JViewport not drawing partially visible components

Question

I have a JViewport (no scrollbars; I control the viewPosition programatically).
Its View component is a JPanel containing left-to-right components in FlowLayout.
Sometimes if a component of the FlowLayout would be only partially visible, it does not get drawn at all.
If user resizes the window (and the viewport gets resized that way), the partially visible component is always drawn. (I am not even manually handling this Event.)
But if I programatically resize one of the FlowLayout components, then I expect the ones to the right to move accordingly. They do, but then if the last visible one becomes only partially visible as a result of the move, then it is not drawn AT ALL. Calling validate() on the FlowLayout-JPanel and on the JViewport does not seems to solve this.
Anyone know about this? Is it something that FlowLayout is doing on purpose?
/Mel

Answer 1

The reason that FlowLayout wraps my stuff when an already-contained component is widened but does not wrap when a new component is added (alway at the right; never on new row), is because the width field of the container component is not automatically changed upon the resize but must be recalculated upon the add.
I looked at code from FlowLayout's layoutContainer method (included below), and it appears that the decision to wrap is based solely upon the target container's existing width:
      int maxwidth = target.width - (insets.left + insets.right + hgap*2);
          // (where target is the container being laid out)
      if ((x == 0) || ((x + d.width) <= maxwidth)) // (where
                                                                             // x is the x-"pixel counter" for placing next component
                                                                             // d.width is width of the component being placed)
          then will be put on same row
      else
          will start a now rowHowever, while reading FlowLayout, I also discovered that its preferredLayoutSize method calculates a size for as if components were all on one row, i.e. returns width = (sum of all components + insets + hgaps), height = (max of all components + insets + vgaps). Therefore, I believe the simplest solution to my problem is to change the container's width field anytime a component resizing occurs, with the following line inserted right after the resize but before the validate:
[existing code that sets the label's new text, which used to be followed by validate()]
this.setSize(this.getLayout().preferredLayoutSize(this).width, this.getHeight());
validate();It works! (But I know it is making the calculation loop through all of the container's components occur more often than I would like in gui's event thread -- response doesn't look too bad though...)
/Mel