在comboBox上的操作侦听器以在textField中显示选择

Question

我有一个包含选择的comboBox。 我正在尝试应用actionListener在textField上显示选定的字符串。 我不确定如何完成此操作，而且我读过的所有内容进一步使我感到困惑。

这是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，我对actionListener的了解：

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

考虑将ItemListener添加到JComboBox并检查ItemEvent状态为ItemEvent.SELECTED 。 您可以在itemStateChanged方法中设置文本字段的文本：

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

Answer 2

您走在正确的轨道上。 我不确定您现有的actionListener的上下文是什么，但是可以使用的一种方法如下：

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在textField上显示选定的字符串

在JComboBox上添加ActionListener ，在JTextField添加设置文本。

样例代码：

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());
        }
    }
});

---

值得阅读如何使用组合框

几点：

• 始终尝试避免使用RAW类型。 使其成为通用类型 。
• 使用JFrame#pack()代替JFrame#setSize()

• 切勿使用setPreferredSize()而应使用负责组件大小和位置的正确布局，如果非常需要，请重写JComponent＃getPreferredSize（） 。

  阅读更多我应该避免在Java Swing中使用set（Preferred | Maximum | Minimum）Size方法吗？

例如：

final JPanel panel = new JPanel(){

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

Answer 4

向组合框中添加一个其中重写了actionPerformed方法的ActionListener 。 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);
    }

}