Bug 75988 [Preferences] IPreferencePage#performOk() returning false should prevent the dialog from closing
I think that if this method returns false, it should prevent the dialog from closing. Today, in order to perform validation I have to register key listeners to all fields an use #setValid(false) to disable the "OK" button.
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceDialog.java
* of the rightControl.
	 * @param composite
	 * @param rightControl
	 * @return Sash
	 */
	protected Sash createSash(final Composite composite, final Control rightControl) {
		final Sash sash = new Sash(composite, SWT.VERTICAL);
		sash.setLayoutData(new GridData(GridData.FILL_VERTICAL));
		
		
		sash.addListener(SWT.Selection, new Listener() {
			/*
			 * (non-Javadoc)
			 * 
			 * @see org.eclipse.swt.widgets.Listener#handleEvent(org.eclipse.swt.widgets.Event)
			 */
			public void handleEvent(Event event) {
				if (event.detail == SWT.DRAG)
					return;
				int shift = event.x - sash.getBounds().x;
				GridData data = (GridData) rightControl.getLayoutData();
				int newWidthHint = data.widthHint + shift;
				if (newWidthHint < 20)
					return;
				Point computedSize = getShell().computeSize(SWT.DEFAULT, SWT.DEFAULT);
				Point currentSize = getShell().getSize();
				
				
				boolean customSize = !computedSize.equals(currentSize);
				data.widthHint = newWidthHint;