Unfortunately, Mantle 1.x doesn't have an easy way to apply an existing transformer (in this case, the transformer named MTLURLValueTransformerName) to each element of an array.
You can do it like this:
+ (NSValueTransformer*)imagesJSONTransformer {
NSValueTransformer *transformer = [NSValueTransformer valueTransformerForName:MTLURLValueTransformerName];
return [MTLValueTransformer transformerWithBlock: ^NSArray *(NSArray *values) {
NSMutableArray *transformedValues = [NSMutableArray arrayWithCapacity:values.count];
for (NSString *value in values) {
id transformedValue = [transformer transformedValue:value];
if (transformedValue) {
[transformedValues addObject:transformedValue];
}
}
return transformedValues;
}];
}
In Mantle 2.0, you'll be able to use the predefined array mapping transformer. Mantle 2.0 is still in development.