在 Objective-C 中获取对象属性列表

The word "attributes" is a little fuzzy. Do you mean instance variables, properties, methods that look like accessors?

The answer to all three is "yes, but it's not very easy." The Objective-C runtime API includes functions to get the ivar list, method list or property list for a class (e.g., class_copyPropertyList()), and then a corresponding function for each type to get the name of an item in the list (e.g., property_getName()).

All in all, it can be kind of a lot of work to get it right, or at least a lot more than most people would want to do for what usually amounts to a really trivial feature.

Alternatively, you could just write a Ruby/Python script that just reads a header file and looks for whatever you'd consider "attributes" for the class.

I just managed to get the answer myself. By using the Obj-C Runtime Library, I had access to the properties the way I wanted:

- (void)myMethod {
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList([self class], &outCount);
for(i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
const char *propName = property_getName(property);
if(propName) {
const char *propType = getPropertyType(property);
NSString *propertyName = [NSString stringWithCString:propName
encoding:[NSString defaultCStringEncoding]];
NSString *propertyType = [NSString stringWithCString:propType
encoding:[NSString defaultCStringEncoding]];
...
}
}
free(properties);
}

This required me to make a 'getPropertyType' C function, which is mainly taken from an Apple code sample (can't remember right now the exact source):

static const char *getPropertyType(objc_property_t property) {
const char *attributes = property_getAttributes(property);
char buffer[1 + strlen(attributes)];
strcpy(buffer, attributes);
char *state = buffer, *attribute;
while ((attribute = strsep(&state, ",")) != NULL) {
if (attribute[0] == 'T') {
if (strlen(attribute) <= 4) {
break;
}
return (const char *)[[NSData dataWithBytes:(attribute + 3) length:strlen(attribute) - 4] bytes];
}
}
return "@";
}

When I tried with iOS 3.2, the getPropertyType function doesn't work well with the property description. I found an example from iOS documentation: "Objective-C Runtime Programming Guide: Declared Properties".

Here is a revised code for property listing in iOS 3.2:

#import <objc/runtime.h>
#import <Foundation/Foundation.h>
...
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList([UITouch class], &outCount);
for(i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
fprintf(stdout, "%s %s\n", property_getName(property), property_getAttributes(property));
}
free(properties);

@boliva's answer is good, but needs a little extra to handle primitives, like int, long, float, double, etc.

I built off of his to add this functionality.

// PropertyUtil.h
#import


@interface PropertyUtil : NSObject


+ (NSDictionary *)classPropsFor:(Class)klass;


@end




// PropertyUtil.m
#import "PropertyUtil.h"
#import "objc/runtime.h"


@implementation PropertyUtil


static const char * getPropertyType(objc_property_t property) {
const char *attributes = property_getAttributes(property);
printf("attributes=%s\n", attributes);
char buffer[1 + strlen(attributes)];
strcpy(buffer, attributes);
char *state = buffer, *attribute;
while ((attribute = strsep(&state, ",")) != NULL) {
if (attribute[0] == 'T' && attribute[1] != '@') {
// it's a C primitive type:
/*
if you want a list of what will be returned for these primitives, search online for
"objective-c" "Property Attribute Description Examples"
apple docs list plenty of examples of what you get for int "i", long "l", unsigned "I", struct, etc.
*/
return (const char *)[[NSData dataWithBytes:(attribute + 1) length:strlen(attribute) - 1] bytes];
}
else if (attribute[0] == 'T' && attribute[1] == '@' && strlen(attribute) == 2) {
// it's an ObjC id type:
return "id";
}
else if (attribute[0] == 'T' && attribute[1] == '@') {
// it's another ObjC object type:
return (const char *)[[NSData dataWithBytes:(attribute + 3) length:strlen(attribute) - 4] bytes];
}
}
return "";
}




+ (NSDictionary *)classPropsFor:(Class)klass
{
if (klass == NULL) {
return nil;
}


NSMutableDictionary *results = [[[NSMutableDictionary alloc] init] autorelease];


unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(klass, &outCount);
for (i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
const char *propName = property_getName(property);
if(propName) {
const char *propType = getPropertyType(property);
NSString *propertyName = [NSString stringWithUTF8String:propName];
NSString *propertyType = [NSString stringWithUTF8String:propType];
[results setObject:propertyType forKey:propertyName];
}
}
free(properties);


// returning a copy here to make sure the dictionary is immutable
return [NSDictionary dictionaryWithDictionary:results];
}








@end

I was able to get @orange80's answer to work WITH ARC ENABLED… ... for what I wanted - at least... but not without a bit of trial and error. Hopefully this additional information may spare someone the grief.

