JScrollPane没有出现
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我已经查看了许多类似于此的其他线程，但没有一个修复工作。添加之后我尝试过做contentPanel.revalidate();和contentPanel.repaint();。我已经尝试将JScrollPane和JTextArea添加到contentPanel，我已经单独尝试过。我尝试过从JTextArea到JTextPane，但是没有一个工作。没有JScrollPane，JTextArea显示正常，但是当我添加它时，JTextArea完全消失了。我正在使用null布局，我认为这可能是问题，但如果有一个解决方案不涉及更改布局，我宁愿这样做。如果没有其他方法可以修改布局，请告诉我。谢谢。
下面是代码（它是一个JDialog窗口，它是主窗口的弹出窗口）`：
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.text.SimpleDateFormat;
import java.time.DateTimeException;
import java.time.LocalDateTime;
import java.time.Month;
import java.util.ArrayList;
import java.util.Calendar;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JCheckBox;
import javax.swing.JComboBox;
import javax.swing.JDialog;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.border.EmptyBorder;
public class TransactionsDialog extends JDialog
{
private static final long serialVersionUID = 6939141004692809959L;
private final JPanel contentPanel = new JPanel();
private SimpleDateFormat monthDate = new SimpleDateFormat("MMMM");
private JTextArea txtTransactions;
private JComboBox<String> comboStartMonth;
private JComboBox<Integer> comboStartDay;
private JComboBox<Integer> comboStartYear;
private JComboBox<String> comboEndMonth;
private JComboBox<Integer> comboEndDay;
private JComboBox<Integer> comboEndYear;
private JCheckBox chckbxStartDate;
private JCheckBox chckbxEndDate;
/**
* Create the dialog.
*/
public TransactionsDialog(BankAccount account)
{
setResizable(false);
/**
* Populating (Day, Month, Year) Arrays.
*/
ArrayList<String> monthList = new ArrayList<String>();
for(int month = 0; month < 12; month++)
{
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.MONTH, month);
String monthName = monthDate.format(calendar.getTime());
monthList.add(monthName);
}
ArrayList<Integer> dayList = new ArrayList<Integer>();
for(int day = 1; day <= 31; day++)
{
dayList.add(day);
}
ArrayList<Integer> yearList = new ArrayList<Integer>();
for(int year = 1980; year <= Calendar.getInstance().get(Calendar.YEAR); year++)
{
yearList.add(year);
}
setTitle("Transactions of " + account);
setBounds(100, 100, 404, 300);
getContentPane().setLayout(new BorderLayout());
contentPanel.setBorder(new EmptyBorder(5, 5, 5, 5));
getContentPane().add(contentPanel, BorderLayout.CENTER);
contentPanel.setLayout(null);
comboStartMonth = new JComboBox<String>();
comboStartMonth.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
listTransactions(account);
}
});
comboStartMonth.setModel(new DefaultComboBoxModel<String>(monthList.toArray(new String[monthList.size()])));
comboStartMonth.setEnabled(false);
comboStartMonth.setBounds(100, 8, 118, 20);
contentPanel.add(comboStartMonth);
comboStartDay = new JComboBox<Integer>();
comboStartDay.setModel(new DefaultComboBoxModel<Integer>(dayList.toArray(new Integer[dayList.size()])));
comboStartDay.setEnabled(false);
comboStartDay.setBounds(228, 8, 71, 20);
comboStartDay.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
listTransactions(account);
}
});
contentPanel.add(comboStartDay);
comboStartYear = new JComboBox<Integer>();
comboStartYear.setModel(new DefaultComboBoxModel<Integer>(yearList.toArray(new Integer[yearList.size()])));
comboStartYear.setSelectedIndex(comboStartYear.getItemCount() - 1);
comboStartYear.setEnabled(false);
comboStartYear.setBounds(309, 8, 71, 20);
comboStartYear.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
listTransactions(account);
}
});
contentPanel.add(comboStartYear);
comboEndMonth = new JComboBox<String>();
comboEndMonth.setModel(new DefaultComboBoxModel<String>(monthList.toArray(new String[monthList.size()])));
comboEndMonth.setEnabled(false);
comboEndMonth.setBounds(100, 34, 119, 20);
comboEndMonth.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
listTransactions(account);
}
});
contentPanel.add(comboEndMonth);
comboEndDay = new JComboBox<Integer>();
comboEndDay.setModel(new DefaultComboBoxModel<Integer>(dayList.toArray(new Integer[dayList.size()])));
comboEndDay.setEnabled(false);
comboEndDay.setBounds(228, 34, 71, 20);
comboEndDay.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
listTransactions(account);
}
});
contentPanel.add(comboEndDay);
comboEndYear = new JComboBox<Integer>();
comboEndYear.setModel(new DefaultComboBoxModel<Integer>(yearList.toArray(new Integer[yearList.size()])));
