Question

In my app I am trying to store an array of MKPolylines into NSUserDefaults.

NSData *data = [NSKeyedArchiver archivedDataWithRootObject:overlays];
[[NSUserDefaults standardUserDefaults] setObject:data forKey:@"theKey"];

Gives:

[MKPolyline encodeWithCoder:]: unrecognized selector sent to instance 0x169c20`
Terminating app due to uncaught exception 
'NSInvalidArgumentException', reason: '-
[MKPolyline encodeWithCoder:]: unrecognized 
selector sent to instance 0x1c57e0'

Edit: I made some progress. MKPolylineView conforms to the NSCoding protocol, so I have converted my array of MKPolylines into an array of MKPolylineViews. The problem is that when I want to add them back to a map later, I can’t convert them back to MKPolylines. Any idea how to do that?

Crashes at this code:

NSData* data = [[NSUserDefaults standardUserDefaults] objectForKey:@"theKey"];
NSArray* overlays = [NSKeyedUnarchiver unarchiveObjectWithData:data];

for(MKPolylineView* a in overlays)
    [mapView addOverlay:a.overlay];

2011-10-17 21:15:56.416 Trail Tracker[4269:707] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
*** First throw call stack:
(0x34b2f8bf 0x36c3a1e5 0x34a8420f 0x35697595 0x6257 0x62db 0x365f77ff 0x36601d53 0x36601cc1 0x366a1339 0x366a014f 0x366fad97 0x649b 0x36671565 0x366e9ce7 0x31fcc943 0x34b03a63 0x34b036c9 0x34b0229f 0x34a854dd 0x34a853a5 0x351f9fed 0x365ec743 0x2c75 0x2c34)
terminate called throwing an exception(gdb) 

Answer 1

I am not pretty sure about this but the MKPolylines are made from the array of CLLocationCoordinate2D which contains float value for lat and long.

So if you can convert this array of CLLocationCoordinate2D into array of dictionary I think than you can save those lines in your user defaults.

You can do some thing like this

MKMapPoint *points = overlays.points;

NSMutableArray *temp = [NSMutableArray array];
for(int i = 0; i < points.length; i++)
{
    // Not sure for this part
    NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:points[i].x], @"x", [NSNumber numberWithFloat:points[i].y], @"y", nil];
    [temp addObject:dict];
}

Then you can use this array to store the overlay points in nsuserdefaults like this

NSData *data = [NSKeyedArchiver archivedDataWithRootObject:temp];
[[NSUserDefaults standardUserDefaults] setObject:data forKey:@"theKey"];