Question

我希望在点击我的节目按钮时看到标签，但是不起作用！

public class d4 extends JFrame implements ActionListener {

Connection con;
String dbName = "mydb";
String bdUser = "root";
String dbPassword = "2323";
String dbUrl = "jdbc:mysql://localhost/mydb";
JButton showButton;
static JLabel[] lbl;
JPanel panel;

public d4() {

try {
    con = DriverManager.getConnection(dbUrl, bdUser, dbPassword);
    System.out.println("Connected to database successfully!");

} catch (SQLException ex) {
    System.out.println("Could not connect to database");
}

add(mypanel(), BorderLayout.PAGE_START);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(400, 500);
setLocation(300, 30);
setVisible(true);
pack();
}

public JPanel mypanel() {
panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
showButton = new JButton("Show");
showButton.addActionListener(this);
panel.add(showButton);
revalidate();
repaint();

return panel;
}

@Override
public void actionPerformed(ActionEvent e) {
if (e.getSource() == showButton) {
            lbl = recordsLabel();
        for(JLabel jlabel : lbl){
            panel.add(jlabel);  
}
}
public JLabel[] recordsLabel() {
try {
    Statement st1 = con.createStatement();
    ResultSet result1 = st1.executeQuery("select * from mytable");
    ArrayList<String> lableList = new ArrayList<>();
    while (result1.next()) {
        String resultRow = result1.getString(1) + " " + result1.getString(2);
        System.out.println(resultRow);
        lableList.add(resultRow);
    }
    Object[] arrayResultRow = lableList.toArray();

    int rows = result1.last() ? result1.getRow() : 0;

    lbl = new JLabel[rows];
    for (int i = 0; i < rows; i++) {
        lbl[i] = new JLabel(arrayResultRow[i].toString());
    }

} catch (SQLException sqle) {
    System.out.println("Can not excute sql statement");
}
return lbl;
}

public static void main(String[] args) {
new d4();
}
}

Answer 1

您尚未实现ActionListener接口

编辑：您的更新代码显示您有。现在正如Hovercraft Full Of Eels建议的那样，下一步是用调试技术来解决问题。

Answer 2

在向面板添加标签后尝试调用revalidate()和repaint()，您还需要在框架上调用pack()以调整框架大小以适应新组件。

Answer 3

您正在调用myPanel() 两次，并且通过这样做，您将JLabel添加到从未添加到GUI的JPanel。

解决方案：不要这样做。你的myPanel()开头很麻烦，因为它返回一个JPanel并同时设置了类字段面板。因此，设置一次面板变量，然后使用变量。

是的，revalidate()和repaint()根据Azad的建议（1+给他）添加组件后的容器。

单击按钮时JLabel不显示

3 个答案: