[news.eclipse.platform.swt] Re: [SWT] curious focus behaviour

[grant_gayed@xxxxxxxxxx (Grant Gayed)]

Andre,

#setFocus will set the focus in a platform-appropriate way, so this can
reveal differences between win32 and motif for instance (though it should
never cause a StackOverflow, unless it's a result of you having a focus-in
listener who reassigns focus elsewhere but the platform puts it in the
same place, thereby re-notifying your focus-in listener again, etc.).

#forceFocus should really force focus to the specified widget, so there
should not be a platform difference if you use this.  If you have a simple
test case that shows this behaving inconsistently then please log a bug
report with Platform - SWT.

Grant

Andre wrote:

> hello..

> I recently stumbled over some curious focus behaviour:
> if I call a widget's forceFocus() or setFocus() method, it works fine on
> SWT.WIN32 (XP) but doesn't on SWT.motif (Linux and Solaris) and SWT.photon
> (QNX). On SWT.gtk (Linux) it even may cause a stack overflow.

> My questions are: is that a bug or is that _really_ a platform specific
> behaviour? Is there I way to realy force a widget to get the focus - on
> every platform? I thought that if it's part of the API it should work
> everywhere..

> Thanks in advance
> Andre

> PS: a short sample code that demonstrates this problem:

> public class CuriousFocus
> {
> 	public static void main(String[] args)
> 	{
> 		Display display = new Display();
> 		Shell shell = new Shell(display);

> 		final Canvas widget1 = new Canvas(shell, SWT.BORDER);
>
		widget1.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_WHITE));		
> 		widget1.addFocusListener( new FocusListener()
> 		{
> 			public void focusGained(FocusEvent e)
> 			{
> 				System.out.println("widget1::focusGained()");
>
				widget1.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_RED));
> 				widget1.redraw();
> 			}

> 			public void focusLost(FocusEvent e)
> 			{
> 				System.out.println("widget1::focusLost()");
>
				widget1.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_WHITE));
> 				widget1.redraw();
> 			}
> 		});

> 		final Canvas widget2 = new Canvas(shell, SWT.BORDER);
>
		widget2.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_WHITE));
> 		widget2.addFocusListener( new FocusListener()
> 		{
> 			public void focusGained(FocusEvent e)
> 			{
> 				System.out.println("widget2::focusGained() \n");
>
				widget2.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_RED));
> 				widget2.redraw();
> 			}

> 			public void focusLost(FocusEvent e)
> 			{
> 				System.out.println("widget2::focusLost()");
>
				widget2.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_WHITE));
> 				widget2.redraw();

> 				// grab keyboard focus forever here
> 				widget2.forceFocus();
> 				//widget2.setFocus();
> 			}
> 		});


> 		shell.setLayout( new FillLayout());
> 		shell.open();

> 		//shell.setSize(200, 100);
> 		shell.pack();

> 		while (!shell.isDisposed())
> 		{
> 			if (!display.readAndDispatch())
> 			{
> 				display.sleep();
> 			}
> 		}
> 		display.dispose();
> 	}
> }