I've been working on a graphical user interface to enable a user to view, modify and add relevance judgments for a set of results returned by a search engine in response to a set of topics. The GUI was developed as part of some work I've been doing on the Text REtrieval Conference (TREC) 2012 Medical Records Track. I hope to write more about the GUI and the work on TREC in the future. For now, I want to share a solution I developed to a problem with the Java 6 Swing and AWT components I was struggling with over the past few days.
The problem was a JList contained within a JScrollPane contained within a JPanel that was resizing when new String elements added to the JList were longer than its current width. I initially implemented the GUI, which extends JFrame, using a BorderLayout:
The offending JList was in the West (leftmost) area, and when it grew (after adding a string longer than its initial width), it shrank the JTextArea component I have in the Center area. I wanted to prevent any resizing from happening.
I read that the Center area of a BorderLayout cannot be protected from resizing – it fills whatever space is available after all the other components have been rendered – so I experimented with different LayoutManagers (GridBagLayout and BoxLayout) … which will be the subject of a future blog post [update: see How to approximate BorderLayout with GridBagLayout or BoxLayout]. I couldn't manage to get GridBagLayout to work and play nicely with my components; BoxLayout – using a BoxLayout.X_AXIS JPanel for the West, Center and East area components, which was contained inside a BoxLayout.Y_AXIS JPanel (which was wedged between BoxLayout.Y_AXIS JPanels for North and South areas) – reduced the shrinking, but did not eliminate it.
I considered extending JPanel and overriding the getPreferredSize() or getMaximumSize() methods, but decided against this as the log files revealed that some resizing occurs after all the components in the GUI are initially populated. I wanted to allow the component sizes to settle into an initial populated state, and then prevent subsequent resizing.
After trying several other possibilities, I finally wrote a method to update the width associated with the PreferrredSize and MaximumSize, which I call after populating the components. I'll share it below, in case it is of use to others, or in case others have better solutions.
private void restrictPanelWidth(JPanel panel) {
int panelCurrentWidth = panel.getWidth();
int panelPreferredHeight = (int)panel.getPreferredSize().getHeight();
int panelMaximumHeight = (int)panel.getMaximumSize().getHeight();
panel.setPreferredSize(new Dimension(panelCurrentWidth, panelPreferredHeight));
panel.setMaximumSize(new Dimension(panelCurrentWidth, panelMaximumHeight));
}
Among the shortcomings of this solution is that any JPanel restricted by this method will not automatically resize if/when the containing window (JFrame) is resized. My expectation is that my GUI will fill the screen – however large that screen is – and that users will generally not want to make it any smaller than full screen. If my assumption proves unwarranted, I suppose I could reintroduce some flexibility via the componentResized() method of a ComponentAdapter, but I'm going to wait to see if any of the [currently] small group of users asks for this capability.
Update: I discovered another possible approach, which I have not now tried [see update 2 below], described in the Advanced JList Programming article at the Sun Developer Network (SDN). In the section entitled "JList Performance: Fixed Size Cells, Fast Renderers", Hans Muller suggests using the setFixedCellWidth() or setPrototypeCellValue() – which is passed a prototype (e.g., String) value that sets the cell width and cell height to the width and height of the prototype value – method to restrict the width of cells in a JList. He also notes "be sure to set the prototypeCellValue property after setting the cell renderer". The shortcoming I envision with this approach is that I would have to call setFixedCellWidth() any time that the window is resized … though, as noted before, this is a scenario I don't currently handle in the GUI anyway.
Update 2: When I loaded the GUI with a JList containing cells wider than the desired width, the original problem recurred, so my fix was not effective. I have since used setFixedCellWidth() for the two JLists in the West and East areas, and all is well in my [GUI] world again.