Question

I am querying Google for lat/long points for a map view. This can take a long time depending on how many addresses the user has put into the app, as the map views all of them. I also introduced a short delay between querying in the for loop to make sure that Google gives me good results (if you query too quickly it doesn’t give you valid lat/long points but 0,0).

Because this takes so long, once the user presses the button to go to this UIViewController it takes a long time and I’m afraid the user will think the app is broken. I would ideally like the ViewController to “show up” but have an map (without annotations initially) with an animated activity indicator over the map until it’s finished querying, and then load the annotations. That way the user can look at the other information on the view while waiting for the map to load.

Here is my code:

- (void) viewDidLoad {
    [mapScroll startAnimating]; // activity indicator outlet
    [self makeMap];
    // ... etc.
}

- (void)makeMap {
allRegions = [[NSMutableArray alloc] init];
[self getDistinctRegions]; //generates allRegions array

double maxLat = -90;
double maxLon = -180;
double minLat = 90;
double minLon = 180;

for (int i=0; i<[allRegions count]; i++) {
    NSString *tempString = [allRegions objectAtIndex:i];
    NSString *searchString = [tempString stringByReplacingOccurrencesOfString:@" " withString:@"%20"];
    NSString *queryURL = [[NSString alloc] initWithFormat:@"http://maps.google.com/maps/geo?output=csv&q=%@",searchString];
    NSString *queryResults = [[NSString alloc] initWithContentsOfURL: [NSURL URLWithString:queryURL] encoding: NSUTF8StringEncoding error:nil];
    NSArray *queryData = [queryResults componentsSeparatedByString:@","];

    if ([queryData count] == 4) {
        double latitude = [[queryData objectAtIndex:2] doubleValue];
        double longitude = [[queryData objectAtIndex:3] doubleValue];

        if (latitude > maxLat) maxLat = latitude;
        if (latitude < minLat) minLat = latitude;
        if (longitude > maxLon) maxLon = longitude;
        if (longitude < minLon) minLon = longitude;

        CLLocationCoordinate2D coordinate;
        coordinate.latitude = latitude;
        coordinate.longitude = longitude;

        MKPlacemark *marker;
        marker = [[MKPlacemark alloc] initWithCoordinate:coordinate addressDictionary:nil];
        [mapView addAnnotation:marker];

        NSLog(@"%d",i);

        [NSThread sleepForTimeInterval:0.12];
    }
}

MKCoordinateRegion overallRegion;

double latSpan = abs(maxLat - minLat);
double lonSpan = abs(maxLon - minLon);
double avgLatitude = (maxLat+minLat)/2;
double avgLongitude = (maxLon+minLon)/2;

overallRegion.center.latitude = avgLatitude;
overallRegion.center.longitude = avgLongitude;
overallRegion.span.latitudeDelta = latSpan;
overallRegion.span.longitudeDelta = lonSpan;

[mapView setRegion:overallRegion animated:YES];

[mapScroll stopAnimating];
mapScroll.hidden = TRUE;
}

Answer 1

Um, quick and dirty solution, but here is the general process:

1) when user press Go button, you alloc-init your next view controller

2) assuming you have a method to download your lat/long info and a method to render your pin, in your next view controller’s viewDidLoad method, you can do something like:

-(void)viewDidLoad
{
    ....
    [self performSelectorInBackground:@selector(downloadMapData) withObject:nil];
}

// your download map data method
-(void)downloadMapData
{
    // download data from Google API. I assume you know how to do this part.

    // when done, add map annotation points to map on the main thread
    // interface changes must be done on the main thread
    [self performSelectorOnMainThread:@selector(addPinToMap)];
}