英文:
Date Must not be null
问题
我想在我的应用程序中使用DateChooser。我已经安装并在我的代码中实现了所有内容，没有编译错误，但是当我尝试运行代码时，控制台显示错误消息，说"日期不能为Null"。我做错了什么？我需要首先实现一个"基础"日期吗？
kalender = new JPanel();kalender.setBackground(new Color(135, 206, 235));kalender.setBounds(0, 0, 506, 250);LayeredPane.add(kalender);kalender.setLayout(null);Termin = new Termin();SimpleDateFormat sdl = new SimpleDateFormat("dd-MM-yyyy");JDateChooser dateChooser = new JDateChooser();dateChooser.setBounds(169, 119, 70, 20);Termin.setDate(sdl.format(dateChooser.getDate())); // 错误可能在这里，因为没有这行，一切都能正常工作kalender.add(dateChooser);System.out.println(Termin);JButton btnNext3 = new JButton("Next");btnNext3.setBounds(215, 200, 70, 20);kalender.add(btnNext3);btnNext3.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {LayeredPane.moveToFront(kontakt);kalender.removeAll();}});
所以，我有一个单独的类"Termin"来定义约会的所有属性，我想将日期属性设置为用户在Date Chooser中选择的日期。
我尝试通过硬编码日期属性来设置日期，但是当用户使用Date Chooser进行选择时，它不会更改。
英文:
I want to use the DateChooser in my application. I have already installed and implemented everything in my code and there are no compilation errors, but when I try to run the code the console shows an error that, "Date Must not be Null". What am I doing wrong? Do I have to implement a "base" date first?
kalender = new JPanel();kalender.setBackground(new Color(135, 206, 235));kalender.setBounds(0, 0, 506, 250);LayeredPane.add(kalender);kalender.setLayout(null);Termin = new Termin();SimpleDateFormat sdl = new SimpleDateFormat("dd-MM-yyyy");JDateChooser dateChooser = new JDateChooser();dateChooser.setBounds(169, 119, 70, 20);Termin.setDate(sdl.format(dateChooser.getDate())); // the erro must be here because with out thiskalender.add(dateChooser); //line everything worksSystem.out.println(Termin);JButton btnNext3 = new JButton("Next");btnNext3.setBounds(215, 200, 70, 20);kalender.add(btnNext3);btnNext3.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {LayeredPane.moveToFront(kontakt);kalender.removeAll();}});
So I have a separate Class "Termin" to define all the attributes of an appointment, and I want to set the attributes date to whatever the user chooses in the Date Chooser.
I have tried to set the date in the attribute by hard coding it, but then it would not change when the user makes a selection with the date chooser.
答案1
得分: 2
在这行代码中：
Termin.setDate(sdl.format(dateChooser.getDate()));
因为尚未选择日期，dateChooser.getDate() 返回 null。您需要检测用户何时更改了日期。您可以使用以下代码，就像这个 Stack Overflow 页面中所示：https://stackoverflow.com/questions/4156305/is-it-possible-to-detect-a-date-change-on-a-jcalendar-jdatechooser-field
代码应该类似于：
dateChooser.getDateEditor().addPropertyChangeListener(new PropertyChangeListener() {@Overridepublic void propertyChange(PropertyChangeEvent e) {if ("date".equals(e.getPropertyName())) {java.util.Date date = (java.util.Date)e.getNewValue();Termin.setDate(sdl.format(date));}}});
英文:
In this line:
Termin.setDate(sdl.format(dateChooser.getDate()));
dateChooser.getDate() returns null because because no date has yet been selected. You need to detect when user has changed the date. You should use code as in this SO: https://stackoverflow.com/questions/4156305/is-it-possible-to-detect-a-date-change-on-a-jcalendar-jdatechooser-field
It should look something like:
dateChooser.getDateEditor().addPropertyChangeListener(new PropertyChangeListener() {@Overridepublic void propertyChange(PropertyChangeEvent e) {if ("date".equals(e.getPropertyName())) {java.util.Date date = (java.util.Date)e.getNewValue();Termin.setDate(sdl.format(date));}}});
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论