Save those classes he describes in his answer = as a class, and in your AppDelegate.h (or whatever), put #import PropertyUtil.h. Then in your...

- (void)applicationDidFinishLaunching:
(NSNotification *)aNotification {

method (or whatever) …

PropertyUtil *props  = [PropertyUtil new];
NSDictionary *propsD = [PropertyUtil classPropsFor:
(NSObject*)[gist class]];
NSLog(@"%@, %@", props, propsD);
…

The secret is to cast the instance variable of your class (in this Case my class is ABC0, and my instance of ABC0 is gist) that you want to query... to NSObject… (id), etc, won't cut it.. for various, weird, esoteric reasons. This will give you some output like so…

<PropertyUtil: 0x7ff0ea92fd90>, {
apiURL = NSURL;
createdAt = NSDate;
files = NSArray;
gistDescription = NSString;
gistId = NSString;
gitPullURL = NSURL;
gitPushURL = NSURL;
htmlURL = NSURL;
isFork = c;
isPublic = c;
numberOfComments = Q;
updatedAt = NSDate;
userLogin = NSString;
}

For all of Apple's unabashed / OCD bragging about ObjC's "amazeballs" "introspection... They sure don't make it very easy to perform this simple "look" "at one's self", "so to speak"..

If you really want to go hog wild though.. check out.. class-dump, which is a mind-bogglingly insane way to peek into class headers of ANY executable, etc… It provides a VERBOSE look into your classes… that I, personally, find truly helpful - in many, many circumstances. it is actually why I i started seeking a solution to the OP's question. here are some of the usage parameters.. enjoy!

    -a             show instance variable offsets
-A             show implementation addresses
--arch <arch>  choose a specific architecture from a universal binary (ppc, ppc64, i386, x86_64)
-C <regex>     only display classes matching regular expression
-f <str>       find string in method name
-I             sort classes, categories, and protocols by inheritance (overrides -s)
-r             recursively expand frameworks and fixed VM shared libraries
-s             sort classes and categories by name
-S             sort methods by name

I've found that boliva's solution works fine in the simulator, but on device the fixed length substring causes problems. I have written a more Objective-C-friendly solution to this problem that works on the device. In my version, I convert the C-String of the attributes to an NSString and perform string operations on it to get a substring of just the type description.

/*
* @returns A string describing the type of the property
*/


+ (NSString *)propertyTypeStringOfProperty:(objc_property_t) property {
const char *attr = property_getAttributes(property);
NSString *const attributes = [NSString stringWithCString:attr encoding:NSUTF8StringEncoding];


NSRange const typeRangeStart = [attributes rangeOfString:@"T@\""];  // start of type string
if (typeRangeStart.location != NSNotFound) {
NSString *const typeStringWithQuote = [attributes substringFromIndex:typeRangeStart.location + typeRangeStart.length];
NSRange const typeRangeEnd = [typeStringWithQuote rangeOfString:@"\""]; // end of type string
if (typeRangeEnd.location != NSNotFound) {
NSString *const typeString = [typeStringWithQuote substringToIndex:typeRangeEnd.location];
return typeString;
}
}
return nil;
}


/**
* @returns (NSString) Dictionary of property name --> type
*/


+ (NSDictionary *)propertyTypeDictionaryOfClass:(Class)klass {
NSMutableDictionary *propertyMap = [NSMutableDictionary dictionary];
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(klass, &outCount);
for(i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
const char *propName = property_getName(property);
if(propName) {


NSString *propertyName = [NSString stringWithCString:propName encoding:NSUTF8StringEncoding];
NSString *propertyType = [self propertyTypeStringOfProperty:property];
[propertyMap setValue:propertyType forKey:propertyName];
}
}
free(properties);
return propertyMap;
}

@orange80's answer has one problem: It actually doesn't always terminate the string with 0s. This can lead to unexpected results like crashing while trying to convert it to UTF8 (I actually had a pretty annoying crashbug just because of that. Was fun debugging it ^^). I fixed it by actually getting an NSString from the attribute and then calling cStringUsingEncoding:. This works like a charm now. (Also works with ARC, at least for me)

So this is my version of the code now:

// PropertyUtil.h
#import


@interface PropertyUtil : NSObject


+ (NSDictionary *)classPropsFor:(Class)klass;


@end




// PropertyUtil.m
#import "PropertyUtil.h"
#import <objc/runtime.h>


@implementation PropertyUtil


static const char *getPropertyType(objc_property_t property) {
const char *attributes = property_getAttributes(property);
//printf("attributes=%s\n", attributes);
char buffer[1 + strlen(attributes)];
strcpy(buffer, attributes);
char *state = buffer, *attribute;
while ((attribute = strsep(&state, ",")) != NULL) {
if (attribute[0] == 'T' && attribute[1] != '@') {
// it's a C primitive type:
/*
if you want a list of what will be returned for these primitives, search online for
"objective-c" "Property Attribute Description Examples"
apple docs list plenty of examples of what you get for int "i", long "l", unsigned "I", struct, etc.
*/
NSString *name = [[NSString alloc] initWithBytes:attribute + 1 length:strlen(attribute) - 1 encoding:NSASCIIStringEncoding];
return (const char *)[name cStringUsingEncoding:NSASCIIStringEncoding];
}
else if (attribute[0] == 'T' && attribute[1] == '@' && strlen(attribute) == 2) {
// it's an ObjC id type:
return "id";
}
else if (attribute[0] == 'T' && attribute[1] == '@') {
// it's another ObjC object type:
NSString *name = [[NSString alloc] initWithBytes:attribute + 3 length:strlen(attribute) - 4 encoding:NSASCIIStringEncoding];
return (const char *)[name cStringUsingEncoding:NSASCIIStringEncoding];
}
}
return "";
}




+ (NSDictionary *)classPropsFor:(Class)klass
{
if (klass == NULL) {
return nil;
}


NSMutableDictionary *results = [[NSMutableDictionary alloc] init];


unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(klass, &outCount);
for (i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
const char *propName = property_getName(property);
if(propName) {
const char *propType = getPropertyType(property);
NSString *propertyName = [NSString stringWithUTF8String:propName];
NSString *propertyType = [NSString stringWithUTF8String:propType];
[results setObject:propertyType forKey:propertyName];
}
}
free(properties);


// returning a copy here to make sure the dictionary is immutable
return [NSDictionary dictionaryWithDictionary:results];
}


@end

I was using function boliva provided, but apparently it stopped working with iOS 7. So now instead of static const char *getPropertyType(objc_property_t property) one can just use the following:

- (NSString*) classOfProperty:(NSString*)propName{


objc_property_t prop = class_getProperty([self class], [propName UTF8String]);
if (!prop) {
// doesn't exist for object
return nil;
}
const char * propAttr = property_getAttributes(prop);
NSString *propString = [NSString stringWithUTF8String:propAttr];
NSArray *attrArray = [propString componentsSeparatedByString:@","];
NSString *class=[attrArray objectAtIndex:0];
return [[class stringByReplacingOccurrencesOfString:@"\"" withString:@""] stringByReplacingOccurrencesOfString:@"T@" withString:@""];
}

If someone is in the need of getting as well the properties inherited from the parent classes (as I did) here is some modification on "orange80" code to make it recursive:

+ (NSDictionary *)classPropsForClassHierarchy:(Class)klass onDictionary:(NSMutableDictionary *)results
{
if (klass == NULL) {
return nil;
}


//stop if we reach the NSObject class as is the base class
if (klass == [NSObject class]) {
return [NSDictionary dictionaryWithDictionary:results];
}
else{


unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(klass, &outCount);
for (i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
const char *propName = property_getName(property);
if(propName) {
const char *propType = getPropertyType(property);
NSString *propertyName = [NSString stringWithUTF8String:propName];
NSString *propertyType = [NSString stringWithUTF8String:propType];
[results setObject:propertyType forKey:propertyName];
}
}
free(properties);


//go for the superclass
return [PropertyUtil classPropsForClassHierarchy:[klass superclass] onDictionary:results];


}
}

This implementation works with both Objective-C object types and C primitives. It is iOS 8 compatible. This class provides three class methods:

+ (NSDictionary *) propertiesOfObject:(id)object;

Returns a dictionary of all visible properties of an object, including those from all its superclasses.

+ (NSDictionary *) propertiesOfClass:(Class)class;

Returns a dictionary of all visible properties of a class, including those from all its superclasses.

+ (NSDictionary *) propertiesOfSubclass:(Class)class;

Returns a dictionary of all visible properties that are specific to a subclass. Properties for its superclasses are not included.

One useful example of the use of these methods is to copy an object to a subclass instance in Objective-C without having to specify the properties in a copy method. Parts of this answer are based on the other answers to this question but it provides a cleaner interface to the desired functionality.

Header:

//  SYNUtilities.h


#import <Foundation/Foundation.h>


@interface SYNUtilities : NSObject
+ (NSDictionary *) propertiesOfObject:(id)object;
+ (NSDictionary *) propertiesOfClass:(Class)class;
+ (NSDictionary *) propertiesOfSubclass:(Class)class;
@end

Implementation:

//  SYNUtilities.m


#import "SYNUtilities.h"
#import <objc/objc-runtime.h>


@implementation SYNUtilities
+ (NSDictionary *) propertiesOfObject:(id)object
{
Class class = [object class];
return [self propertiesOfClass:class];
}


+ (NSDictionary *) propertiesOfClass:(Class)class
{
NSMutableDictionary * properties = [NSMutableDictionary dictionary];
[self propertiesForHierarchyOfClass:class onDictionary:properties];
return [NSDictionary dictionaryWithDictionary:properties];
}


+ (NSDictionary *) propertiesOfSubclass:(Class)class
{
if (class == NULL) {
return nil;
}


NSMutableDictionary *properties = [NSMutableDictionary dictionary];
return [self propertiesForSubclass:class onDictionary:properties];
}


+ (NSMutableDictionary *)propertiesForHierarchyOfClass:(Class)class onDictionary:(NSMutableDictionary *)properties
{
if (class == NULL) {
return nil;
}


if (class == [NSObject class]) {
// On reaching the NSObject base class, return all properties collected.
return properties;
}


// Collect properties from the current class.
[self propertiesForSubclass:class onDictionary:properties];


// Collect properties from the superclass.
return [self propertiesForHierarchyOfClass:[class superclass] onDictionary:properties];
}


+ (NSMutableDictionary *) propertiesForSubclass:(Class)class onDictionary:(NSMutableDictionary *)properties
{
unsigned int outCount, i;
objc_property_t *objcProperties = class_copyPropertyList(class, &outCount);
for (i = 0; i < outCount; i++) {
objc_property_t property = objcProperties[i];
const char *propName = property_getName(property);
if(propName) {
const char *propType = getPropertyType(property);
NSString *propertyName = [NSString stringWithUTF8String:propName];
NSString *propertyType = [NSString stringWithUTF8String:propType];
[properties setObject:propertyType forKey:propertyName];
}
}
free(objcProperties);


return properties;
}


static const char *getPropertyType(objc_property_t property) {
const char *attributes = property_getAttributes(property);
char buffer[1 + strlen(attributes)];
strcpy(buffer, attributes);
char *state = buffer, *attribute;
while ((attribute = strsep(&state, ",")) != NULL) {
if (attribute[0] == 'T' && attribute[1] != '@') {
// A C primitive type:
/*
For example, int "i", long "l", unsigned "I", struct.
Apple docs list plenty of examples of values returned. For a list
of what will be returned for these primitives, search online for
"Objective-c" "Property Attribute Description Examples"
*/
NSString *name = [[NSString alloc] initWithBytes:attribute + 1 length:strlen(attribute) - 1 encoding:NSASCIIStringEncoding];
return (const char *)[name cStringUsingEncoding:NSASCIIStringEncoding];
}
else if (attribute[0] == 'T' && attribute[1] == '@' && strlen(attribute) == 2) {
// An Objective C id type:
return "id";
}
else if (attribute[0] == 'T' && attribute[1] == '@') {
// Another Objective C id type:
NSString *name = [[NSString alloc] initWithBytes:attribute + 3 length:strlen(attribute) - 4 encoding:NSASCIIStringEncoding];
return (const char *)[name cStringUsingEncoding:NSASCIIStringEncoding];
}
}
return "";
}


@end

These answers are helpful, but I require more from that. All I want to do is to check whether the class type of a property is equal to that of an existing object. All the codes above are not capable of doing so, because: To get class name of an object, object_getClassName() returns texts like these:

__NSArrayI (for an NSArray instance)
__NSArrayM (for an NSMutableArray instance)
__NSCFBoolean (an NSNumber object initialized by initWithBool:)
__NSCFNumber (an NSValue object initialized by [NSNumber initWithBool:])

But if invoking getPropertyType(...) from above sample code, wit 4 objc_property_t structs of properties of a class defined like this:

@property (nonatomic, strong) NSArray* a0;
@property (nonatomic, strong) NSArray* a1;
@property (nonatomic, copy) NSNumber* n0;
@property (nonatomic, copy) NSValue* n1;

it returns strings respectively as following:

NSArray
NSArray
NSNumber
NSValue

So it is not able to determine whether an NSObject is capable of being the value of one property of the class. How to do that then?

Here is my full sample code(function getPropertyType(...) is the same as above):

#import <objc/runtime.h>


@interface FOO : NSObject


@property (nonatomic, strong) NSArray* a0;
@property (nonatomic, strong) NSArray* a1;
@property (nonatomic, copy) NSNumber* n0;
@property (nonatomic, copy) NSValue* n1;


@end


@implementation FOO


@synthesize a0;
@synthesize a1;
@synthesize n0;
@synthesize n1;


@end


static const char *getPropertyType(objc_property_t property) {
const char *attributes = property_getAttributes(property);
//printf("attributes=%s\n", attributes);
char buffer[1 + strlen(attributes)];
strcpy(buffer, attributes);
char *state = buffer, *attribute;
while ((attribute = strsep(&state, ",")) != NULL) {
if (attribute[0] == 'T' && attribute[1] != '@') {
// it's a C primitive type:


// if you want a list of what will be returned for these primitives, search online for
// "objective-c" "Property Attribute Description Examples"
// apple docs list plenty of examples of what you get for int "i", long "l", unsigned "I", struct, etc.


NSString *name = [[NSString alloc] initWithBytes:attribute + 1 length:strlen(attribute) - 1 encoding:NSASCIIStringEncoding];
return (const char *)[name cStringUsingEncoding:NSASCIIStringEncoding];
}
else if (attribute[0] == 'T' && attribute[1] == '@' && strlen(attribute) == 2) {
// it's an ObjC id type:
return "id";
}
else if (attribute[0] == 'T' && attribute[1] == '@') {
// it's another ObjC object type:
NSString *name = [[NSString alloc] initWithBytes:attribute + 3 length:strlen(attribute) - 4 encoding:NSASCIIStringEncoding];
return (const char *)[name cStringUsingEncoding:NSASCIIStringEncoding];
}
}
return "";
}


