Description Ondrej Chylik 2002-05-24 13:34:33 EDT

Steps to reproduce the bug:

* Run the class provided at the end of this report (any application (workbench 
or standalone) that uses the draw2d ScrollPane figure would do)

* "Tickle" one of the ScrollBars a little - try clicking an holding the mouse 
button in the area between one of the arrows and the dragable bar, so that the 
view scrolls to its bound, then use the same technique to scroll to the other 
bound. Repeat.

* After a while (rarely longer that, say, 20 seconds of "tickling") the scroll 
bar "sticks" to one of the boundaries and keeps scrolling that way whatever you 
do...

Furthermore:

* Now when you resize the window so that the viewport is large enough to 
contain its whole contents and the scrollbar(s) disappear, an exception is 
raised (the contents of stderr follows):

    org.eclipse.swt.SWTException: Failed to execute runnable 
(java.lang.NullPointerException)
        at org.eclipse.swt.SWT.error(SWT.java:1887)
        at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:148)
        at org.eclipse.swt.widgets.Display.syncExec(Display.java:1640)
        at com.ibm.etools.draw2d.ButtonModel$1.run(ButtonModel.java:396)
        at com.ibm.etools.draw2d.util.Timer.preformRun(Timer.java:38)
        at com.ibm.etools.draw2d.util.Timer.run(Timer.java:54)
        at java.lang.Thread.run(Thread.java:484)
    org.eclipse.swt.SWTException: Failed to execute runnable 
(java.lang.NullPointerException)
        at org.eclipse.swt.SWT.error(SWT.java:1887)
        at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages
(Synchronizer.java:96)
        at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:1389)
        at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:1211)
        at Bug.main(Bug.java:47)
    *** Stack trace of contained exception ***
    java.lang.NullPointerException
        at com.ibm.etools.draw2d.ButtonModel$2.run(ButtonModel.java:399)
        at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:29)
        at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages
(Synchronizer.java:93)
        at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:1389)
        at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:1211)
        at Bug.main(Bug.java:47)

* If you make the window smaller again, the scrollbars will reappear and will 
work corretly (however, you may reproduce the bug over and over again)


I succeeded to reproduce the bug everytime I intended to (even several times I 
didn't mean to do so, of course).
The bug doesn't seem to occur on the SWT ScrolledComposite control.

I use the version of GEF currently downloadable from 
http://download.eclipse.org/tools/gef/gef.zip

_____


A minimal ScrollPane example:

    import org.eclipse.swt.widgets.Display;
    import org.eclipse.swt.widgets.Shell;
    
    import com.ibm.etools.draw2d.LightweightSystem;
    import com.ibm.etools.draw2d.RectangleFigure;
    import com.ibm.etools.draw2d.ScrollPane;
    
    public class Bug {
    
        public static void main(String[] args) {
            Shell shell = new Shell();
            
            LightweightSystem lws = new LightweightSystem(shell);
            
            RectangleFigure rectangle = new RectangleFigure();
            rectangle.setPreferredSize(400, 300);
            
            ScrollPane scrollPane = new ScrollPane();
            scrollPane.setView(rectangle);
            
            lws.setContents(scrollPane);
            
            shell.setText("ScrollPane problem");
            shell.pack();
            shell.open();
            
            Display display = Display.getDefault();
            while (!shell.isDisposed()) {
                try {
                    if (!display.readAndDispatch()) {
                        display.sleep();
                    }
                } catch (RuntimeException re) {
                    re.printStackTrace();
                }
            }
        }
    }