无法调用“javafx.scene.control.TableColumn.setCellValueFactory(javafx.util.Callback)”，因为“this.colName”为空

问题描述 投票：0回答：1

所以我的问题是我无法将数据显示到表格视图，我不明白为什么 我有一个表单使用 ProductController 和显示 tableview 方法，在另一个控制器 CardProductContrller 中，我在 addFcn 方法中调用 ProductController 中的方法，它返回错误:

无法调用 

javafx.scene.control.TableColumn.setCellValueFactory(javafx.util.Callback)
，因为 
this.colName
为 null

这里有更详细的错误：

java.lang.NullPointerException: Cannot invoke "javafx.scene.control.TableColumn.setCellValueFactory(javafx.util.Callback)" because "this.colName" is null
    at application.ProductController.showOrderDetail(ProductController.java:409)
    at application.CardProdController.addFcn(CardProdController.java:169)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:72)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at javafx.base@21/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:270)
    at javafx.fxml@21/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
    at javafx.fxml@21/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1855)
    at javafx.fxml@21/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1726)
    at javafx.base@21/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base@21/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:232)
    at javafx.base@21/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:189)
    at javafx.base@21/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base@21/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.base@21/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics@21/javafx.scene.Node.fireEvent(Node.java:8875)
    at javafx.controls@21/javafx.scene.control.Button.fire(Button.java:203)
    at javafx.controls@21/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:207)
    at javafx.controls@21/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
    at javafx.base@21/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
    at javafx.base@21/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at javafx.base@21/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:232)
    at javafx.base@21/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:189)
    at javafx.base@21/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@21/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@21/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base@21/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base@21/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics@21/javafx.scene.Scene$MouseHandler.process(Scene.java:3984)
    at javafx.graphics@21/javafx.scene.Scene.processMouseEvent(Scene.java:1890)
    at javafx.graphics@21/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2708)
    at javafx.graphics@21/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
    at javafx.graphics@21/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
    at javafx.graphics@21/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
    at javafx.graphics@21/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
    at javafx.graphics@21/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
    at javafx.graphics@21/com.sun.glass.ui.View.handleMouseEvent(View.java:551)
    at javafx.graphics@21/com.sun.glass.ui.View.notifyMouse(View.java:937)
    at javafx.graphics@21/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics@21/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:185)
    at java.base/java.lang.Thread.run(Thread.java:1583)

这里的代码： 卡产品控制器：

package application;

import java.net.URL;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Date;
import java.util.Optional;
import java.util.ResourceBundle;

import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.scene.control.Button;
import javafx.scene.control.ButtonType;
import javafx.scene.control.Label;
import javafx.scene.control.Spinner;
import javafx.scene.control.SpinnerValueFactory;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.BorderPane;

public class CardProdController implements Initializable {

    @FXML
    private Button addBtn;

    @FXML
    private BorderPane cardForm;

    @FXML
    private ImageView imageView;

    @FXML
    private Label name;

    @FXML
    private Label price;

    @FXML
    private Spinner<Integer> quantity;
    
    private productModel productM;
    
    private Image image;
    
    private String proId;
    private String pro_image;
    private String pro_date;
    
    private SpinnerValueFactory<Integer> spin;
    
    @FXML 
    private Connection connection;
    private PreparedStatement prepare;
    private ResultSet result;
    private Alert alert;

    private double pr;
    private int cusId;
    
    public void setData(productModel productM) {
        this.productM = productM;
        
        pro_image = productM.getProductImage();
        pro_date = String.valueOf(productM.getDate());
        proId = productM.getProductId();
        name.setText(productM.getProductName());
        price.setText(String.valueOf(productM.getProductPrice()));
        String path = "File:" + productM.getProductImage();
        image = new Image(path, 190, 130, false, true);
        imageView.setImage(image);
        pr = productM.getProductPrice();

