Size miscalculated when dynamically adding JPanels

Question

I am writing an application that is a virtual notebook. The idea is to have panels with various content (which is based on an external file) added to a panel that acts as a page. Once that page is full, its specialized add method should return false.

The problem is that I can't figure out how to accurately determine the size of the panels when I'm adding them, so I end up adding too many. The preferredSize of the panels is generally too short, and the size has 0 height. Is there a way to determine the exact size that a component is taking up in a layout?

I've tried using doLayout(), but it doesn't seem to change the size or preferredSize of my components. Maybe I'm not using it right? Here is the add method: (The contentPanel has BoxLayout, and the content panel doesn't have a set size, but is added to a panel (this) that does. The class this method is in extends JPanel)

public boolean addSpecializedgPanel(SpecializedPanel sp) {

    this.contentPanel.add(sp);

    this.doLayout();

    if (this.contentPanel.getSize().height > this.getHeight()) {
        this.contentPanel.remove(sp);
        return false;
    }

    return true;
}

Thanks for any help (even if it criticizes my whole design :) )! This has been a huge headache!

Answer 1

I don't think you should deal with the size like that, you should use a layout manager for that. Maybe you should have a look at How to use CardLayout

Answer 2

You want to use Container.validate() on the panel (possibly calling invalidate() first):

public void validate()

Validates this container and all of its subcomponents.

The validate method is used to cause a container to lay out its subcomponents again. It should be invoked when this container's subcomponents are modified (added to or removed from the container, or layout-related information changed) after the container has been displayed.

This should cause layout to occur, and, consequently, resizing of the components. You will then need to invalidate() after removing your failing panel, before returning false.