java - 使用单选按钮更改 JLabel 的字体时遇到问题

Question

我正在开发一个类(class)程序，但在获取一组单选按钮来更改 JLabel 的字体时遇到了困难。我有适用于粗体和斜体的 JCheckBoxes，但是字体单选按钮不起作用。我是否必须调用重新加载或重新绘制方法才能更新字体？我可以通过在 StyleListener 方法中使用类似的代码来更改字体，因此我感觉问题出在 FontListener 方法中。我也尝试过通过代码进行调试，似乎 FontListener 方法中的代码实际上没有执行任何操作。我错过了什么？

//********************************************************************
//  StyleOptionsPanel.java      adapted from Java Foundations
//
//  Demonstrates the use of check boxes.
//********************************************************************

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

public class StyleOptionsPanel extends JPanel
{
   private JLabel saying;
   private JCheckBox bold, italic;
   private JRadioButton courier, times, helv;
   private ButtonGroup fonts;
   private int style = Font.PLAIN;
   private String typeFace = "Helvetica";

   //-----------------------------------------------------------------
   //  Sets up a panel with a label and some check boxes that
   //  control the style of the label's font.
   //-----------------------------------------------------------------
   public StyleOptionsPanel()
   {
      saying = new JLabel ("Say it with style!");
      saying.setFont (new Font (typeFace, style, 20));

      bold = new JCheckBox ("Bold");
      bold.setBackground (Color.cyan);
      italic = new JCheckBox ("Italic");
      italic.setBackground (Color.cyan);

      JRadioButton courier = new JRadioButton("Courier");
      JRadioButton times = new JRadioButton("Times New Roman");
      JRadioButton helv = new JRadioButton("Helvetica");

      ButtonGroup fonts = new ButtonGroup();
      fonts.add(courier);
      fonts.add(times);
      fonts.add(helv);

      FontListener listener1 = new FontListener();
      courier.addActionListener(listener1);
      times.addActionListener(listener1);
      helv.addActionListener(listener1);

      StyleListener listener = new StyleListener();
      bold.addItemListener (listener);
      italic.addItemListener (listener);

      add(courier);
      add(times);
      add(helv);
      add (saying);
      add (bold);
      add (italic);

      setBackground (Color.cyan);
      setPreferredSize (new Dimension(300, 100));
   }

   //*****************************************************************
   //  Represents the listener for both check boxes.
   //*****************************************************************
   private class StyleListener implements ItemListener
   {
      //--------------------------------------------------------------
      //  Updates the style of the label font style.
      //--------------------------------------------------------------
      public void itemStateChanged (ItemEvent event)
      {
         style = Font.PLAIN;

         if (bold.isSelected())
            style = Font.BOLD;

         if (italic.isSelected())
            style += Font.ITALIC;

         saying.setFont (new Font (typeFace, style, 20));

      }
   }

   private class FontListener implements ActionListener{

     // Updates the font of the String variable saying
     public void actionPerformed(ActionEvent event){

      Object source = event.getSource(); 
      typeFace = "Helvetica";

      if(source == courier) typeFace = "Courier";

      else if(source == times) typeFace = "Times New Roman";

      else typeFace = "Helvetica";

      saying.setFont(new Font(typeFace, style, 20));

     }
   }
}

Answer 1

您没有在类中初始化单选按钮，它们为 null，因此 source 永远不会等于其中之一，并且始终为“Helvetica”。

您应该更改代码

JRadioButton courier = new JRadioButton("Courier");
JRadioButton times = new JRadioButton("Times New Roman");
JRadioButton helv = new JRadioButton("Helvetica");

至

courier = new JRadioButton("Courier");
times = new JRadioButton("Times New Roman");
helv = new JRadioButton("Helvetica");

为了初始化类字段并在 FontListener 中找到源代码。