在动作中单击JButton时将JLabel设置为可见

问题描述

我试图让JLabel在单击JButton时出现。我添加了一个动作监听器，并将组件添加到了布局中。当在actionPerformed中单击JButton时，我正在使用label1.setVisible（true）。我仍然无法正常工作。可以看看我的代码吗？

I am trying to get a JLabel to appear when a JButton is clicked. I have added an action listener and added the component to the layout. I am using the label1.setVisible(true) when the JButton is clicked in actionPerformed. I still can't get it work. Can some look at my code?

public class LearnAppMain extends JFrame implements ActionListener {

// Define variables
public JButton button1;
public JLabel label1;
    public JTextField field1;

    private Image image1;
private String apple = "apple.jpg";

public LearnAppMain() {

    ImageIcon image1 = new ImageIcon(this.getClass().getResource(apple));
    JLabel label1 = new JLabel(image1);

    button1 = new JButton("A");
    button1.addActionListener(this);

    field1 = new JTextField(10);

    // Create layout
    setLayout(new FlowLayout());

    // create Container
    final Container cn = getContentPane();

    cn.add(button1);
    cn.add(field1);
    cn.add(label1);

    // setLayout(new FlowLayout());
    setSize(250, 250);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
}

@Override
public void actionPerformed(ActionEvent e) {

    Object source = e.getSource();

    if (e.getSource() == button1) {
        label1.setVisible(true);
        field1.setText("Apple");
    }

}

 }

I have my main method in another class file. The error I get leads me to the label1.setVisible(true);

每个问题我都看到他们说要这样做，但是我想知道是否有

Every question I've seen they say to do this, but I'm wondering if there is something else that needs to be added.

推荐答案

这里有几个问题：

• 您的 label1 通过在构造函数中执行 JLabel标签隐藏。您基本上在构造函数中声明了另一个名为 label1 的变量，该变量将其隐藏在类本身中。


• 您的标签在启动时可见-我使用了 label.setVisible（false）进行测试，但您可能希望以其他方式

• Your label1 was hidden by doing JLabel label in the constructor. You basically declared another variable called label1 in your constructor that hid the one in the class itself.
• Your label was visible on the startup - I used label.setVisible(false) for the test, but you might want otherwise

我还没有创建 Image ，因为我没有图像，所以请取消注释并适当更改。

I also put the creation of Image aside as I did not have an image, so uncomment that and change as appropriate.

这是一个完整的工作版本：

Here's a complete working version:

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

public class LearnAppMain extends JFrame implements ActionListener {

// Define variables
public JButton button1;
public JLabel label1;
    public JTextField field1;

    private Image image1;
private String apple = "apple.jpg";

public LearnAppMain() {

    //ImageIcon image1 = new ImageIcon(this.getClass().getResource(apple));
    //JLabel label1 = new JLabel(image1);
    label1 = new JLabel("hello");
    label1.setVisible(false);

    button1 = new JButton("A");
    button1.addActionListener(this);

    field1 = new JTextField(10);

    // Create layout
    setLayout(new FlowLayout());

    // create Container
    final Container cn = getContentPane();

    cn.add(button1);
    cn.add(field1);
    cn.add(label1);

    // setLayout(new FlowLayout());
    setSize(250, 250);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
}

@Override
public void actionPerformed(ActionEvent e) {

    Object source = e.getSource();

    if (e.getSource() == button1) {
        label1.setVisible(true);
        field1.setText("Apple");
    }

}
public static void main(String[] args) {
  new LearnAppMain();
}
}

我建议使用单独的（通常是内部类） ） ActionListener 实例，而不是覆盖 actionPerformed 实例。参见例如如果您对此感兴趣，可以使用类似的示例：

I'd suggest using separate (usually inner-class) ActionListener instances instead of overriding actionPerformed. See e.g. this for a similar example if you are interested:

• http://docs.oracle.com/javase/tutorial/displayCode.html?code=http://docs.oracle.com/javase/tutorial/uiswing/examples/events/BeeperProject/src/events/Beeper.java

此外，如果您在更大的应用程序中使用它（即不只是试验或用于原型设计），请确保所有Swing代码都在EDT上运行。

Also, if you are using this in a bigger application (i.e. not just experimenting or for prototyping), make sure all Swing code is run on EDT.

您通常使用。

希望这会有所帮助。

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