comboEndYear.setSelectedIndex(comboEndYear.getItemCount() - 1);
comboEndYear.setEnabled(false);
comboEndYear.setBounds(309, 34, 71, 20);
comboEndYear.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
listTransactions(account);
}
});
contentPanel.add(comboEndYear);
txtTransactions = new JTextArea();
txtTransactions.setFont(new Font("Courier New", Font.PLAIN, 11));
txtTransactions.setEditable(false);
txtTransactions.setBounds(10, 63, 368, 187);
JScrollPane txtTScrollPane = new JScrollPane(txtTransactions);
contentPanel.add(txtTScrollPane);
contentPanel.revalidate();
contentPanel.repaint();
chckbxStartDate = new JCheckBox("Start Date:");
chckbxStartDate.setBounds(6, 7, 89, 23);
chckbxStartDate.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
if(chckbxStartDate.isSelected())
{
comboStartMonth.setEnabled(true);
comboStartDay.setEnabled(true);
comboStartYear.setEnabled(true);
}
else
{
comboStartMonth.setEnabled(false);
comboStartDay.setEnabled(false);
comboStartYear.setEnabled(false);
}
listTransactions(account);
}
});
contentPanel.add(chckbxStartDate);
chckbxEndDate = new JCheckBox("End Date:");
chckbxEndDate.setBounds(6, 33, 89, 23);
chckbxEndDate.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(chckbxEndDate.isSelected())
{
comboEndMonth.setEnabled(true);
comboEndDay.setEnabled(true);
comboEndYear.setEnabled(true);
}
else
{
comboEndMonth.setEnabled(false);
comboEndDay.setEnabled(false);
comboEndYear.setEnabled(false);
}
listTransactions(account);
}
});
contentPanel.add(chckbxEndDate);
listTransactions(account);
}
private void listTransactions(BankAccount account)
{
LocalDateTime startTime;
LocalDateTime endTime;
String startMonthName = (String) comboStartMonth.getSelectedItem();
int startDay = (int) comboStartDay.getSelectedItem();
int startYear = (int) comboStartYear.getSelectedItem();
String endMonthName = (String) comboEndMonth.getSelectedItem();
int endDay = (int) comboEndDay.getSelectedItem();
int endYear = (int) comboEndYear.getSelectedItem();
if(chckbxStartDate.isSelected())
{
int startMonth = Month.valueOf(startMonthName.toUpperCase()).getValue();
try
{
startTime = LocalDateTime.of(startYear, startMonth, startDay, 0, 0);
}
catch(DateTimeException e)
{
txtTransactions.setText("INVALID DATE");
return;
}
}
else
{
startTime = null;
}
if(chckbxEndDate.isSelected())
{
int endMonth = Month.valueOf(endMonthName.toUpperCase()).getValue();
try
{
endTime = LocalDateTime.of(endYear, endMonth, endDay, 23, 59);
}
catch(DateTimeException e)
{
txtTransactions.setText("INVALID DATE");
return;
}
}
else
{
endTime = null;
}
ArrayList<Transaction> transactionList = account.getTransactions(startTime, endTime);
String output = "";
int maxAmountDigits = 1;
for(Transaction t : transactionList)
{
String stringAmount = String.format("%.2f", t.getAmount());
if(stringAmount.length() > maxAmountDigits)
maxAmountDigits = stringAmount.length();
}
output += String.format("%-10s %-8s %-" + (maxAmountDigits + 1) + "s %s
", "Date", "Time", "Amount", "Description");
//https://stackoverflow.com/questions/37791455/java-string-format-adding-spaces-to-integers
output += String.format("%0" + 100 + "d
", 0).replace("0", "-");
for(Transaction t : transactionList)
{
output += String.format("%d.%02d.%02d %02d:%02d:%02d $%-" + maxAmountDigits + ".2f %s
", t.getTransactionTime().getYear(),
t.getTransactionTime().getMonthValue(),
t.getTransactionTime().getDayOfMonth(),
t.getTransactionTime().getHour(),
t.getTransactionTime().getMinute(),
t.getTransactionTime().getSecond(),
t.getAmount(),
t.getDescription());
}
txtTransactions.setText(output);
}
}
答案
contentPanel.setLayout(null);
首先，将布局设置为null：
JScrollPane txtTScrollPane = new JScrollPane(txtTransactions);
contentPanel.add(txtTScrollPane);
//contentPanel.revalidate();
//contentPanel.repaint();
然后将滚动窗格添加到内容面板。但是，您没有在滚动窗格上使用setBounds（），并且组件的默认大小为（0,0），因此无需绘制任何内容。
但是，解决方案不是添加setBounds（...）。解决方案是不使用null布局。使用null布局看起来似乎更容易，但是当你在滚动窗格中使用时，你会遇到这样的问题并且组件无法正常工作。
所以正确的解决方案是修复你的代码并使用Layout Managers。 Swing旨在与布局管理器一起使用。然后布局管理器将设置组件的大小和位置，因此您不必担心它。
revalidate（）和repaint（）仅在将组件添加到可见GUI以调用布局管理器时使用，因此不需要它们。
此外，在创建文本区域时，请执行以下操作：
//txtTransactions = new JTextArea();
txtTransactions = new JTextArea(5, 20);
这将使文本区域根据文本区域的行/列和字体确定其自己的首选大小。然后布局管理员可以做得更好。
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