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
messageArea.showTitle(currentPage.getTitle(), currentPage.getImage());
	}
	/**
	 * Update the tree to use the specified <code>Font</code>.
	 * 
	 * @param dialogFont
	 *            the <code>Font</code> to use.
	 * @since 3.0
	 */
	protected void updateTreeFont(Font dialogFont) {
		getTreeViewer().getControl().setFont(dialogFont);
	}
	/**
	 * Returns the currentPage.
	 * @return IPreferencePage
	 */
	protected IPreferencePage getCurrentPage() {
		return currentPage;
	}
	/**
	 * Sets the current page.
	 * @param currentPage
	 */
	protected void setCurrentPage(IPreferencePage currentPage) {
		this.currentPage = currentPage;
	}
	/**
	 * Set the treeViewer.
	 * <strong>This API is experimental and may be deleted in
	 * the 3.1 timeframe</strong>.