JFrame - ActionListener

Question

我正在構建一個使用JFrame的程序。我最終想要的結果是實現一個ActionListener，當用戶單擊一個按鈕時它將刪除標籤。例如：當用戶點擊JButton時，5個標籤中的一個從框架中移除。當他們再次點擊該按鈕時，其餘的4個標籤中的一個被刪除...等等，直到剩下0個標籤。從技術上講，我有程序按要求工作，但是，我試圖看看是否有方法通過循環實現ActionListener事件，而不是爲每個單獨的標籤列出if語句。非常感謝！

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

學習如何正確使用layout managers會爲你節省很多的麻煩，從長遠來看。

你還會發現人們會告訴你要堅持single responsibility principle，並避免犯類違反這個原則的類（例如，擴展JFrame和實現ActionListener）。

你也會聽到人們告訴你比操作監聽器更喜歡使用動作（如果你需要跨多個組件共享功能，那就是）。

一個簡單的方法是專用整個面板來保存標籤，並直接刪除面板中的第一個標籤，直到沒有更多標籤。這裏有一個例子：

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); 
    } 
} 

而且，你可能只是心裏有一定的目標，我是不知道的，但說實話看起來像一個清單將是在這種情況下更好。這裏有一個例子：

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. 
}