如何通过 Combobox 在 java 中设置框架的标题？

Question

我想创建如下图所示的内容，当用户从 Combobox 选项中选择年、月和日时，这些操作将更改标题，并且必须根据所选数据进行更改，这很简单，我还是新手

到目前为止，我已经做到了，问题是它不起作用，我该怎么做？请你帮帮我吗？

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.JOptionPane;
import javax.swing.JTextField;


public class DateForm_Complete extends JFrame {

    private JLabel          year, month, day;
    private JComboBox       cmonth, cday, cyear;

    public DateForm_Complete() {

        setTitle("Date Selection");
        setSize(400,100);
        setupWidgets();
        setVisible(true);
    }

    private void setupWidgets() {
        year=   new JLabel("Year");
        month=  new JLabel("Month");
        day=    new JLabel("Day");
        cyear=  new JComboBox();
        cmonth= new JComboBox();
        cday=   new JComboBox();

        setLayout(new GridLayout (2,3));

        add(year);   add(month);    add(day);
        add(cyear);  add(cmonth);   add(cday);

        for (int i=1900; i<2019; i++)   
        {
            cyear.addItem(i);
        }

        String months[] = {"January","February","March","April","May","June","July","August","September","October","November","December"};

        for (int i=0; i<12; i++)
        {
            cmonth.addItem(months[i]);
        }

        for (int i=1; i<32; i++)    
        {
            cday.addItem(i);
        }
        setupEvents();
    }

    private void setupEvents() {

        setDefaultCloseOperation(EXIT_ON_CLOSE);

        cyear.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent ev) {
                JComboBox combo = (JComboBox)ev.getSource();
                String texty = (String)combo.getSelectedItem(); 
            }
        });

        cmonth.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent ev) {
                JComboBox combo = (JComboBox)ev.getSource();
                String textm = (String)combo.getSelectedItem();
            }
        });

        cday.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent ev) {
                JComboBox combo = (JComboBox)ev.getSource();
                String textd = (String)combo.getSelectedItem();     
            }
        });
        setTitle("Today is "+ texd+ "of "+ textm + "of " +texty);               
    }   
    public static void main(String[] args) {

        new DateForm_Complete();        
    }
}

Answer 1

Whenever an item in a combo box is selected you need to reset the entire string you want to display as the title.

所以，你需要一个方法在你的类中，比如：

public void changeTitle()
{
    String year = cyear.getSeletedItem().toString();
    String month = cmonth.getSelectedItem().toString();
    String day = cday.getSelectedItem().toString();

    setTitle("Today is "+ day + "of "+ month + "of " + year);      
}

然后从 3 个 ActionListener 中调用 changTitle() 方法。`

Answer 2

我在您的代码中修复了一些问题，现在它可以工作了。试试看。主要变化是：

在代码中的setTitle("Today is "+ texd+ "of "+ textm + "of " +texty); 中，变量textd、textm 和texty 超出范围（意味着它们在每个actionPerformed() 方法中声明。因此它们在@987654326 之外不可用/可见@ 方法。）。所以我将它们设为DateForm_Complete 类的实例变量。

然后我从每个actionPerformed() 方法调用setTitle("Today is "+ textd+ " of "+ textm + " of " +texty);。因为我猜您的要求是在每个组合框值更改后立即更新标题。

texd 变量名也有错别字。

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

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class DateForm_Complete extends JFrame {

  private JLabel          year, month, day;
  private JComboBox       cmonth, cday, cyear;

  private String texty = "1900";
  private String textm = "January";
  private String textd = "1";

  public DateForm_Complete() {

    setTitle("Date Selection");
    setSize(400,100);
    setupWidgets();
    setVisible(true);
  }

  private void setupWidgets() {
    year=   new JLabel("Year");
    month=  new JLabel("Month");
    day=    new JLabel("Day");
    cyear=  new JComboBox();
    cmonth= new JComboBox();
    cday=   new JComboBox();

    setLayout(new GridLayout (2,3));

    add(year);   add(month);    add(day);
    add(cyear);  add(cmonth);   add(cday);

    for (int i=1900; i<2019; i++)
    {
      cyear.addItem(i);
    }

    String months[] = {"January","February","March","April","May","June","July","August","September","October","November","December"};

    for (int i=0; i<12; i++)
    {
      cmonth.addItem(months[i]);
    }

    for (int i=1; i<32; i++)
    {
      cday.addItem(i);
    }
    setupEvents();
  }

  private void setupEvents() {

    setDefaultCloseOperation(EXIT_ON_CLOSE);

    cyear.addActionListener(new ActionListener() {

      @Override
      public void actionPerformed(ActionEvent ev) {
        JComboBox combo = (JComboBox)ev.getSource();
        texty = combo.getSelectedItem().toString();
        setTitle("Today is "+ textd+ " of "+ textm + " of " +texty);
      }
    });

    cmonth.addActionListener(new ActionListener() {

      @Override
      public void actionPerformed(ActionEvent ev) {
        JComboBox combo = (JComboBox)ev.getSource();
        textm = (String)combo.getSelectedItem();
        setTitle("Today is "+ textd+ " of "+ textm + " of " +texty);
      }
    });

    cday.addActionListener(new ActionListener() {

      @Override
      public void actionPerformed(ActionEvent ev) {
        JComboBox combo = (JComboBox)ev.getSource();
        textd = combo.getSelectedItem().toString();
        setTitle("Today is "+ textd+ " of "+ textm + " of " +texty);
      }
    });

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

    new DateForm_Complete();
  }
}