Encode All Properties of NSObject to NSData - ios

Question

So I'm new to iOS, but I'm a bit baffled by the complexity of a simple task. I'm trying to store my custom NSObject class called 'Vehicle' in NSUserDefaults. Obviously, this can't be done, so I'll need to encode it to NSDATA first. Fine.
But that means that I need to encode each property of the class as well in the decode...
Inside my Vehicle class...
- (void) encodeWithCoder: (NSCoder *) coder
{
[coder encodeInt: x forKey: #"x"];
[coder encodeInt: y forKey: #"y"];
[coder encodeInt: direction forKey: #"direction"];
} // encodeWithCoder
- (id) initWithCoder: (NSCoder *) coder
{
if (self = [super init]) {
x = [coder decodeIntForKey: #"x"];
y = [coder decodeIntForKey: #"y"];
direction = [coder decodeIntForKey: #"direction"];
}
return (self);
} // initWithCoder
If I end up adding a new property to the vehicle class, I've got to add the encode and decode logic too. This is the same for creating a copy of a class using CopyWithZone. This leaves 3 or 4 areas where adding a new property to a class can go wrong.
I currently program mostly in LabVIEW, and we have the ability to take a class, and feed it to an encoder, which will do all the versioning and property manipulation automatically.
So I guess my question is:
Is this not heard of in iOS?
If it's not possible, is there a way to enumerate through all properties in a class and write a function to do this automatically.

Answer 1

You can use the objective-c runtime to find all the properties of an object and decode them, but I wouldn't recommend it. If you'd ilke, I can create a simple example for you.
EDIT: Here's an example:
#import <objc/runtime.h>
void decodePropertiesOfObjectFromCoder(id obj, NSCoder *coder)
{
// copy the property list
unsigned propertyCount;
objc_property_t *properties = class_copyPropertyList([obj class], &propertyCount);
for (int i = 0; i < propertyCount; i++) {
objc_property_t property = properties[i];
char *readonly = property_copyAttributeValue(property, "R");
if (readonly)
{
free(readonly);
continue;
}
NSString *propName = [NSString stringWithUTF8String:property_getName(property)];
#try
{
[obj setValue:[coder decodeObjectForKey:propName] forKey:propName];
}
#catch (NSException *exception) {
if (![exception.name isEqualToString:#"NSUnknownKeyException"])
{
#throw exception;
}
NSLog(#"Couldn't decode value for key %#.", propName);
}
}
free(properties);
}
void encodePropertiesOfObjectToCoder(id obj, NSCoder *coder)
{
// copy the property list
unsigned propertyCount;
objc_property_t *properties = class_copyPropertyList([obj class], &propertyCount);
for (int i = 0; i < propertyCount; i++) {
objc_property_t property = properties[i];
char *readonly = property_copyAttributeValue(property, "R");
if (readonly)
{
free(readonly);
continue;
}
NSString *propName = [NSString stringWithUTF8String:property_getName(property)];
#try {
[coder encodeObject:[obj valueForKey:propName] forKey:propName];
}
#catch (NSException *exception) {
if (![exception.name isEqualToString:#"NSUnknownKeyException"])
{
#throw exception;
}
NSLog(#"Couldn't encode value for key %#.", propName);
}
}
free(properties);
}
__attribute__((constructor))
static void setDefaultNSCodingHandler()
{
class_addMethod([NSObject class], #selector(encodeWithCoder:), imp_implementationWithBlock((__bridge void *)[^(id self, NSCoder *coder) {
encodePropertiesOfObjectToCoder(self, coder);
} copy]), "v#:#");
class_addMethod([NSObject class], #selector(initWithCoder:), imp_implementationWithBlock((__bridge void *)[^(id self, NSCoder *coder) {
if ((self = [NSObject instanceMethodForSelector:#selector(init)](self, #selector(init))))
{
decodePropertiesOfObjectFromCoder(self, coder);
}
return self;
} copy]), "v#:#");
}
This allows you to encode any object that exposes enough properties to reconstruct itself.