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
FormData messageData = new FormData();
		messageData.top = new FormAttachment(0);
		messageData.bottom = new FormAttachment(titleImage, 0, SWT.BOTTOM);
		messageData.right = new FormAttachment(titleImage, 0);
		messageData.left = new FormAttachment(0);
		return messageData;
	}
	/**
	 * @param parent
	 *            the SWT parent for the tree area controls.
	 * @return the new <code>Control</code>.
	 * @since 3.0
	 */
	protected Control createTreeAreaContents(Composite parent) {
		
		treeViewer = createTreeViewer(parent);
		treeViewer.setInput(getPreferenceManager());
		updateTreeFont(JFaceResources.getDialogFont());
		layoutTreeAreaControl(treeViewer.getControl());
		return treeViewer.getControl();
	}
	/**
	 * Create a new <code>TreeViewer</code>.
	 * 
	 * @param parent
	 *            the parent <code>Composite</code>.
	 * @return the <code>TreeViewer</code>.
	 * @since 3.0
	 */
	protected TreeViewer createTreeViewer(Composite parent) {