    }
    
    private int qty;
    private double totalP;
    private String ordDID;
    public void addFcn() throws SQLException {
            ProductController pC = new ProductController();
            pC.customerID(); 
            pC.order_detailID();
            qty = quantity.getValue();
            String check = "";
            String checkAvailable = "SELECT pro_status FROM product WHERE pro_id = '" + proId + "'";
            
            connection = Database.connect();
            try {
                int checkS = 0;
                String checkStock = "SELECT pro_quantity FROM product WHERE pro_id = '" + proId + "'";

                prepare = connection.prepareStatement(checkStock);
                result = prepare.executeQuery();
                
                if(result.next()) {
                    checkS = result.getInt("pro_quantity");
                }      
                
                if(checkS == 0){
                    String updateStock = "UPDATE product SET pro_status = 'Unavailable' WHERE pro_id = '"+proId+"'";   
                    //update to database to mark it as unavailable
                    prepare = connection.prepareStatement(updateStock);
                    prepare.executeUpdate();
                }
                prepare = connection.prepareStatement(checkAvailable);
                result = prepare.executeQuery();

                if (result.next()) {
                    check = result.getString("pro_status");
                }
                if (!check.equals("Available") || qty == 0) {
                    alert = new Alert(AlertType.ERROR);
                    alert.setTitle("Error Message");
                    alert.setHeaderText(null);
                    alert.setContentText("Product currently unavalible or we run out");
                    alert.showAndWait();
                } else {
                    if (checkS < qty) {
                        alert = new Alert(AlertType.ERROR);
                        alert.setTitle("Error Message");
                        alert.setHeaderText(null);
                        alert.setContentText("Invalid. This product is Out of stock");
                        alert.showAndWait();
                    } else {
                        pro_image = pro_image.replace("\\", "\\\\");
                        
                        String insertData = "INSERT INTO order_detail "
                                + "(cus_id, ord_id, pro_id ,pro_name, pro_price, pro_quantity, orderDate) "
                                + "VALUES(?,?,?,?,?,?,?)";
                        prepare = connection.prepareStatement(insertData);
                        prepare.setString(1, String.valueOf(data.cusId));
                        
                        ordDID = data.ordDiD;
                        prepare.setString(2, ordDID);
                        prepare.setString(3, proId);
                        prepare.setString(4, name.getText());
                        
                        totalP = (qty * pr);
                        prepare.setString(5, String.valueOf(totalP));
                        prepare.setString(6, String.valueOf(qty));
                        
                        Date date = new Date();
                        java.sql.Date sqlDate = new java.sql.Date(date.getTime());
                        prepare.setString(7, String.valueOf(sqlDate));
                        
                        prepare.executeUpdate();

                        int upStock = checkS - qty;

                        String updateStock = "UPDATE product SET pro_quantity = " + upStock + " WHERE pro_id = '"+proId+"'";
                        //update product to mark it's quantity as decreased as being order by customer 
                        prepare = connection.prepareStatement(updateStock);
                        prepare.executeUpdate();
                        
                        alert = new Alert(AlertType.INFORMATION);
                        alert.setTitle("Information Message");
                        alert.setHeaderText(null);
                        alert.setContentText("Successfully Added!");
                        Optional<ButtonType> option = alert.showAndWait();
                        
                        if(option.get().equals(ButtonType.OK)) {
                            
                            
                            pC.showOrderDetail();
                        }
                        //pC.menuGetTotal();//tinh sau
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }   
        }
    
    public void setQuantity() {
        spin = new SpinnerValueFactory.IntegerSpinnerValueFactory(1, 100, 0);
        quantity.setValueFactory(spin);
    }
    
    @Override
    public void initialize(URL arg0, ResourceBundle arg1) {
        setQuantity();
    }
    
}

产品控制器：

package application;

import java.io.IOException;
import java.net.URL;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Optional;
import java.util.ResourceBundle;

import com.mysql.cj.x.protobuf.MysqlxCrud.Column;

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.geometry.Insets;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.scene.control.Button;
import javafx.scene.control.ButtonType;
import javafx.scene.control.Label;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;

public class ProductController implements Initializable{
    @FXML
    private GridPane gridProd;

