java - Swing java 中出现错误 - IllegalArgumentException

Question

尝试在框架上放置一些 Swing 组件。这段代码几天前还有效。现在不行了，什么也没有了。也许有人可以告诉我出了什么问题？

public static void main(String[] args) {
    JFrame mainFrame = new JFrame();
    mainFrame.setSize(500, 400); //Size of frame
    mainFrame.setTitle("Cinema City"); //Set title
    mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

    JLabel mainLabel = new JLabel("Welcome to Cinema City catalog!");
    JLabel actorLabel = new JLabel("Actors: ");
    JLabel laLabel = new JLabel("Last added: ");
    JLabel searchLabel = new JLabel("How to search ?");

    GridBagConstraints gbc = new GridBagConstraints();

    mainFrame.add(mainLabel, new GridBagConstraints(4, 0, 1, 3, 1, 1,
            GridBagConstraints.NORTH, GridBagConstraints.HORIZONTAL,
            new Insets(20, 160, 0, 0), 0, 0));

    mainFrame.add(actorLabel, new GridBagConstraints(0, 0, 1, 1, 1, 1,
            GridBagConstraints.NORTHWEST, GridBagConstraints.HORIZONTAL,
            new Insets(100, 0, 0, 0), 0, 0));

    mainFrame.setVisible(true);

这是错误:

Exception in thread "main" java.lang.IllegalArgumentException: cannot add to layout: constraint must be a string (or null)
at java.awt.BorderLayout.addLayoutComponent(Unknown Source)
at javax.swing.JRootPane$1.addLayoutComponent(Unknown Source)
at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at javax.swing.JFrame.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at GUI.main(GUI.java:40)

Answer 1

您实际上并未将布局设置为 GridBagLayout，因此它仍然是默认布局(即 FlowLayout)。

当然，只有 GridBagLayout 才能真正处理 GridBagConstraints。可以通过将声明更改为 JFrame mainFrame = new JFrame(new GridBagLayout());

来解决此问题