线程"main"java.awt.AWTError中的异常:BoxLayout无法共享

Question

我在这段代码上收到此错误:

    super("Trace Masker");
    setLayout(new BoxLayout(getContentPane(), BoxLayout.PAGE_AXIS));

    label1 = new JLabel("Source directory:");
    label2 = new JLabel("Target directory:");
    label3 = new JLabel("Defect number:");
    label4 = new JLabel("Slice tokens:");
    label4.setToolTipText("Seperate multiple tokens with comma");

    txtSourceDirectory = new JTextField(30);
    txtTargetDirectory = new JTextField(30);
    txtDefectNumber = new JTextField(30);
    txtSliceTokens = new JTextField(30);

    btnBrowseSourceDirectory = new JButton("...");
    btnBrowseTargetDirectory = new JButton("...");
    btnStart = new JButton("Start");
    btnCancel = new JButton("Cancel");

    pnlLabels = new JPanel(new BoxLayout(pnlLabels, BoxLayout.PAGE_AXIS));
    pnlText = new JPanel(new BoxLayout(pnlText, BoxLayout.PAGE_AXIS));
    pnlBrowseButtons = new JPanel(new BoxLayout(pnlBrowseButtons, BoxLayout.PAGE_AXIS));
    pnlTop = new JPanel(new BoxLayout(pnlTop, BoxLayout.LINE_AXIS));
    pnlActionButtons = new JPanel(new FlowLayout(FlowLayout.RIGHT));

    pnlLabels.add(label1);
    pnlLabels.add(label2);
    pnlLabels.add(label3);
    pnlLabels.add(label4);

    pnlText.add(txtSourceDirectory);
    pnlText.add(txtTargetDirectory);
    pnlText.add(txtDefectNumber);
    pnlText.add(txtSliceTokens);

    pnlBrowseButtons.add(btnBrowseSourceDirectory);
    pnlBrowseButtons.add(btnBrowseTargetDirectory);

    pnlTop.add(pnlLabels);
    pnlTop.add(pnlText);
    pnlTop.add(pnlBrowseButtons);

    pnlActionButtons.add(btnStart);
    pnlActionButtons.add(btnCancel);

    add(pnlTop);
    add(pnlActionButtons);

错误在这一行:

pnlLabels.add(label1);

只是为了检查这是否与pnlLabels有关,我评论了它的所有行.然后错误发生在:

pnlText.add(txtSourceDirectory);

我已经在这里检查了其他2个问题并修复了JFrame的setLayout声明: Question1 Question2

Answer 1

您的问题来自以下行(以及所有其他行看起来相同):

pnlLabels = new JPanel(new BoxLayout(pnlLabels, BoxLayout.PAGE_AXIS));

当new BoxLayout(...)被调用时,pnlLabels仍然是null因为它尚未分配.正确的方法分为两步:

pnlLabels = new JPanel();
pnlLabels.setLayout(new BoxLayout(pnlLabels, BoxLayout.PAGE_AXIS);

问题应该消失(假设您对所有其他类似的代码行执行此操作).