Network reachability notification on status change is mandatory on iPhone?

Many reachability test codes seem to incorporate "notify" concept so that when network开发者_开发百科 gets back on, user can get notified.

1. Do I need to implement the "notification" part? Is it acceptable to alert user whenever he tries something that needs network connection and it is not available? (without notification when connection gets back)

2. I see example codes deals with pure network availability(if the device is connected to wifi, 3g, and so on) and with reachability to specific ip. My app needs to connect to specific ip address when appropriate. In this scenario, just alerting if that ip is not reachable in appropriate times are all that's required or do I need to handle something more?(such as putting different messages for alerting user to turn on network and for alerting user that my ip is not reachable)

Thank you

1. I'd recommend taking a look at Andrew Donoho's Reachability class that is an extension of the sample released by Apple:

http://blog.ddg.com/?p=24

That'll abstract away the need to worry about handling the notifications and allow you to focus on simply testing the reachability of your IP or if a certain network type is active.

2. In terms to actual notification to the user, I'd say that depends on your application. For instance on the vast majority of the screens on one of my Apps the UIView attempts to do an async download of data from a RESTful service when that view loads. I don't do any reachability tests beforehand, I simply attempt to make the call and if the request fails, I notify the user after the fact. Unless you have a specific case of needing to know an IP is reachable, I'd think in the general case handling any errors on connections attempts should be sufficient. I'm sure there are are plenty of edge cases though that you might want to test reachability first.

On the other hand I do use the reachability on a given screen that I recommend a WiFi connection. Since that screen performs a fairly data intensive sync, I warn the user if they are on 3G that the sync make take quite a bit longer vs. WiFi simply performs the sync.

1. AFAIK, there is no requirement that you pop up a notification when the network becomes available, or in fact that you actually pop up a notification when the network is not available. You could instead enable/disable network-related buttons (as long as the user can know why the buttons are disabled), display an unobtrusive on-screen indicator, or whatever.

   The important part is that you do not display a blank screen or a cryptic error message when the network is not available, or otherwise leave the user wondering why things aren't working.

2. I don't know of any requirement that you differentiate between "networking off" and "networking on but IP address unreachable".