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
}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.dialogs.Dialog#buttonPressed(int)
	 */
	protected void buttonPressed(int buttonId) {
		switch (buttonId) {
		case IDialogConstants.OK_ID: {
			okPressed();
			return;
		}
		case IDialogConstants.CANCEL_ID: {
			cancelPressed();
			return;
		}
		case IDialogConstants.HELP_ID: {
			helpPressed();
			return;
		}
		}
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.dialogs.Dialog#cancelPressed()
	 */
	protected void cancelPressed() {
		
		Iterator nodes = preferenceManager.getElements(PreferenceManager.PRE_ORDER).iterator();