    @FXML
    private Button clBtn;

    @FXML
    private Button doneBtn;
 
    @FXML
    private Button clrBtn;

    @FXML
    private TableColumn<order_detailModel, String> colName;

    @FXML
    private TableColumn<order_detailModel, String> colPrice;

    @FXML
    private TableColumn<order_detailModel, String> colQuantity;
    
    @FXML
    private TableView<order_detailModel> orderView;
    
    @FXML
    private Button payBtn;

    @FXML
    private Button printBillBtn;

    @FXML
    private Label totalBill;
    
    @FXML 
    private Connection connection;
    private PreparedStatement prepare;
    private ResultSet result;
    private Alert alert;
    
    @FXML
    private Stage sideStage;
    private Scene scene;
    private Parent root;

    private int cID;
    public void customerID() throws SQLException {
         String sql = "SELECT MAX(cus_id) FROM customer";
         connection = Database.connect();
         
         try {
             prepare = connection.prepareStatement(sql);
             result = prepare.executeQuery();
             if (result.next()) {
                 cID = result.getInt("MAX(cus_id)");
             }
             String checkCID = "SELECT MAX(cus_id) FROM receipt";
             prepare = connection.prepareStatement(checkCID);
             result = prepare.executeQuery();
             int checkID = 0;
             if (result.next()) {
                 checkID = result.getInt("MAX(cus_id)");
             }
             if (cID == 0) {
                 cID += 1;
             } else if (cID == checkID) {
                 cID += 1;
             }
             data.cusId = cID;
         } catch (Exception e) {
             e.printStackTrace();
         }
    }
    
    private String odID;
    public void order_detailID() throws SQLException {
     String sql = "SELECT MAX(ord_id) FROM order_detail";
        connection = Database.connect();
        
        try {
            prepare = connection.prepareStatement(sql);
            result = prepare.executeQuery();
            if (result.next()) {
                odID = result.getString("MAX(ord_id)");
            }
            String checkODID = "SELECT MAX(ord_id) FROM receipt ";
            prepare = connection.prepareStatement(checkODID);
            result = prepare.executeQuery();
            String checkID = null;
            if (result.next()) {
                checkID = result.getString("MAX(ord_id)");
            }
            if (odID == null) {
                String aIM = "ORD-" + 0;
                odID = aIM + 1;
            } else if (odID == checkID) {
                String aIM = "ORD-" + 0;
                odID = aIM + 1;
            }
            data.ordDiD = odID;
            System.out.println(data.ordDiD);
        } catch (Exception e) {
            e.printStackTrace();
        }
   }
    

       private ObservableList<productModel> cardDataList = FXCollections.observableArrayList();
        
        public ObservableList<productModel> getData(){
            
            ObservableList<productModel> ListData = FXCollections.observableArrayList();
            
            String getData = "SELECT * FROM product";
            try {
                connection = Database.connect();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            try {
                prepare = connection.prepareStatement(getData);
                result = prepare.executeQuery();
                
                productModel productM;
                
                while(result.next()) {
                    productM = new productModel(result.getInt("id")
                                                ,result.getString("pro_id")
                                                , result.getString("pro_name")
                                                , result.getDouble("pro_price")
                                                , result.getInt("pro_quantity")
                                                , result.getString("pro_image"));
                    ListData.add(productM);
                }
            }catch (SQLException e) {
                // TODO: handle exception
                e.printStackTrace();
            }
            return ListData;
        }
        
        public void menuProd() {
            cardDataList.clear();
            cardDataList.addAll(getData());
            
            int row = 0; 
            int column = 0;
            gridProd.getChildren().clear();
            gridProd.getRowConstraints().clear();
            gridProd.getColumnConstraints().clear();
            
            for(int i  = 0; i < cardDataList.size(); i++) {
                try {
                    FXMLLoader loader = new FXMLLoader();
                    loader.setLocation(getClass().getResource("cardProduct.fxml"));
                    Pane pane = loader.load();
                    CardProdController cpC = loader.getController();
                    cpC.setData(cardDataList.get(i));
                    
                    if(column == 3) {
                        column = 0;
                        row += 1;
                    }
                    
                    gridProd.add(pane, column++, row);
                    
                    GridPane.setMargin(pane, new Insets(10));
                }catch (IOException e) {
                    // TODO: handle exception
                    e.printStackTrace();
                }
            }
        }
        
        public void clFcn(ActionEvent event) throws IOException {
            
            root = FXMLLoader.load(getClass().getResource("StaffSection.fxml"));
            sideStage = (Stage)((Node)event.getSource()).getScene().getWindow();
            scene = new Scene(root);
            sideStage.setScene(scene);
            sideStage.setResizable(false);
            sideStage.show();
        }
        
        public void doneFcn(ActionEvent event) throws IOException {
            
            root = FXMLLoader.load(getClass().getResource("StaffSection.fxml"));
            sideStage = (Stage)((Node)event.getSource()).getScene().getWindow();
            scene = new Scene(root);
            sideStage.setScene(scene);
            sideStage.setResizable(false);
            sideStage.show();
        }
        
        public ObservableList<order_detailModel> orderDList() throws SQLException {
               ObservableList<order_detailModel> oList = FXCollections.observableArrayList();
               
               String getData = "SELECT pro_name, pro_price, pro_quantity FROM order_detail";
               connection = Database.connect();
               try {
                    prepare = connection.prepareStatement(getData);
                    result = prepare.executeQuery();
                    
                    order_detailModel ordDM;
                    while(result.next()) {
                        ordDM = new order_detailModel(result.getString("pro_name")
                                                        ,result.getDouble("pro_price")
                                                        ,result.getInt("pro_quantity"));
                        oList.add(ordDM);
                    }
               }catch (Exception e) {
                e.printStackTrace();
                System.out.println(e.getMessage());
            }
            return oList; 
        }
        
        ObservableList<order_detailModel> listOrdD;
        public void showOrderDetail() {
            try {
                
                listOrdD = orderDList();
                
                colName.setCellValueFactory(new PropertyValueFactory<>("pro_name"));
                colPrice.setCellValueFactory(new PropertyValueFactory<>("pro_price"));
                colQuantity.setCellValueFactory(new PropertyValueFactory<>("pro_quantity"));
                
                orderView.setItems(listOrdD);
                
            }catch (Exception e) {
                e.printStackTrace();
                e.getMessage();
            }
        }

    @Override
    public void initialize(URL arg0, ResourceBundle arg1) {
        getData();
        menuProd();
    }
}

FXML 文件使用 Productcontroller :

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

<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.ScrollPane?>
<?import javafx.scene.control.TableColumn?>
<?import javafx.scene.control.TableView?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.Pane?>
<?import javafx.scene.layout.RowConstraints?>
<?import javafx.scene.text.Font?>

