Jlabels在Gridlayout中是看不见的

Question

我做了一个jframe，其中添加了jpanel gridlayout。网格由jlabel组件，其中包含自定义号码。我没有例外。我的问题是在jframe（mainframe）上可见面板，但是您看不到添加到面板中的标签的数字。

有人能告诉我为什么我只看到面板，而不是标签？

首先，我创建GUI：

public Gui() {
    mainFrame = new JFrame();
    mainFrame.setResizable(false);
    mainFrame.setExtendedState(JFrame.MAXIMIZED_BOTH);
    mainFrame.setUndecorated(true);
    mainFrame.setLayout(null);
    mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

然后运行此方法：

public void startGame(Map map) {
    //Deletes every component that could be on the JFrame
    loescheAlles();

    //In the test are 100 paths in the String
    String[] paths = map.getPaths();
    //width has the value 1000
    int width = map.getBreite()*100;
    //height has the value 1000
    int height = map.getHoehe()*100;

    gamePanel = new JPanel();
    gamePanel.setBounds(0,0,width,height);
    gamePanel.setLayout(new GridLayout(width,height));

    JLabel[] label = new JLabel[paths.length];

    for(int i = 0; i<paths.length; i++) {
        //Text and border are not visible???
        label[i] = new JLabel("" + i);
        label[i].setBorder(new LineBorder(Color.BLACK));
        gamePanel.add(label[i]);
    }

    //Because I can see the Border on the JFrame I know, that the JPanel is visible.
    gamePanel.setBorder(new LineBorder(Color.BLACK));
    mainFrame.add(gamePanel);
}