学习事件处理

Question

所以我在大学里学了一点java，并展望未来，因为我们不是在这方面，但我试图通过查看未来的考题等来自学事件处理和gui，到目前为止，我已经掌握了gui的相当方便，但事件处理还不是很多……我已经在这方面做了一段时间了，我似乎根本不能理解它们，我试图得到当按钮被按下时，它会将JTextField的length()返回到JLabel中，任何帮助都会非常感谢。谢谢

   import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
    import javax.swing.event.*;

public class guiWithCatchBlock extends JFrame implements ActionListener, MouseListener {


guiWithCatchBlock() {

    super("Attempting Event Handling");

    Container c = getContentPane();
    JButton stringLengthButton = new JButton("Get String Length");
    JTextField inputField = new JTextField();
    JLabel outputLabel = new JLabel("String Length = ");
    stringLengthButton.addActionListener(this);
    inputField.addActionListener(this);
    outputLabel.addMouseListener(this);
    c.add(stringLengthButton,BorderLayout.NORTH);
    c.add(inputField,BorderLayout.CENTER);
    c.add(outputLabel,BorderLayout.SOUTH);
    setSize(400, 300);
    show();

}

public static void main(String args[]) {

    guiWithCatchBlock testAction = new guiWithCatchBlock();

}

public void actionPerformed(ActionEvent e) {

    System.out.print(paramString());

}

@Override
public void mouseClicked(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseEntered(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseExited(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mousePressed(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseReleased(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

}

Answer 1

您需要将ActionListener传递给按钮

stringLengthButton.addActionListener(this);

您可以在实现ActionListener类时使用它。现在将触发的事件是：

public void actionPerformed(ActionEvent e) {
    // Do GUI manipulations
    System.out.print(paramString());
}

Answer 2

如果你试图在你的构造函数中声明你的inputField和outputLabel，那么以后就很难引用了，最好把它声明为类成员。

在actionPerform中，尝试获取文本长度并重新标注，如下所示

@Override
public void actionPerformed(ActionEvent e) {
    outputLabel.setText("String Length = " + inputField.getText().length());
}

完成的代码为

public class guiWithCatchBlock extends JFrame implements ActionListener, MouseListener {
    JTextField inputField;
    JLabel outputLabel;
    guiWithCatchBlock () {
        super("Attempting Event Handling");
        Container c = getContentPane();
        JButton stringLengthButton = new JButton("Get String Length");
        inputField = new JTextField();
        outputLabel = new JLabel("String Length = ");
        stringLengthButton.addActionListener(this);
        inputField.addActionListener(this);
        outputLabel.addMouseListener(this);
        c.add(stringLengthButton, BorderLayout.NORTH);
        c.add(inputField, BorderLayout.CENTER);
        c.add(outputLabel, BorderLayout.SOUTH);
        setSize(400, 300);
        show();

    }

    public static void main(String args[]) {
        guiWithCatchBlock testAction = new guiWithCatchBlock ();
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        outputLabel.setText("String Length = " + inputField.getText().length());
    }

    @Override
    public void mouseClicked(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseEntered(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseExited(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mousePressed(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseReleased(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }
}