java - TableView JavaFX 应用程序线程“java.lang.NullPointerException

Question

我的程序正在尝试模拟一个存储产品信息的数据库。

我正在尝试学习如何使用 TableView，但它们仍然是我不明白的东西。在我的表中，我希望能够选择多个项目并对这些项目执行某些操作。我已经做到了。

但是如果我选择第 1 行和第 2 行并右键单击“ProductName”，则会出现一个问题。然后选择第 3 行并右键单击，单击 ProductName。它给了我一个 JavaFX 应用程序线程“java.lang.NullPointerException。

我不明白它为什么这样做。如果你能帮忙请帮忙。谢谢。对不起我的英语。

package TestTableView;

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Scene;
import javafx.scene.control.ContextMenu;
import javafx.scene.control.MenuItem;
import javafx.scene.control.SelectionMode;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.layout.VBox;
import javafx.scene.web.WebEngine;
import javafx.scene.web.WebView;
import javafx.stage.Stage;
import static javafx.application.Application.launch;


public class TestTableView extends Application {
    private Stage Listwindow;
    private TableView<Product> table;  
    private String name;
    private ObservableList<Product> itemSelected;
    private WebView browser = new WebView();
    private WebEngine webEngine = browser.getEngine();

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

 @Override
    public void start(Stage primaryStage){       
        //Load UnitTable
        Listwindow = primaryStage;
        Listwindow.setTitle("Product Table");

        createTable();
        createContextMenu();

        VBox vBox = new VBox();
        vBox.getChildren().addAll(table);   
        Scene scene = new Scene(vBox);
        Listwindow.setScene(scene);
        Listwindow.show();
    }

    public void createContextMenu(){
        //Multiple selection
        table.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);


        itemSelected = table.getSelectionModel().getSelectedItems(); 

        //ContextMenu
        ContextMenu contextMenu = new ContextMenu();

        //menu items
        MenuItem item1 = new MenuItem("ProductName");

        //Add item to context menu
        contextMenu.getItems().addAll(item1);

        //set context menu to table
        table.setContextMenu(contextMenu);


        item1.setOnAction(e -> getProductName());         
    }

    public void getProductName(){
        for(int x = 0; x < itemSelected.size(); x++){
            name = itemSelected.get(x).getName();

            //do Something -> Name
        }    
        table.getSelectionModel().clearSelection();
    }    

    public void createTable(){

        TableColumn<Product, String> nameCol = new TableColumn<>("Name");
        nameCol.setMinWidth(200);
        nameCol.setCellValueFactory(new PropertyValueFactory<>("name"));

            TableColumn<Product, Double> priceCol = new TableColumn<>("Price");
            priceCol.setMinWidth(200);
            priceCol.setCellValueFactory(new PropertyValueFactory<>("price"));

            TableColumn<Product, Integer> quantityCol = new TableColumn<>("Quantity");
            quantityCol.setMinWidth(200);
            quantityCol.setCellValueFactory(new PropertyValueFactory<>("quantity"));

            table = new TableView<>();
            table.setItems(getUnits());
            table.getColumns().addAll(nameCol,priceCol,quantityCol);        
        }

        public ObservableList<Product> getUnits(){

            ObservableList<Product> unit = FXCollections.observableArrayList();    
            unit.add(new Product("Toilet",90.00,100));
            unit.add(new Product("Chair",200.00,200));
            unit.add(new Product("Avengers DVD",15.00,50));   
            return unit;
        }
    }

产品类别

    package TestTableView;

    public class Product {
        private String name;
        private int quantity;
        private double price;

        Product(){
            this.name = "";
            this.price = 0;
            this.quantity = 0;
        }
        Product(String Name,  double price, int quantity) {
            this.name = name;
            this.quantity = quantity;
            this.price = price;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public int getQuantity() {
            return quantity;
        }

        public void setQuantity(int quantity) {
            this.quantity = quantity;
        }

        public double getPrice() {
            return price;
        }

        public void setPrice(double price) {
            this.price = price;
        }

    }

//

  Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
        at TestTableView.TestTableView.getProductName(TestTableView.java:73)
        at TestTableView.TestTableView.lambda$createContextMenu$0(TestTableView.java:68)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
        at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
        at javafx.event.Event.fireEvent(Event.java:198)
        at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
        at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1405)
        at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.lambda$createChildren$343(ContextMenuContent.java:1358)
        at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
        at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
        at javafx.event.Event.fireEvent(Event.java:198)
        at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
        at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
        at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
        at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:380)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:294)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:416)
        at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:415)
        at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
        at com.sun.glass.ui.View.notifyMouse(View.java:937)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
        at java.lang.Thread.run(Thread.java:745)

Answer 1

正如 BadVegan 建议在循环修复问题之前添加 itemSelected.sorted()

public void getProductName(){
    itemSelected.sorted();
    for(int x = 0; x < itemSelected.size(); x++){
        name = itemSelected.get(x).getName();

        //do Something -> Name
    }    
    table.getSelectionModel().clearSelection();
}