Action listener on comboBox to display selection in textField

问题

I have a comboBox that contains selections. I am trying to apply an actionListener to display te selected string on a textField. I am not sure how to complete this and all I have read is confusing me even more.

Here is the code for the comboBox:

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 Code:

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

What I have so far on the actionListener:

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

        }

Full Code:

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());
                }
            }
        });


    }

}

回答1:

Consider adding an ItemListener to the JComboBox and checking that the ItemEvent state is ItemEvent.SELECTED. You can set the text field's text in the itemStateChanged method:

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

回答2:

You're on the right track. I'm not sure what the context is for your existing actionListener, but one way you could do it is as follows:

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
      }
   }
});

回答3:

add an ActionListener in which override the actionPerformed method, to the combo box. see my working example below

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);
    }

}

回答4:

I am trying to apply an actionListener to display te selected string on a textField

Add ActionListener on JComboBox add set the text in JTextField.

Sample code:

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());
        }
    }
});

It's worth reading How to Use Combo Boxes

Few Points:

Always try to avoid RAW type. Make it Generic Type.
Use JFrame#pack() instead of JFrame#setSize()
Never use setPreferredSize() instead use proper layout that is responsible for component size and position, if extremely needed then override JComponent#getPreferredSize().

Read more Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?

For example:

final JPanel panel = new JPanel(){

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

来源：https://stackoverflow.com/questions/24457607/action-listener-on-combobox-to-display-selection-in-textfield

标签

java

swing

combobox