XCode can't, but if you take your xcode project file and have OmniGraffle installed you can drag the project file over the OmniGraffle icon in your dock and it will map out all of your classes/delegates/protocols/etc. in a cool interactive graphic
Also, your code should be written in a way that doesn't have a predetermined 'flow'. The execution is based on user interaction and other events, so it wouldn't make sense to map it out into a flowchart