int main(int argc, char * argv[]) {
NSArray* a0 = [[NSArray alloc] init];
NSMutableArray* a1 = [[NSMutableArray alloc] init];
NSNumber* n0 = [[NSNumber alloc] initWithBool:YES];
NSValue* n1 = [[NSNumber alloc] initWithBool:NO];
const char* type0 = object_getClassName(a0);
const char* type1 = object_getClassName(a1);
const char* type2 = object_getClassName(n0);
const char* type3 = object_getClassName(n1);


objc_property_t property0 = class_getProperty(FOO.class, "a0");
objc_property_t property1 = class_getProperty(FOO.class, "a1");
objc_property_t property2 = class_getProperty(FOO.class, "n0");
objc_property_t property3 = class_getProperty(FOO.class, "n1");
const char * memberthype0 = getPropertyType(property0);//property_getAttributes(property0);
const char * memberthype1 = getPropertyType(property1);//property_getAttributes(property1);
const char * memberthype2 = getPropertyType(property2);//property_getAttributes(property0);
const char * memberthype3 = getPropertyType(property3);//property_getAttributes(property1);
NSLog(@"%s", type0);
NSLog(@"%s", type1);
NSLog(@"%s", type2);
NSLog(@"%s", type3);
NSLog(@"%s", memberthype0);
NSLog(@"%s", memberthype1);
NSLog(@"%s", memberthype2);
NSLog(@"%s", memberthype3);


return 0;
}

You have three magic spells

Ivar* ivars = class_copyIvarList(clazz, &count); // to get all iVars
objc_property_t  *properties = class_copyPropertyList(clazz, &count); //to get all properties of a class
Method* methods = class_copyMethodList(clazz, &count); // to get all methods of a class.

Following piece of code can help you.

-(void) displayClassInfo
{
Class clazz = [self class];
u_int count;


Ivar* ivars = class_copyIvarList(clazz, &count);
NSMutableArray* ivarArray = [NSMutableArray arrayWithCapacity:count];
for (int i = 0; i < count ; i++)
{
const char* ivarName = ivar_getName(ivars[i]);
ivarArray addObject:[NSString  stringWithCString:ivarName encoding:NSUTF8StringEncoding]];
}
free(ivars);


objc_property_t* properties = class_copyPropertyList(clazz, &count);
NSMutableArray* propertyArray = [NSMutableArray arrayWithCapacity:count];
for (int i = 0; i < count ; i++)
{
const char* propertyName = property_getName(properties[i]);
[propertyArray addObject:[NSString  stringWithCString:propertyName encoding:NSUTF8StringEncoding]];
}
free(properties);


Method* methods = class_copyMethodList(clazz, &count);
NSMutableArray* methodArray = [NSMutableArray arrayWithCapacity:count];
for (int i = 0; i < count ; i++)
{
SEL selector = method_getName(methods[i]);
const char* methodName = sel_getName(selector);
[methodArray addObject:[NSString  stringWithCString:methodName encoding:NSUTF8StringEncoding]];
}
free(methods);


NSDictionary* classInfo = [NSDictionary dictionaryWithObjectsAndKeys:
ivarArray, @"ivars",
propertyArray, @"properties",
methodArray, @"methods",
nil];


NSLog(@"%@", classInfo);
}

For Swift onlookers, you can get this functionality by utilising the Encodable functionality. I will explain how:

1. Conform your object to Encodable protocol

   class ExampleObj: NSObject, Encodable {
   var prop1: String = ""
   var prop2: String = ""
   }
   

2. Create extension for Encodable to provide toDictionary functionality

    public func toDictionary() -> [String: AnyObject]? {
   let encoder = JSONEncoder()
   encoder.outputFormatting = .prettyPrinted
   guard let data =  try? encoder.encode(self),
   let json = try? JSONSerialization.jsonObject(with: data, options: .init(rawValue: 0)), let jsonDict = json as? [String: AnyObject] else {
   return nil
   }
   return jsonDict
   }
   

3. Call toDictionary on your object instance and access keys property.

   let exampleObj = ExampleObj()
   exampleObj.toDictionary()?.keys
   

4. Voila! Access your properties like so:

   for k in exampleObj!.keys {
   print(k)
   }
   // Prints "prop1"
   // Prints "prop2"