JFrame - 动作监听器

Question

我正在构建一个使用 JFrame 的程序。我想要的最终结果是实现一个 ActionListener，它会在用户单击按钮时删除标签。例如：当用户单击 JButton 时，从框架中删除 5 个标签之一。当他们再次单击该按钮时，剩余的 4 个标签中的一个将被删除……依此类推，直到剩下 0 个标签。从技术上讲，我让程序按要求工作，但是，我试图查看是否有一种方法可以通过循环来实现 ActionListener 事件，而不是为每个单独的标签列出一个 if 语句。非常感谢！

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

//calls for public class to inherit features of JFrame within Java
public class NoPurchaseReason extends JFrame implements ActionListener {

private int removeText = 0;

JButton btn = new JButton("Select");

JLabel lbl = new JLabel("Found better price");
JLabel lbl1 = new JLabel("Not as shown on website");
JLabel lbl2 = new JLabel("Wrong product");
JLabel lbl3 = new JLabel("Damaged upon delivery");
JLabel lbl4 = new JLabel("None of the above");

public static void main(String[] args) {
    JFrame f = new NoPurchaseReason("Please tell us why you wish to return your purchase.");
    f.setBounds(300, 100, 500, 500);
    f.setVisible(true);
    f.setBackground(Color.blue);
}

public NoPurchaseReason(String title) {
    super(title);
    setLayout(null);
    lbl.setBounds(40, 40, 600, 40);
    btn.setBounds(320, 10, 80, 20);
    lbl.setBounds(100, 40, 100, 20);
    lbl1.setBounds(100, 70, 100, 20);
    lbl2.setBounds(100, 100, 150, 20);
    lbl3.setBounds(100, 130, 100, 20);
    lbl4.setBounds(100, 160, 100, 20);

    add(btn);
    add(lbl);
    add(lbl);
    add(lbl1);
    add(lbl2);
    add(lbl3);
    add(lbl4);
    btn.addActionListener(this);
}

public void actionPerformed(ActionEvent e) {
    removeText++;
    if (removeText == 1) {
        lbl.setVisible(false);
        lbl1.setBounds(100, 40, 100, 20);
        lbl2.setBounds(100, 70, 100, 20);
        lbl3.setBounds(100, 100, 150, 20);
        lbl4.setBounds(100, 130, 100, 20);
    }
    if (removeText == 2) {
        lbl1.setVisible(false);
        lbl2.setBounds(100, 40, 100, 20);
        lbl3.setBounds(100, 70, 150, 20);
        lbl4.setBounds(100, 100, 100, 20);
    }
    if (removeText == 3) {
        lbl2.setVisible(false);
        lbl3.setBounds(100, 40, 150, 20);
        lbl4.setBounds(100, 70, 100, 20);
    }
    if (removeText == 4) {
        lbl3.setVisible(false);
        lbl4.setBounds(100, 40, 100, 20);
    }
    if (removeText == 5) {
        lbl4.setVisible(false);
    }
}

}

Answer 1

从长远来看，学习如何正确使用layout managers将为您省去很多麻烦。

您还会发现人们会告诉您遵守single responsibility principle，并避免创建违反此原则的类（例如，扩展 JFrame 和实现 ActionListener）。

您还会听到人们告诉您更喜欢使用操作而不是操作侦听器（也就是说，如果您需要在多个组件之间共享功能）。

一种简单的方法是将整个面板专门用于保存您的标签，然后简单地删除面板中的第一个标签，直到没有更多标签为止。这是一个例子：

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

class LabelDemo
{
    public static void main(String[] args) {
        String[] labels = {
                "Found better price",
                "Not as shown on website",
                "Wrong product",
                "Damaged upon delivery",
                "None of the above"
        };
        final JFrame frame = new JFrame();
        final JPanel panel = new JPanel();
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
        for (String s: labels) {
            panel.add(new JLabel(s));
        }
        frame.add(panel);
        JButton button = new JButton("Select");
        button.addActionListener(new ActionListener() {
            @Override public void actionPerformed(ActionEvent e) {
                if (panel.getComponentCount() > 0)
                    panel.remove(0);
                frame.repaint();
            }
        });
        frame.add(button, BorderLayout.NORTH);
        frame.pack();
        frame.setVisible(true);
    }
}

此外，您可能只是有一个我不知道的特定目标，但老实说，在这种情况下，列表似乎会更好。这也是一个例子：

String[] labels = {
        "Found better price",
        "Not as shown on website",
        "Wrong product",
        "Damaged upon delivery",
        "None of the above"
};
JList<String> list = new JList<>(labels);
int option = JOptionPane.showConfirmDialog(null, list, 
        "Please tell us why you wish to return your purchase.", 
        JOptionPane.OK_CANCEL_OPTION);
if (option == JOptionPane.OK_OPTION) {
    String selectedValue = list.getSelectedValue();
    System.out.println(selectedValue); // Do something with it.
}