动作听众无法正常工作？

时间：2013-10-15 13:13:29

标签： java swing awt jbutton actionlistener

我想知道你是否可以告诉我我的动作听众在哪里出错了？我将发布下面的代码和错误，它一直让我疯狂...... 

btnEdit.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                EditItem editFrame = new EditItem(sc, orderTextField, numofItemsField, totalCostField);

            }
        });

package Assesment;

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class EditItem {

    private ShoppingCart sc;
    private JTextArea orderTextField;
    private JTextField numItemsField;
    private JTextField totalCostField;
    private JTextField orderNumberJTextField;
    private JButton buttonEdit;

    private JComboBox comOrderNumber;
    private JTextField txtFieldName;
    private JTextField txtFieldQuantity;
    private JTextField txtFieldPrice ;

    public EditItem(ShoppingCart sc, JTextArea orderTextField,

        JTextField numItemsField, JTextField totalCostField) {
        this.sc = sc;
        this.orderTextField = orderTextField;
        this.numItemsField = numItemsField;
        this.totalCostField = totalCostField;

        build();
        addActionListeners();
    }

    private void build() {
        // creates a main frame called editMainFrame1
        JFrame editMainFrame1 = new JFrame("Edit");
        editMainFrame1.setVisible(true);
        editMainFrame1.setLayout(new GridLayout(5, 1));
        editMainFrame1.setResizable(false);
        editMainFrame1.setSize(300, 300);

        JPanel orderNumberPanel = new JPanel(new GridLayout(1, 2));
        JPanel nameNumberPanel = new JPanel(new GridLayout(1, 2));
        JPanel quantityNumberPanel = new JPanel(new GridLayout(1, 2));
        JPanel priceNumberPanel = new JPanel(new GridLayout(1, 2));
        JPanel buttonNumberPanel = new JPanel(new GridLayout(1, 1));

        JLabel entOrderNumber = new JLabel("Select Order Number");

        Integer[] orderNumbersList = sc.getOrderNumbersList();
        JComboBox comOrderNumber = new JComboBox(orderNumbersList);

        orderNumberPanel.add(entOrderNumber);
        orderNumberPanel.add(comOrderNumber);

        JLabel entName = new JLabel("Enter New Name");
        JTextField txtFieldName = new JTextField();
        txtFieldName.setSize(20, 20);
        nameNumberPanel.add(entName);
        nameNumberPanel.add(txtFieldName);

        JLabel entQuantity = new JLabel("Enter New Quantity");
        JTextField txtFieldQuantity = new JTextField();
        txtFieldQuantity.setSize(20, 20);
        quantityNumberPanel.add(entQuantity);
        quantityNumberPanel.add(txtFieldQuantity);

        JLabel entPrice = new JLabel("Enter New Price");
        JTextField txtFieldPrice = new JTextField();
        txtFieldPrice.setSize(20, 20);
        priceNumberPanel.add(entPrice);
        priceNumberPanel.add(txtFieldPrice);

        JButton buttonEdit = new JButton("Edit!");
        buttonNumberPanel.add(buttonEdit);

        // adding components to separate panels

        editMainFrame1.add(orderNumberPanel);
        editMainFrame1.add(nameNumberPanel);
        editMainFrame1.add(quantityNumberPanel);
        editMainFrame1.add(priceNumberPanel);
        editMainFrame1.add(buttonNumberPanel);
    }

    private void addActionListeners() {
        buttonEdit.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {

                OrderItem x = sc.findItem(Integer.parseInt((String) comOrderNumber.getSelectedItem())) ;
                sc.removeItem(x);

                String newNameEntered = txtFieldName.getText();

                int newQuantityEntered = Integer.parseInt((String) txtFieldQuantity.getText());

                double newPriceEntered = Double.parseDouble((String) txtFieldPrice.getText());

                int z = Integer.parseInt((String) comOrderNumber.getSelectedItem()) ;

                System.out.println(""+newQuantityEntered+newNameEntered);


                sc.addItem(z,newNameEntered,newQuantityEntered,newPriceEntered);

                orderTextField.setText("3" + sc.getBasketContents());
                numItemsField.setText(""+sc.getSize());
                totalCostField.setText(""+sc.getTotalPrice());




            }
        });
    }
}

Lines giving the errors :       buttonEdit.addActionListener(new ActionListener() {
Line 95
        addActionListeners(); Line 39
                EditItem editFrame = new EditItem(sc, orderTextField, numofItemsField, totalCostField);
Line 252.

我一直在下面的错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Assesment.EditItem.addActionListeners(EditItem.java:95)
    at Assesment.EditItem.<init>(EditItem.java:39)
    at Assesment.Store$3.actionPerformed(Store.java:252)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
    at java.awt.Component.processMouseEvent(Component.java:6382)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
    at java.awt.Component.processEvent(Component.java:6147)
    at java.awt.Container.processEvent(Container.java:2083)
    at java.awt.Component.dispatchEventImpl(Component.java:4744)
    at java.awt.Container.dispatchEventImpl(Container.java:2141)
    at java.awt.Component.dispatchEvent(Component.java:4572)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210)
    at java.awt.Container.dispatchEventImpl(Container.java:2127)
    at java.awt.Window.dispatchEventImpl(Window.java:2489)
    at java.awt.Component.dispatchEvent(Component.java:4572)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:710)
    at java.awt.EventQueue.access$400(EventQueue.java:82)
    at java.awt.EventQueue$2.run(EventQueue.java:669)
    at java.awt.EventQueue$2.run(EventQueue.java:667)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
    at java.awt.EventQueue$3.run(EventQueue.java:683)
    at java.awt.EventQueue$3.run(EventQueue.java:681)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:680)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

它正在驱使我疯狂，因为我有其他行动Listerners似乎以同样的方式工作，而不是给我任何错误

3 个答案:

答案 0 :(得分：1)

    JButton buttonEdit = new JButton("Edit!");

应该是：

    buttonEdit = new JButton("Edit!");

通过添加JButton前缀，它实际上变成了一个局部变量，“隐藏”真实的前缀，它总是null。

答案 1 :(得分：1)

使用build()方法

JButton buttonEdit = new JButton("Edit!");

不应该

buttonEdit = new JButton("Edit!");

初始化私有字段？

答案 2 :(得分：0)

 buttonEdit.addActionListener(new ActionListener() {

buttonEdit为null，因此您无法使用任何方法为null。看看这张图片（在Eclipse中调试）： https://dl.dropboxusercontent.com/u/1987930/screenshot.png Why?

为什么？

 JButton buttonEdit = new JButton("Edit!"); //You set a local varaiable, not to class, so
// remove first word
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