<BorderPane prefHeight="700.0" prefWidth="1200.0" stylesheets="@CSS/TableServe.css" xmlns="http://javafx.com/javafx/21" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.ProductController">
   <center>
      <AnchorPane prefHeight="200.0" prefWidth="200.0" BorderPane.alignment="CENTER">
         <children>
            <AnchorPane fx:id="acPane1" layoutX="15.0" layoutY="15.0" prefHeight="670.0" prefWidth="750.0">
               <children>
                  <ScrollPane layoutX="15.0" layoutY="15.0" prefHeight="640.0" prefWidth="720.0">
                     <content>
                        <GridPane fx:id="gridProd" hgap="10.0" prefHeight="879.0" prefWidth="680.0" vgap="10.0">
                          <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>
                          <rowConstraints>
                            <RowConstraints fillHeight="false" minHeight="10.0" prefHeight="100.0" vgrow="SOMETIMES" />
                            <RowConstraints minHeight="10.0" prefHeight="100.0" vgrow="SOMETIMES" />
                            <RowConstraints minHeight="10.0" prefHeight="100.0" vgrow="SOMETIMES" />
                              <RowConstraints minHeight="10.0" prefHeight="100.0" vgrow="SOMETIMES" />
                          </rowConstraints>
                        </GridPane>
                     </content>
                     <padding>
                        <Insets bottom="10.0" left="10.0" right="10.0" top="10.0" />
                     </padding>
                  </ScrollPane>
               </children>
            </AnchorPane>
            <AnchorPane fx:id="acPane2" layoutX="785.0" layoutY="15.0" prefHeight="670.0" prefWidth="400.0">
               <children>
                  <Pane prefHeight="670.0" prefWidth="400.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
                     <children>
                        <TableView fx:id="orderView" layoutX="15.0" layoutY="14.0" prefHeight="456.0" prefWidth="370.0">
                          <columns>
                            <TableColumn fx:id="colName" prefWidth="166.4000244140625" text="Name" />
                            <TableColumn fx:id="colPrice" prefWidth="108.800048828125" text="Price" />
                              <TableColumn fx:id="colQuantity" prefWidth="93.5999755859375" text="Quantity'" />
                          </columns>
                        </TableView>
                        <Button fx:id="payBtn" layoutX="10.0" layoutY="566.0" mnemonicParsing="false" prefWidth="120.0" text="Pay" />
                        <Button fx:id="printBillBtn" layoutX="270.0" layoutY="566.0" mnemonicParsing="false" prefWidth="120.0" text="Print BIll" />
                        <Button fx:id="clrBtn" layoutX="140.0" layoutY="566.0" mnemonicParsing="false" prefWidth="120.0" text="Clear" />
                        <Button fx:id="clBtn" layoutX="225.0" layoutY="629.0" mnemonicParsing="false" onAction="#clFcn" prefHeight="30.0" prefWidth="160.0" text="Cancel" />
                        <Button fx:id="doneBtn" layoutX="17.0" layoutY="629.0" mnemonicParsing="false" onAction="#doneFcn" prefHeight="30.0" prefWidth="160.0" text="Done" />
                        <Label fx:id="totalBill" layoutX="17.0" layoutY="489.0" prefHeight="30.0" prefWidth="173.0" text="Total: 00$$">
                           <font>
                              <Font size="20.0" />
                           </font>
                        </Label>
                     </children>
                  </Pane>
               </children>
            </AnchorPane>
         </children>
      </AnchorPane>
   </center>
</BorderPane>

我几乎做了所有事情，使用chatgpt得到了ofc的帮助，但仍然不知道为什么，我认为我的sql是错误的？

java javafx nullpointerexception
1个回答
0
投票

切勿在 FXML 文件中指定的控制器上调用 

new
。

此代码错误：

ProductController pC = new ProductController();

在控制器上调用 

new
的唯一有效情况是如果这两个条件都为 true：

并且

    控制器
  • 未在 FXML 控制器中指定。
但是，你并没有做这些事情。

来自

setController

 的文档：

设置与根对象关联的控制器。传递给此方法的值用作

fx:controller

 属性的值。如果文档中未指定
fx:controller
 属性，则在使用控制器事件处理程序时，必须在加载文档之前调用此方法。

只有

FXMLLoader

 才会将控制器中的
@FXML
 带注释的字段初始化为 FXML 文件中配置的值。如果您只是在代码中创建一个新控制器，则控制器中所有带
@FXML
 注释的字段都将是
null
。

此外，如果您

也在其他地方加载了FXML，那么当您加载FXML时，加载程序将创建您在FXML中指定的控制器的实例。因此，如果您随后在控制器上调用 new，您将获得控制器的另一个实例，该实例与控制器创建的实例以及 load()

 方法返回的对象层次结构完全无关。

通常，当人们创建新控制器时，他们应该做的是：



或




    重构他们的代码，以便他们在尝试使用它的地方不需要控制器引用（例如通过
  • 应用 MVC 设计）。

    • 
    



      

      
    

  

  

    
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