在加载器上设置了控制器，则定义了load(...)属性的任何元素将被注入到控制器中匹配的fx:id带注释的字段中。

基本上有两种方法可以在@FXML上设置控制器。第一种是在FXML文件的根元素上定义FXMLLoader属性。这将导致FXML加载程序创建指定类的新实例，并将其用作其控制器。请注意，这不适用于您的情况，因为您希望控制器是您已创建的fx:controller实例，而不是Prove类的新实例。

第二种方法是创建Prove实例（而不是依赖于您当前使用的FXMLLoader static方法），并在该实例上调用FXMLLoader.load(URL)。所以（我认为）取消注释

setController(...)

行将使这个工作。

您可能还需要分隔字段的声明，即：

//fxmlLoader.setController(this);

（如果没有这种改变，它可能会有效，我从未尝试过你的方式。）

您可能还应该在@FXML private Label StartFomulars ; @FXML private Label GoalFomular;的构造函数中取出try {...} catch (...) {...}结构（因为无论如何都要声明它Prove），或者至少在throws IOException中执行某些操作块。现在，如果加载FXML会发生异常，你就不会知道它了，你只需继续前进并尝试设置标签的文本。

当我尝试更改标签的文本值时，java.lang.reflect.InvocationTargetException

1 个答案: