Arndt Bieberstein Arndt Bieberstein - 3 months ago 19
Objective-C Question

property type or class using reflection

I was wondering if it's possible to determine the class or primitive type of an Objects properties. Getting all properties names and values is pretty easy. SO answer

So is there any way to get the properties class type while the property hast no value or nil value?

Example Code

@interface MyObject : NSObject
@property (nonatomic, copy) NSString *aString;
@property (nonatomic, copy) NSDate *aDate;
@property NSInteger aPrimitive;
@end

@implementation MyObject
@synthesize aString;
@synthesize aDate;
@synthesize aPrimitive;

- (void)getTheTypesOfMyProperties {
unsigned int count;
objc_property_t* props = class_copyPropertyList([self class], &count);
for (int i = 0; i < count; i++) {
objc_property_t property = props[i];

// Here I can easy get the name or value
const char * name = property_getName(property);

// But is there any magic function that can tell me the type?
// the property can be nil at this time
Class cls = magicFunction(property);
}
free(props);
}

@end

Answer

After searching through Apples Documentation about objc Runtime and according to this SO answer I finally got it working. I just want to share my results.

unsigned int count;
objc_property_t* props = class_copyPropertyList([MyObject class], &count);
for (int i = 0; i < count; i++) {
    objc_property_t property = props[i];
    const char * name = property_getName(property);
    NSString *propertyName = [NSString stringWithCString:name encoding:NSUTF8StringEncoding];
    const char * type = property_getAttributes(property);
    NSString *attr = [NSString stringWithCString:type encoding:NSUTF8StringEncoding];

    NSString * typeString = [NSString stringWithUTF8String:type];
    NSArray * attributes = [typeString componentsSeparatedByString:@","];
    NSString * typeAttribute = [attributes objectAtIndex:0];
    NSString * propertyType = [typeAttribute substringFromIndex:1];
    const char * rawPropertyType = [propertyType UTF8String];

    if (strcmp(rawPropertyType, @encode(float)) == 0) {
        //it's a float
    } else if (strcmp(rawPropertyType, @encode(int)) == 0) {
        //it's an int
    } else if (strcmp(rawPropertyType, @encode(id)) == 0) {
        //it's some sort of object
    } else {
        // According to Apples Documentation you can determine the corresponding encoding values
    }

    if ([typeAttribute hasPrefix:@"T@"]) {
        NSString * typeClassName = [typeAttribute substringWithRange:NSMakeRange(3, [typeAttribute length]-4)];  //turns @"NSDate" into NSDate
        Class typeClass = NSClassFromString(typeClassName);
        if (typeClass != nil) {
            // Here is the corresponding class even for nil values
        }
    }

}
free(props);