即使在以编程方式设置日期时分离侦听器，JDateChooser 上的 propertychangelistener 也会额外触发 2 次

Question

我正在为我正在开发的 java swing 项目使用 JDateChooser，在这个项目中，日期可以通过两种方式设置：由最终用户或以编程方式设置。

所以我在相应的 class 中定义了一个属性changelistener（变量 trig 被初始化为零并跟踪属性的次数改变被倾听）。

public class WriteEntry{
private int trig=0;
private Date currentDate = new Date();
public JDateChooser dateChooser = new JDateChooser();
public CustomDate selectedDate = DateConverter.convertDate(currentDate);
private static String filename = StorageSpace.currentpath+CurrentUser.getInstance().getUserName()+"\"+
        Integer.toString(selectedDate.getYear())+"\"
          +Integer.toString(selectedDate.getMonth())+"\"+Integer.toString(selectedDate.getDay())+".txt";
private JLabel dayinfo = new JLabel("");
private JTextArea contentfield = new JTextArea("");
private PropertyChangeListener lis = new PropertyChangeListener(){
      @Override
      public void propertyChange(PropertyChangeEvent e) {
          System.out.println("triggered "+trig++);
            if(dateBoundary())  {
                selectedDate = DateConverter.convertDate(dateChooser);
                filename = StorageSpace.currentpath+CurrentUser.getInstance().getUserName()+"\"+
                        Integer.toString(selectedDate.getYear())+"\"
                          +Integer.toString(selectedDate.getMonth())+"\"+Integer.toString(selectedDate.getDay())+".txt";
            }
            else {
                updateDateChooser(selectedDate);
            }
            if(isAlreadyWritten())
            {
                try {
                    updateEditFields(selectedDate, "content");
                } catch (IOException e1) {
                    e1.printStackTrace();
                }   
            }
            else
            {       
                contentfield.setText("Start writing here");
                dayinfo.setText("You are making entry for: "+ new SimpleDateFormat("dd/MM/yyyy").format(dateChooser.getDate()));        
            }
      }      
    };
WriteEntry() //constructor
{
dateChooser.setDateFormatString("dd MM yyyy");
dateChooser.addPropertyChangeListener(lis);
updateEditFields(DateConverter.convertDate(currentDate), "Start");
}
}

这里是 dateBoundary() 的代码：

public static boolean dateBoundary() {
    Object[] option = {"I get it","My Bad!"};
    if(dateChooser.getDate().compareTo(currentDate)>0) {
        JOptionPane.showOptionDialog(HomePage.getFrame(),"message1",
                "",JOptionPane.DEFAULT_OPTION,JOptionPane.ERROR_MESSAGE,null,option,option[0]);
        return false;
    }
    if(dateChooser.getDate().compareTo(DateConverter.convertfromCustom(CurrentUser.getInstance().getDob()))<0){
JOptionPane.showOptionDialog(HomePage.getFrame(),"message2",
                "",JOptionPane.DEFAULT_OPTION,JOptionPane.ERROR_MESSAGE,null,option,option[0]);
        return false;
    }
    return true;
}

isAlreadyWritten() 的代码：

public static boolean isAlreadyWritten() {
    File f = new File(filename);
    if(f.length()!=0)
    {
        Object[] option = {"Read","Edit"};
        JOptionPane.showOptionDialog(HomePage.getFrame(),"You already updated diary for this day. Do you want to edit?",
                "",JOptionPane.DEFAULT_OPTION,JOptionPane.INFORMATION_MESSAGE,null,option,option[0]);
        return true;
    }
    else
        return false;
}

updateDateChooser() 代码：

public static void updateDateChooser(CustomDate date) {
dateChooser.removePropertyChangeListener(lis); //to stop it from getting triggered when date is set programatically
dateChooser.setDate(DateConverter.convertfromCustom(date));
dateChooser.addPropertyChangeListener(lis);
}

updateEditFields() 代码：

public static void updateEditFields(CustomDate searchDate, String excontent) {
updateDateChooser(searchDate);
selectedDate = DateConverter.convertDate(dateChooser);
dayinfo.setText("You are editing entry for: "+ new SimpleDateFormat("dd/MM/yyyy").format(dateChooser.getDate()));
contentfield.setText(excontent);

}

现在我的日期边界函数可以正常工作了。 whenever a date greater than current date is chosen, the optiondialog gets displayed and its gone after a click, and the datechooser is set to the last selected date, although the 属性change method is called thrice:

