Java 布局不显示组件(有时)

问题描述

我正在为我的学生编写一个 MathQuiz，包括用于渲染的 JLatexMath 和用于蜂鸣器的 jinput.问题是，有时(比如每四次)当我启动程序时，没有一个组件是可见的.它们在调整 JFrame 大小后出现.首先，我在考虑 jinput 或 jlatexMath 库中的错误，但即使使用这个最小的代码，我也会得到相同的错误:

I'm writing a MathQuiz for my pupils including JLatexMath for rendering and jinput for the buzzers. The problem is, that sometimes (like every fourth time) when I start the program, none of the components are visible. They appear after resizing the JFrame.First I was thinking of Bugs in the jinput or jlatexMath libraries, but I do get the same Error even with this minimal Code:

public class Shell extends JFrame{

  private JButton button1;
  private JButton button2;
  private Formula formula;

  public Shell() {
    super("blaBla");
    this.setSize(800, 600);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
    this.setLayout(new BoxLayout(this.getContentPane(), BoxLayout.Y_AXIS));
    Box b = Box.createHorizontalBox();
    button1 = new JButton(" ");
    button1.setEnabled(false);
    b.add(button1);
    b.add(Box.createHorizontalGlue());
    button2 = new JButton(" ");
    button2.setEnabled(false);
    b.add(button2);
    add(b);
    JPanel formulaPanel = new JPanel();
    add(Box.createVerticalStrut(20));
    add(formulaPanel);
  }

  public static void main(String[] args) {
    Shell s = new Shell();
  }
}

代码有什么问题?

推荐答案

首先将 setVisible(true); 移动到构造函数的末尾.

Start by moving setVisible(true); to the end of the constructor.

而不是在这里......

Instead of been here...

public Shell() {
    super("blaBla");
    this.setSize(800, 600);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
    //...
}

把它移到这里...

public Shell() {
    super("blaBla");
    //...
    add(Box.createVerticalStrut(20));
    add(formulaPanel);
    setVisible(true);
}

为了防止任何其他可能的图形故障，您应该始终从事件调度线程中启动您的 UI，请参阅 初始线程了解更多详情

To protect against any other possible graphical glitches, you should always start you UI's from within the Event Dispatching Thread, see Initial Threads for more details

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