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Currently I'm building an application which shows nearby advertisements based on the current location. When the user starts the application for the first time I want them to see a top 10 of nearby advertisements.

I'm having a slight problem with fetching the location on time. My problem is that the current location isn't fetched yet before the view is loaded. Of course there is the delegate UpdatedLocation, but this one gets fired multiple times. I guess it fires multiple times, because it wants to fetch the most accurate location?

So my question is; What can I do to 'wait' until the location is found and then start searching for advertisements?

Thanks in advance!

Regards, Mittchel

Mittchel
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  • Display some text that says that the location is being determined, along with a spinner. Once you've got a location, show the real view. Or do I miss something? – DarkDust Dec 19 '11 at 13:09
  • Yep, Like I stated it finds multiple locations so how can I determine which one (last) is the one I need? – Mittchel Dec 19 '11 at 13:11

4 Answers4

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You should update the view every time you get a (more accurate) location. So remember the last location and check whether horizontalAccuracy/verticalAccuracy have decreased (smaller = more accurate, but negative = invalid). Maybe even updating every time you get a new location would be better since the accuracy might not change but the position does (user is moving).

If you just show a list, you should remember the previous results. Fetch the new result and if they differ, update your list.

Abizern
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DarkDust
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  • Thats what gives me the problem, I can't update the view everytime. In my ViewDidLoad I'm fetching the results (and I want to have it this way). Meaning, if I update the view everytime it keeps trying to fetch results.. – Mittchel Dec 19 '11 at 13:23
  • @Mittchel: then don't load the view until you have sufficiently good location data. – progrmr Dec 19 '11 at 16:58
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When CLLocationManager gets an updated hit from the Core Location system, it fires its delegate's didUpdateToLocation:fromLocation: method. Inside that method, you want to do whatever you do when you get an updated location.

In your case, you'll want to check that new location's .horizontalAccuracy property to see that it's a high quality result. You also probably want to chuck the first few, because CL will give you the last hit of the last location session as your first hit of the new one.

Either way, that's the method where you want to do your fetching of data.

Dan Ray
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  • I will give that a try, thanks. But how am I sure to see when it's the LAST updated location? – Mittchel Dec 19 '11 at 13:28
  • @Mittchel: there is no LAST updated location, you can keep getting updates forever any time accuracy or location changes. When it is good enough, call `stopUpdatingLocation` and use what you have. – progrmr Dec 19 '11 at 17:06
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There is no one location, you get a series of locations from CL, one cached and then others varying in accuracy over time, getting better (or worse) accuracy, taking anywhere from 1 second to 10 minutes.

CL will start by giving you a cached location, which may be good enough for your purposes. If it's not too old (<60 seconds) and reasonable accuracy, go ahead and use the cached location, it will be the fasted result. Otherwise you have to wait for a sufficiently good accuracy (you have to decide what is sufficient, look at .horizontalAccuracy).

If you insist on having the location before viewDidLoad is called (viewWillAppear would be a better place) then you have to hold off pushing that viewController until you have a sufficient location. How you do that depends on how that view controller is being loaded.

progrmr
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Here is what I would do. Load your view, and in your viewDidAppear, call your method to update location. I have been using a nice open source project on github called MBProgressHUD. It will display a variety of progress indicators on the screen (that will also block the user from leaving your view) while it finishes its work. It also gives a visual feedback to the user that your app hasn't stalled and is working.

You will still need to sort out your accuracy issues, but the progress view gives you time to load the view and keep the user engaged while you pull in what you need. And keeps your UI fluid.

Bill Burgess
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