在显示对话框之前一次
对话框关闭后两次。

但是我的 isAlreadyWritten() 没有按预期工作，选项对话框显示了 4 次，属性change() 方法被调用了四次：每次显示对话框前一次。

我想了解为什么在以编程方式设置日期时，即使日期选择器与侦听器分离，为什么属性change 仍被调用 4 次？

Answer 1

所以，我把这个简短的片段放在一起运行它

import com.toedter.calendar.JDateChooser;
import java.awt.EventQueue;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.Date;
import javax.swing.JFrame;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

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

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }
                JDateChooser dateChooser = new JDateChooser();
                dateChooser.addPropertyChangeListener(new PropertyChangeListener() {
                    @Override
                    public void propertyChange(PropertyChangeEvent evt) {
                        System.out.println(evt.getPropertyName());
                    }
                });
                dateChooser.setDate(new Date());

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(dateChooser);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

}

我打开日期选择器并选择了一个日期。程序输出...

date
ancestor
date
date

我是以编程方式设置日期的吗
ancestor 是否添加到容器中
我在选择日期选择器吗
我在选择日期吗

因此，如您所见，您不仅收到了大量 "date" 属性更改的垃圾邮件，而且还收到了所有 "other" 属性也有变化

所以，您要做的第一件事就是将通知限制为 "date" 属性，例如...

dateChooser.addPropertyChangeListener("date", new PropertyChangeListener() {
    @Override
    public void propertyChange(PropertyChangeEvent evt) {
        System.out.println(evt.getPropertyName());
    }
});

这至少意味着您不会被您不关心的所有其他信息所打扰。

虽然您可以添加和删除侦听器，但我觉得这很麻烦，因为我并不总是有对侦听器的引用，相反，我倾向于使用状态标志

private boolean manualDate = false;
//...
dateChooser.addPropertyChangeListener("date", new PropertyChangeListener() {
    @Override
    public void propertyChange(PropertyChangeEvent evt) {
        if (manualDate) {
            return;
        }
        System.out.println(evt.getPropertyName());
    }
});

manualDate = true;
dateChooser.setDate(new Date());
manualDate = false;

变化不大，但仅此一项就意味着您现在只有两个事件通知。

相反，您应该将 oldValue 与 PropertyChangeEvent

的 newValue 进行比较

JDateChooser dateChooser = new JDateChooser();
dateChooser.addPropertyChangeListener("date", new PropertyChangeListener() {
    @Override
    public void propertyChange(PropertyChangeEvent evt) {
        if (manualDate) {
            return;
        }
        Date newDate = (Date) evt.getNewValue();
        Date oldDate = (Date) evt.getOldValue();
        if (newDate != null && oldDate != null) {
            LocalDate newLD = LocalDate.ofInstant(newDate.toInstant(), ZoneId.systemDefault());
            LocalDate oldLD = LocalDate.ofInstant(oldDate.toInstant(), ZoneId.systemDefault());
            if (newLD.equals(oldLD)) {
                return;
            }
        }
        System.out.println(evt.getPropertyName());
    }
});

现在，我们只剩下一个更改事件了。唯一的缺点是当他们重新选择当前日期时它不会告诉你。

稍微好一点的工作流程可能是完全忽略它，只需要一个 JButton，用户可以按下它来执行您需要执行的任何相关操作

可运行示例...

import com.toedter.calendar.JDateChooser;
import java.awt.EventQueue;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.time.LocalDate;
import java.time.ZoneId;
import java.util.Date;
import javax.swing.JFrame;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

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

    private boolean manualDate;

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }
                JDateChooser dateChooser = new JDateChooser();
                dateChooser.addPropertyChangeListener("date", new PropertyChangeListener() {
                    @Override
                    public void propertyChange(PropertyChangeEvent evt) {
                        if (manualDate) {
                            return;
                        }
                        Date newDate = (Date) evt.getNewValue();
                        Date oldDate = (Date) evt.getOldValue();
                        if (newDate != null && oldDate != null) {
                            LocalDate newLD = LocalDate.ofInstant(newDate.toInstant(), ZoneId.systemDefault());
                            LocalDate oldLD = LocalDate.ofInstant(oldDate.toInstant(), ZoneId.systemDefault());
                            if (newLD.equals(oldLD)) {
                                return;
                            }
                        }
                        System.out.println(evt.getPropertyName());
                    }
                });
                manualDate = true;
                dateChooser.setDate(new Date());
                manualDate = false;

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(dateChooser);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

}

即使在以编程方式设置日期时分离侦听器，JDateChooser 上的 propertychangelistener 也会额外触发 2 次

propertychangelistener on a JDateChooser gets triggered 2 times additionally even when the listener is detached while setting the date programatically

java

swing

jdatechooser

可运行示例...