Java,SWT,FormLayout - 为什么我添加子项的顺序很重要？

Question

我正在使用FormLayout作为Composite容器.当我添加两个孩子标签和clientArea,其中clientArea要看标签上-在clientArea才会出现,当我第一次添加标签.

在添加子项后调用容器上的layout()没有帮助 - clientArea不会显示.

如何将子项添加到FormLayout控制的容器中,与彼此的依赖项无关？

MyLabel label;
Composite clientArea;   

public MyContainer(Composite parent, int style) {
    super(parent,style);

    //choose the container Layout
    FormLayout layout = new FormLayout();
    this.setLayout(layout);


    clientArea = new Composite(this, SWT.NONE);
    FormData formData4ClientArea = new FormData();
    formData4ClientArea.left = new FormAttachment(0,0);
    formData4ClientArea.top = new FormAttachment(0,5);
    formData4ClientArea.right = new FormAttachment(label,-5);
    formData4ClientArea.bottom = new FormAttachment(100,-5);
    //set the Formdata
    clientArea.setLayoutData(formData4ClientArea);
    clientArea.setBackground(getDisplay().getSystemColor(SWT.COLOR_GREEN));     


    //create the label
    label = new MyLabel(this, SWT.NONE);
    FormData formData4Label = new FormData();
    formData4Label.top = new FormAttachment(0,5);
    formData4Label.right = new FormAttachment(100,-5);
    formData4Label.bottom = new FormAttachment(100,-5);
    //set the FormData
    label.setLayoutData(formData4Label);

Answer 1

formData4ClientArea.right = new FormAttachment(label,-5);在这一点上,label是null.它没有实例化.所以基本上你将clientArea附加到任何东西.如果你想要clientArea附加label,ofc你需要首先实例化label,然后clientArea

但是,另一方面,为什么订单对你很重要？