Question

我有一个包含选择的组合框。我正在尝试应用actionListener来在textField上显示选定的字符串。我不知道如何完成这一点，我读过的所有内容都让我更加困惑。

以下是comboBox的代码：

JComboBox comboBox = new JComboBox();
        comboBox.setModel(new DefaultComboBoxModel(new String[] {"Select Something", "Selection 1", "Selection 2", "Selection 3", "Selection 4"}));
        panelTop.add(comboBox);
        comboBox.setPreferredSize(new Dimension(160, 20));
        comboBox.addItem("Select Something");

textField代码：

textField = new JTextField();
        panelTop.add(textField);
        textField.setColumns(40);

到目前为止我在actionListener上的内容：

public void actionPerformed(ActionEvent e) {
            JComboBox comboBox = (JComboBox)e.getSource();
            String newSelection = (String)comboBox.getSelectedItem();
            currentPattern = newSelection;

        }

完整代码：

package SwingAssign2;

import java.awt.Dimension;
import java.awt.EventQueue;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;

import java.awt.BorderLayout;

import javax.swing.JComboBox;
import javax.swing.JTextField;

import java.awt.FlowLayout;

import javax.swing.SwingConstants;

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

import javax.swing.DefaultComboBoxModel;

public class SwingAssign2 {

    private JFrame frame;
    private JTextField textField;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    SwingAssign2 window = new SwingAssign2();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public SwingAssign2() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setSize(600, 500);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panelTop = new JPanel();
        FlowLayout fl_panelTop = (FlowLayout) panelTop.getLayout();
        fl_panelTop.setAlignment(FlowLayout.LEFT);
        frame.getContentPane().add(panelTop, BorderLayout.NORTH);
        //panel.setLayout(new FlowLayout(FlowLayout.LEFT, 5, 5));

        final JComboBox comboBox = new JComboBox();
        comboBox.setModel(new DefaultComboBoxModel(new String[] {"Select Something", "Selection 1", "Selection 2", "Selection 3", "Selection 4"}));
        panelTop.add(comboBox);
        comboBox.setPreferredSize(new Dimension(160, 20));
        comboBox.addItem("Select Something");


        textField = new JTextField();
        panelTop.add(textField);
        textField.setColumns(40);

        JPanel panelBottom = new JPanel();
        frame.getContentPane().add(panelBottom, BorderLayout.SOUTH);
        panelBottom.setLayout(new BorderLayout(0, 0));

        JLabel status = new JLabel("Status");
        status.setHorizontalAlignment(SwingConstants.CENTER);
        panelBottom.add(status, BorderLayout.SOUTH);
        status.setBorder(BorderFactory.createLoweredBevelBorder());

        JTextPane txtpnSomeContentOn_B = new JTextPane();
        txtpnSomeContentOn_B.setText("Some content on the bottom panel\r\nMore content\r\nSome more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content");
        JScrollPane jScrollPane3 = new JScrollPane(txtpnSomeContentOn_B);
        jScrollPane3.setHorizontalScrollBarPolicy(
                JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        jScrollPane3.setVerticalScrollBarPolicy(
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        panelBottom.add(jScrollPane3, BorderLayout.NORTH);
        jScrollPane3.setPreferredSize(new Dimension(200, 200));
        //bText.setBorder(BorderFactory.createLoweredBevelBorder());

        JPanel panelCenter = new JPanel();
        frame.getContentPane().add(panelCenter, BorderLayout.CENTER);
        panelCenter.setLayout(new GridLayout(0, 2, 0, 0));

        JTextPane txtpnSomeContentOn_0 = new JTextPane();
        txtpnSomeContentOn_0.setText("Some content on the left panel\r\nMore content\r\nSome more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content");
        JScrollPane jScrollPane1 = new JScrollPane(txtpnSomeContentOn_0);
        jScrollPane1.setHorizontalScrollBarPolicy(
                JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        jScrollPane1.setVerticalScrollBarPolicy(
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        panelCenter.add(jScrollPane1);

        JTextPane txtpnSomeContentOn = new JTextPane();
        txtpnSomeContentOn.setText("Some content on the right panel\r\nMore content\r\nSome more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content\r\nMore and more content");
        JScrollPane jScrollPane2 = new JScrollPane(txtpnSomeContentOn);
        jScrollPane2.setHorizontalScrollBarPolicy(
                JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        jScrollPane2.setVerticalScrollBarPolicy(
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        panelCenter.add(jScrollPane2);

        comboBox.addItemListener(new ItemListener() {
            @Override
            public void itemStateChanged(ItemEvent e) {
                if(e.getStateChange() == ItemEvent.SELECTED) {
                    textField.setText((String) comboBox.getSelectedItem());
                }
            }
        });


