Redrawing markers on a Route-me map - ios

Question

Working in iOS 6, I cannot seem to get the map view to update itself to show markers added or removed.
When the app opens, a number of markers are placed on the map. The user can then make choices that add new markers and/or remove existing markers. This uses the same method as when the RMMarkerManager is populated at viewWillLoad, and I can iterate through the markers in the RMMarkerManager and see that it has the new set of markers, but the map view never updates to show them.
I have tried [mapview setNeedsDisplay] with no effect.
Clearly, I'm missing something that causes the mapview to update the display of the markers, but I have not figured out what, despite lots of head-scratching and digging through documentations and posts.
I will appreciate any suggestions as to what I should change or add.
As requested, here is the appropriate code. I'll explain how it works.
In the viewController's createMarkers method, the markers are created by accessing a sqlite database. One marker is created for each record that I want displayed as a marker on the map. I then iterate through the array of markers, adding each to the mapView's marketManager (addMarker method). The method createMarkers is called in the viewController's viewWillLoad method, and works correctly: all markers are displayed.
When using the app, a user can select or de-select records in the database. Then the viewController receives a notification that the user has changed the selection, and calls its setMarkers method. The mapview's marketmanager gets a removeMarkers message, then the marker array is re-created; it now has markers reflecting the user's selections. But the map never updates the on-view markers. Markers removed by the user are not removed on the view; markers added by the user are not added.
After the update, I can iterate through mapview.markermanager.markers and see that it now contains the new markers. But they're never shown on the mapView.
Class: Marker, subclass of RMMarker.
Simply holds data about the marker to be displayed
Marker.h:
// Marker.h
#import <Foundation/Foundation.h>
#import "Location.h"
#import "RMMarker.h"
#interface Marker : RMMarker {
NSString *category_name;
NSString *name;
NSString *desc;
NSString *address;
NSString *png;
int marker_id;
float lat;
float longi;
CLLocationCoordinate2D node;
float label_x_offset;
float label_y_offset;
}
#property (nonatomic, strong) NSString *category_name;
#property (nonatomic, retain) NSString *name;
#property (nonatomic, retain) NSString *desc;
#property (nonatomic, retain) NSString *address;
#property (nonatomic, retain) NSString *png;
#property (nonatomic) int marker_id;
#property (nonatomic) float lat;
#property (nonatomic) float longi;
#property (nonatomic) CLLocationCoordinate2D node;
#property (nonatomic) float label_x_offset;
#property (nonatomic) float label_y_offset;
#end
Class: Markers
Holds an NSMutableArray of Markers, which is populated from a sqlite database:
// Markers.m
#import "Markers.h"
#import "defs.h"
#import "FileLocator.h"
#import "Marker.h"
#implementation Markers
#synthesize markers;
-(NSMutableArray *) createMarkers {
markers = [[NSMutableArray alloc] init];
[self openDatabase];
NSString *query = [NSString stringWithFormat:#"SELECT categories.selected, categories.category_id, categories.png, places.name, address, description, latitude, longitude, place_id FROM places, categories WHERE (categories.selected = 1 AND places.category_id = categories.category_id);"];
debugPrintArgs(#"query: %#", query);
FMResultSet *rs = [db executeQuery:query];
while ([rs next]) {
Marker *marker = [[Marker alloc] init];
marker.marker_id = [rs intForColumn:#"place_id"];
marker.name = [rs stringForColumn:#"name"];
marker.address = [rs stringForColumn:#"address"];
marker.desc = [rs stringForColumn:#"description"];
marker.lat = [rs doubleForColumn:#"latitude"];
marker.longi = [rs doubleForColumn:#"longitude"];
marker.png = [rs stringForColumn:#"png"];
debugPrintArgs(#"%#, %#, %#, %f, %f", marker.name, marker.address, marker.description, marker.lat, marker.longi);
marker.label_y_offset = 150.0f;
marker.label_x_offset = 30.0f;
[markers addObject:marker];
}
[db close];
return markers;
}
#end
Methods in the viewcontroller:
setMarkers:
Iterates through the NSMUtableArray Markers, calling the method addMarker: for each marker in that array:
- (void) setMarkers {
// class Markers is essentially an NSMutableArray that holds instantiations of Marker - one for each marker to be displayed
// Markers is also responsible for populating itself from a sqlite database via the createMarkers method
Markers *markers = [[Markers alloc] init];
NSMutableArray *allMarkers = [markers createMarkers];
// allMarkers contains the markers to be displayed.
CLLocationCoordinate2D loc;
if ([allMarkers count] > 0) {
for (Marker *mrkr in allMarkers) {
loc.longitude = mrkr.longi;
loc.latitude = mrkr.lat ;
[self addMarker: mrkr at:loc withText:mrkr.name xOffset: mrkr.label_x_offset yOffset: mrkr.label_y_offset png: mrkr.png];
}
}
}
Also in the viewController: addMarker
And, finally, the addMarker method used to add a marker to the RMMarkerManager:
- (void) addMarker: (Marker *) marker at:(CLLocationCoordinate2D)loc withText:(NSString *)text xOffset: (float) x_offset yOffset:(float) y_offset png:(NSString *) png {
UIImage* markerImage = [UIImage imageNamed:png];
[marker replaceUIImage:markerImage anchorPoint:CGPointMake(0.38f, 1.08f)];
[viewMap.markerManager addMarker: marker AtLatLong: loc];
CGPoint position = CGPointMake( 0.0f, 0.0f);
[marker changeLabelUsingText: text position: position ];
}

Answer 1

The offending line here is in setMarkers:
Markers *markers = [[Markers alloc] init];
Making markers an instance variable and doing the alloc-init in the class's viewWillLoad method corrected the problem.
I wish I could explain this better, but I am unsure as to why this caused the problem. But, it's corrected now and I'll explore when I've got some time.