NSMutableArray addobject with malloc'd struct

问题:

I'm having trouble with a snippet of code. I'm trying to add an instance of CLLocationCoordinate2D to a NSMutable array using the addObject method, but whenever the line is executed, my app crashes. Is there anything obvious wrong with this code?

The crash is on this line:

[points addObject:(id)new_coordinate];

Polygon.m:

#import "Polygon.h"

@implementation Polygon
@synthesize points;

- (id)init {
    self = [super init];
    if(self) {
        points = [[NSMutableArray alloc] init];
    }
    return self;
}


-(void)addPointLatitude:(double)latitude Longitude:(double)longitude {
    NSLog(@"Adding Coordinate: [%f, %f] %d", latitude, longitude, [points count]);
    CLLocationCoordinate2D* new_coordinate = malloc(sizeof(CLLocationCoordinate2D));
    new_coordinate->latitude = latitude;
    new_coordinate->longitude = longitude;
    [points addObject:(id)new_coordinate];
    NSLog(@"%d", [points count]);
}


-(bool)pointInPolygon:(CLLocationCoordinate2D*) p {
    return true;
}


-(CLLocationCoordinate2D*) getNEBounds {
    ...
}

-(CLLocationCoordinate2D*) getSWBounds {
    ...
}


-(void) dealloc {
    for(int count = 0; count < [points count]; count++) {
        free([points objectAtIndex:count]);
    }

    [points release];
    [super dealloc];
}

@end

回答1:

The proper way to do this is to encapsulate the data inside a NSValue, which is specifically for putting C types in NSArrays and other collections.

回答2:

You can only add NSObject-derived objects to an array. You should encapsulate the data inside a proper object (for example NSData).

For example:

CLLocationCoordinate2D* new_coordinate = malloc(sizeof(CLLocationCoordinate2D));
    new_coordinate->latitude = latitude;
    new_coordinate->longitude = longitude;
    [points addObject:[NSData dataWithBytes:(void *)new_coordinate length:sizeof(CLLocationCoordinate2D)]];
    free(new_coordinate);

retrieving the object:

CLLocationCoordinate2D* c = (CLLocationCoordinate2D*) [[points objectAtIndex:0] bytes];

回答3:

You can use the CFArrayCreateMutable function with custom callbacks to create a mutable array that doesn't retain/release.