    }

}

Answer 1

考虑向ItemListener添加JComboBox并检查ItemEvent州是否为ItemEvent.SELECTED。您可以在itemStateChanged方法中设置文字字段的文字：

comboBox.addItemListener(new ItemListener() {
    @Override
    public void itemStateChanged(ItemEvent e) {
        if(e.getStateChange() == ItemEvent.SELECTED) {
            textField.setText((String) comboBox.getSelectedItem());
        }
    }
});

Answer 2

你走在正确的轨道上。我不确定你现有的actionListener的上下文是什么，但你可以这样做的一种方法如下：

comboBox.addItemListener(new ItemListener() {
   @Override
   public void itemStateChanged(ItemEvent arg0) { // picks up changes to combobox selection
      if (arg0.getStateChange() == ItemEvent.SELECTED) {
         String newSelection = comboBox.getSelectedItem(); // takes the selected item
         textField.setText(newSelection); // publishes to the textfield
      }
   }
});

Answer 3

我正在尝试应用actionListener来在textField上显示选定的字符串

在ActionListener上添加JComboBox添加JTextField中的文字。

示例代码：

final JTextField jTextField = new JTextField();

final JComboBox<String> comboBox = new JComboBox<String>();
comboBox.setModel(new DefaultComboBoxModel<String>(new String[] { 
    "Select Something", "Selection 1", "Selection 2",   
    "Selection 3", "Selection 4" }));

// set first one selected
comboBox.setSelectedIndex(0);

comboBox.addActionListener(new ActionListener() {

    @Override
    public void actionPerformed(ActionEvent ae) {
        // check whether there is any selection
        if(comboBox.getSelectedIndex()!=-1){
            jTextField.setText(comboBox.getSelectedItem().toString());
        }
    }
});

值得一读How to Use Combo Boxes

几点：

始终尽量避免使用RAW类型。设为Generic Type。
使用JFrame#pack()代替JFrame#setSize()
永远不要使用setPreferredSize()而是使用负责组件大小和位置的正确布局，如果非常需要，则覆盖JComponent#getPreferredSize()。

了解更多Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?

例如：

final JPanel panel = new JPanel(){

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(...,...);
    }
};

Answer 4

将覆盖ActionListener方法的actionPerformed添加到组合框中。请参阅下面的工作示例

import java.awt.EventQueue;
import java.util.Vector;

import javax.swing.DefaultComboBoxModel;
import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.EmptyBorder;
import javax.swing.JComboBox;

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

public class JTextFieldTest extends JFrame {

    private JPanel contentPane;
    private JTextField textField;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    JTextFieldTest frame = new JTextFieldTest();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public JTextFieldTest() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 298, 220);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);

        Vector<String> comboBoxItems=new Vector();
        comboBoxItems.add("A");
        comboBoxItems.add("B");
        comboBoxItems.add("C");
        final DefaultComboBoxModel model = new DefaultComboBoxModel(comboBoxItems);
        final JComboBox comboBox = new JComboBox(model);
        comboBox.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {//here your actionPerformed method
                textField.setText((String) comboBox.getSelectedItem());
            }
        });

        textField = new JTextField();
        textField.setColumns(10);
        GroupLayout gl_contentPane = new GroupLayout(contentPane);
        gl_contentPane.setHorizontalGroup(
            gl_contentPane.createParallelGroup(Alignment.LEADING)
                .addGroup(gl_contentPane.createSequentialGroup()
                    .addGroup(gl_contentPane.createParallelGroup(Alignment.LEADING)
                        .addGroup(gl_contentPane.createSequentialGroup()
                            .addGap(110)
                            .addComponent(comboBox, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE))
                        .addGroup(gl_contentPane.createSequentialGroup()
                            .addGap(83)
                            .addComponent(textField, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)))
                    .addContainerGap(103, Short.MAX_VALUE))
        );
        gl_contentPane.setVerticalGroup(
            gl_contentPane.createParallelGroup(Alignment.LEADING)
                .addGroup(gl_contentPane.createSequentialGroup()
                    .addGap(37)
                    .addComponent(comboBox, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                    .addGap(18)
                    .addComponent(textField, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                    .addContainerGap(76, Short.MAX_VALUE))
        );
        contentPane.setLayout(gl_contentPane);
    }

}

comboBox上的动作侦听器，用于在textField中显示选择

4 个答案:

几点：