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
* @param treeViewer
	 */
	protected void setTreeViewer(TreeViewer treeViewer) {
		this.treeViewer = treeViewer;
	}
	/**
	 * Get the composite that is showing the page.
	 * <strong>This API is experimental and may be deleted in
	 * the 3.1 timeframe</strong>.
	 * @return Composite.
	 */
	protected Composite getPageContainer() {
		return this.pageContainer;
	}
	/**
	 * Set the composite that is showing the page.
	 * <strong>This API is experimental and may be deleted in
	 * the 3.1 timeframe</strong>.
	 * @param pageContainer Composite
	 */
	protected void setPageContainer(Composite pageContainer) {
		this.pageContainer = pageContainer;
	}
	/**
	 * Create the page control for the supplied page.
	 */
	protected void createPageControl(IPreferencePage page, Composite parent) {
		page.createControl(parent);
	}
}