Question

I have a model which can download data from a server and thus an activity indicator needs to be displayed (both in the status bar and on screen).

But I also have a UIWebView which is displaying content, the content has links, some are local and some are remote, if a remote link needs to be downloaded then an activity indicator needs to be displayed again.

What are design options for accomplishing this?

The app delegate could have methods to start and stop the activity indicators as directed by the models and controllers. But somehow this doesn’t seem quite clean to me – its starting to use the app delegate just as a bucket for dumping miscellaneous functionality.

I’m thinking the model should deal with its own activity indication and the controllers should deal with their own, i.e. separate them. However if I did that wouldn’t we then have the situation where a model is doing some UI related stuff (even if minimal)?

Is there a clean recommended solution?

Answer 1

IMO, Activity indicator is a View component independent of a specific view therefore it should be managed by your application delegate.

The way I tackled it is I created an ActivityManager class and I create and instance in my application delegate. It takes an instance of UIWindow and from that, I can determine how to center and display the indicator appropriately. All other areas of my application interact with this class through the observer pattern. They post notifications when the network state has changed and my activity manager evaluates the overall state of the application to see if it needs to either show or hide the indicator. Here is a sample of what you might see in my app:

ActivityManager *activityManager = [[ActivityManager alloc] initWithWindow:self.window];

self.activityManager = activityManager;

[activityManager release];

[self.activityManager addNotification:kNetworkStatusDidChangeNotification];

[self.activityManager addAsyncActivity:[HttpManager defaultManager]];

[self.activityManager startObserving];

I’ve added the ability to add new notifications so that way, when the manager observes these notification is can evaluate what needs to happen. AsyncActivity is just a protocol for singletons I can check to see if they are processing data. Then I just tell my manager to start observing. When I close my app I simply call:

[self.activityManager stopObserving];

to remove all observers and free up any memory. That should get you started in the right direction, I’m sure there are other ways to do it but that seems like the least invasive way to handle it to me. It’s also very portable.