Question

我正在尝试创建一个为用户提供按钮的GUI程序。单击此按钮时，它将显示textField并提示用户输入正则表达式。

以下是我迄今为止采取的步骤：

创建了一个JFrame并添加了一个按钮，标签和文本字段。
将文本字段可见性设置为＆＃34; false＆＃34;原来。标签和按钮可见性设置为＆＃34; true＆＃34;
实现ActionListener接口并覆盖ActionPerformed方法，将textField可见性更改为＆＃34; true＆＃34;单击按钮时。
将ActionListener实例注册到按钮。

当我以这种方式运行时，单击按钮后文本字段不可见（它编译得很好，但GUI中没有任何反应）

但是，如果我将标签可见性更改为＆＃34; false＆＃34;最初，然后添加一个动作设置为＆＃34; true＆＃34;在ActionListener中，它可以工作，并且标签和文本字段在单击按钮时变得可见。

我想知道的是，当ActionListener中包含标签时，文本字段才变为可见？

换句话说，为什么这段代码不起作用？

import java.awt.FlowLayout;
import java.awt.Container;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JTextArea;
import javax.swing.JScrollPane;
import javax.swing.JLabel;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class RegularExpressionGui extends JFrame {

  private final JLabel label1; //label
  private final JTextField textField1;
  private JTextField textField2; //text field
  private final JButton button1; //button
  private final JTextArea textArea1; //textArea

  public RegularExpressionGui() {

      super("Regular Expression Lookup");
      setLayout(new FlowLayout()); //GUI Layout

      //add the components

      label1 = new JLabel("Regular Expression");
      label1.setVisible(true);
      add(label1);

      textField1 = new JTextField("Enter Regular Expression here");
      textField1.setVisible(false);
      add(textField1);

      button1 = new JButton("Lookup Expression");
      add(button1);

      textArea1 = new JTextArea("Results");
      add(new JScrollPane(textArea1)); //makes the output area scrollable

      LookupHandler lookup = new LookupHandler();
      button1.addActionListener(lookup);
      textField1.addActionListener(lookup);

    } //end constructor 

  //inner class containing ActionListner 
  private class LookupHandler implements ActionListener {

    @Override
    public void actionPerformed(ActionEvent event) {

         if (event.getSource() == button1) {
          textField1.setVisible(true);

         }
       } 
  }

}

为什么这个工作呢？

import java.awt.FlowLayout;
import java.awt.Container;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JTextArea;
import javax.swing.JScrollPane;
import javax.swing.JLabel;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class RegularExpressionGui extends JFrame {

  private final JLabel label1; //label
  private final JTextField textField1;
  private JTextField textField2; //text field
  private final JButton button1; //button
  private final JTextArea textArea1; //textArea

  public RegularExpressionGui() {

      super("Regular Expression Lookup");
      setLayout(new FlowLayout()); //GUI Layout

      //add the components

      label1 = new JLabel("Regular Expression");
      label1.setVisible(false);
      add(label1);

      textField1 = new JTextField("Enter Regular Expression here");
      textField1.setVisible(false);
      add(textField1);

      button1 = new JButton("Lookup Expression");
      add(button1);

      textArea1 = new JTextArea("Results");
      add(new JScrollPane(textArea1)); //makes the output area scrollable

      LookupHandler lookup = new LookupHandler();
      button1.addActionListener(lookup);
      textField1.addActionListener(lookup);

    } //end constructor 

  //inner class containing ActionListner 
  private class LookupHandler implements ActionListener {

    @Override
    public void actionPerformed(ActionEvent event) {

               if (event.getSource() == button1) {
          textField1.setVisible(true);
          label1.setVisible(true);
         }
       } 
  }

}

Answer 1

我不是百分百肯定，但我认为你不需要内心阶层。

对于您的问题，如果删除了内部类，而是在ActionListener类上实现RegularExpressionGui，那么在pack()内添加actionPerformed它应该有效，因为pack()应该调用repaint方法。如果您调用第一个代码并调整窗口大小，您现在应该看到它，因为在调整大小时，布局管理器正在调用重绘方法。

所以，你的课程现在应该像这样：

import java.awt.FlowLayout;
import java.awt.Container;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JTextArea;
import javax.swing.JScrollPane;
import javax.swing.JLabel;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class RegularExpressionGui extends JFrame implements ActionListener {

  private final JLabel label1; //label
  private final JTextField textField1;
  private JTextField textField2; //text field
  private final JButton button1; //button
  private final JTextArea textArea1; //textArea

  public RegularExpressionGui() {

      super("Regular Expression Lookup");
      setLayout(new FlowLayout()); //GUI Layout

      //add the components

      label1 = new JLabel("Regular Expression");
      label1.setVisible(true);
      add(label1);

      textField1 = new JTextField("Enter Regular Expression here");
      textField1.setVisible(false);
      add(textField1);

      button1 = new JButton("Lookup Expression");
      add(button1);

      textArea1 = new JTextArea("Results");
      add(new JScrollPane(textArea1)); //makes the output area scrollable

      //LookupHandler lookup = new LookupHandler();
      button1.addActionListener(this);
      textField1.addActionListener(this);
      pack();
      setVisible(true);
      setDefaultCloseOperation(EXIT_ON_CLOSE);
    } //end constructor 

  //inner class containing ActionListner 
  @Override
  public void actionPerformed(ActionEvent event) {
       if (event.getSource() == button1) {
        textField1.setVisible(true);
        //label1.setVisible(true);
        pack();
       }
     } 
  public static void main (String args[]) {
    new RegularExpressionGui();
  }
}

如何在Java中单击按钮时使TextField可见？

1 个答案: