Is it possible to get an array of all of an object's properties in Objective C? Basically, what I want to do is something like this:
- (void)save {
NSArray *propertyArray = [self propertyNames];
for (NSString *propertyName in propertyArray) {
[self doSomethingCoolWithValue:[self valueForKey:propertyName]];
}
}
Is this possible? It seems like it should be, but I can't figure out what method my propertyNames up there should be.
I did some more digging, and found what I wanted in the Objective-C Runtime Programming Guide. Here's how I've implemented the what I wanted to do in my original question, drawing heavily from Apple's sample code:
#import <Foundation/NSObjCRuntime.h>
#import <objc/runtime.h>
- (void)save {
id currentClass = [self class];
NSString *propertyName;
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(currentClass, &outCount);
for (i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
propertyName = [NSString stringWithCString:property_getName(property)];
[self doSomethingCoolWithValue:[self valueForKey:propertyName]];
}
}
I hope this will help someone else looking for a way to access the names of an object's properties programatically.
dont forget
free(properties);
after the loop or you will get a leak. The apple documentation is clear:
An array of pointers of type objc_property_t describing the properties
declared by the class. Any properties declared by superclasses are not
included. The array contains *outCount pointers followed by a NULL
terminator. You must free the array with free().
Related
I have been interested in using something along the the lines of the following code to
automate the building of my objects (since there are many of them with quite a few properties):
MyObject *myObject = [[myObject alloc] init];
unsigned int numberOfProperties = 0;
objc_property_t *propertyArray = class_copyPropertyList([MyObject class], &numberOfProperties);
for (NSUInteger i = 0; i < numberOfProperties; i++)
{
objc_property_t property = propertyArray[i];
NSString *propertyName = [NSString stringWithUTF8String:property_getName(property)];
if (propertyName)
{
id valueForProperty = [myObject valueForKey:propertyName];
[myObject setValue:valueForProperty forKey:propertyName];
}
}
free(propertyArray);
However, what I've noticed is that this code will try to run not just on the properties in my header file, but also all of my implementation properties as well, which I do not want.
Since Objective-C doesn't actually distinguish public vs private properties, I am not sure how to do this. Any thoughts on how to indicate that I'm only interested in the properties in the header file to simulate the same thing effectively?
In short, you don't. This information is not available in the compiled program. You'd need to write a custom preprocessor to do this if you really wanted to.
I'm trying to dynamically determine the type of a property in Objective-C. Based on what I have read on this site and elsewhere, I believe I am doing the right thing. However, my code isn't working.
The code snippet below demonstrates the problem. Attempting to get the property information for "backgroundColor" and "frame", both of which are valid properties of UIView, fails (class_getProperty() returns NULL):
id type = [UIView class];
objc_property_t backgroundColorProperty = class_getProperty(type, "backgroundColor");
fprintf(stdout, "backgroundColorProperty = %d\n", (int)backgroundColorProperty); // prints 0
objc_property_t frameProperty = class_getProperty(type, "frame");
fprintf(stdout, "frameProperty = %d\n", (int)frameProperty); // prints 0
Enumerating the properties as described here doesn't produce the expected results, either. The following code:
NSLog(#"Properties for %#", type);
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(type, &outCount);
for (i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
fprintf(stdout, "%s %s\n", property_getName(property), property_getAttributes(property));
}
generates this output:
2012-03-09 13:18:39.108 IOSTest[2921:f803] Properties for UIView
caretRect T{CGRect={CGPoint=ff}{CGSize=ff}},R,N,G_caretRect
gesturesEnabled Tc,N
deliversTouchesForGesturesToSuperview Tc,N
skipsSubviewEnumeration Tc,N
viewTraversalMark Tc,N
viewDelegate T#"UIViewController",N,G_viewDelegate,S_setViewDelegate:
inAnimatedVCTransition Tc,N,GisInAnimatedVCTransition
monitorsSubtree Tc,N,G_monitorsSubtree,S_setMonitorsSubtree:
backgroundColorSystemColorName T#"NSString",&,N,G_backgroundColorSystemColorName,S_setBackgroundColorSystemColorName:
userInteractionEnabled Tc,N,GisUserInteractionEnabled
tag Ti,N,V_tag
layer T#"CALayer",R,N,V_layer
Documented properties such as "backgroundColor", "frame", and others are missing, whereas undocumented properties like "caretRect" and "gesturesEnabled" are included.
Any help would be very much appreciated. In case it is relevant, I'm seeing this behavior on the iOS simulator. I don't know if the same thing would happen on an actual device.
Thanks,
Greg
You are getting the UIView properties, the problem is backgroundColor is not a UIView property, is a category property. Check UIView.h. I think you can't get a objc_category, but have a look at class-dump.
Dodging around the issue slightly, the following works:
NSMethodSignature *signature = [[UIView class]
instanceMethodSignatureForSelector:#selector(backgroundColor)];
NSLog(#"%s", [signature methodReturnType]);
So the runtime may somehow have lost the fact that backgroundColor is a property but you seem to start with that information anyway in the first code snippet so it just checks out the return type of the getter.
You can find category properties as methods.
#import ObjectiveC;
static void test(Class class, NSString* methodName) {
Method method = class_getInstanceMethod(class, NSSelectorFromString(methodName));
const char* type = method_copyReturnType(method);
printf("%s : %s\n", methodName.UTF8String, type);
free((void*)type);
}
Then you inspect some...
test([UILabel class], #"alpha");
test([UILabel class], #"textColor");
test([UILabel class], #"isHidden");
test([UILabel class], #"minimumScaleFactor");
After look at these defines in runtime.h
#define _C_ID '#'
#define _C_CLASS '#'
#define _C_SEL ':'
#define _C_CHR 'c'
#define _C_UCHR 'C'
#define _C_SHT 's'
#define _C_USHT 'S'
#define _C_INT 'i'
#define _C_UINT 'I'
...
Don't forget to respect getters/setters notation for BOOL properties, search 'isHidden' instead 'hidden'.
I have two classes with the same set of properties, declared using the #property directive in a protocol, they both implement. Now I was wondering if it is possible to automatically populate an instance of the first class with the values from an instance of the second class (and vice-versa).
I would like this approach to be robust, so that if I change the of properties declared in the protocol there will be no need to add extra code in the copying methods.
Yes, given the exact context there could be various approaches to this problem.
One I can think of at the moment is to first get all the properties of source object then use setValue:value forKey:key to set the values on the target object.
Code to retrieve all custom properties:
-(NSSet *)propertyNames {
NSMutableSet *propNames = [NSMutableSet set];
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];
NSString *propertyName = [[[NSString alloc]
initWithCString:property_getName(property)] autorelease];
[propNames addObject:propertyName];
}
free(properties);
return propNames;
}
You may want to checkout the Key-Value Coding Programming Guide for more information.
I need a way to pass a property and get the name assigned to it. Any suggestions?
#property (nonatomic, retain) MyObject *crazyObject;
NSString *str = SOME_WAY_TO_GET_PROPERTY_NAME(crazyObject);
// Above method should return #"crazyObject"
You can try this:
unsigned int propertyCount = 0;
objc_property_t * properties = class_copyPropertyList([self class], &propertyCount);
NSMutableArray * propertyNames = [NSMutableArray array];
for (unsigned int i = 0; i < propertyCount; ++i) {
objc_property_t property = properties[i];
const char * name = property_getName(property);
[propertyNames addObject:[NSString stringWithUTF8String:name]];
}
free(properties);
NSLog(#"Names: %#", propertyNames);
It's as simple as this...expanding upon what Chuck already mentioned:
#ifndef STR_PROP
#define STR_PROP( prop ) NSStringFromSelector(#selector(prop))
#endif
You then use it like so:
NSString *strProp = STR_PROP(myProperty);
Background
Keep in mind that properties are really just, to quote Apple, "a syntactical shorthand for declaring a class’s accessor methods." In fact, by itself, the #property declaration doesn't even work. Your #synthesize statement translates the #property into the equivalent of two methods:
- (void)setCrazyObject:(MyObject *)something;
- (MyObject *)crazyObject;
Which one is used depends on the context surrounding your self.crazyObject. (#synthesize also creates a matching instance variable if you didn't do it yourself.) The offshoot of all this is that you can't really translate to and from a property with one single method.
Proposed Solution
You can use what Apple already provides:
NSString *foo = NSStringFromSelector(#selector(myClassProperty));
Or do something custom:
Given that self.crazyObject really translates to either [self crazyObject] or [self setCrazyObject:foo] by the time your code is running, ou'll probably need two methods, like:
- (NSString *)setterStringForProperty:(SEL)prop;
- (NSString *)getterStringForProperty:(SEL)prop;
You might then want at least 2 companion methods such as:
- (SEL)setterForPropertyName:(NSString *)propString;
- (SEL)getterForPropertyName:(NSString *)propString;
Within these methods, you can use the Foundation functions NSStringFromSelector and NSSelectorFromString to convert back and forth between SEL and NSString. Use whatever string manipulations you like to convert back and forth between your setter string (setCrazyObject) and your property name (crazyObject).
A complete solution is hard to provide without knowing the exact use case, but hopefully this provides some more clues for anyone trying to accomplish something similar. There might even be some useful things made possible by combining this approach with Oscar's answer.
Here is a function that returns the name of an ivar, so basically it not only returns the properties but any ivar of the class. I haven't found a way to get the property directly so I used the ivar trick.
#import <objc/objc.h>
/// -----
- (NSString *)nameOfIvar:(id)ivarPtr
{
NSString *name = nil;
uint32_t ivarCount;
Ivar *ivars = class_copyIvarList([self class], &ivarCount);
if(ivars)
{
for(uint32_t i=0; i<ivarCount; i++)
{
Ivar ivar = ivars[i];
id pointer = object_getIvar(self, ivar);
if(pointer == ivarPtr)
{
name = [NSString stringWithUTF8String:ivar_getName(ivar)];
break;
}
}
free(ivars);
}
return name;
}
After searching and debugging i find solution for me...
Added #import <objc/runtime.h>
Methods object_getIvar(id obj, Ivar ivar) send bad access and app crashes. i modify some code and it worked great:
+(NSString*)stringWithProperty:(id)property withClass:(id)controller
{
NSString *name = nil;
uint32_t ivarCount;
Ivar *ivars = class_copyIvarList([controller class], &ivarCount);
if(ivars)
{
for(uint32_t i=0; i<ivarCount; i++)
{
Ivar ivar = ivars[i];
name = [NSString stringWithUTF8String:ivar_getName(ivar)];
if ([controller valueForKey:name] == property)
{
break;
}
}
free(ivars);
}
return name;
}
Modifying the solution, it works when your object is allocated already, otherwise it returns nil:-
NSString * NSStringFromProperty(NSObject* property, NSObject* class)
{
unsigned int propertyCount = 0;
objc_property_t * properties = class_copyPropertyList([class class], &propertyCount);
NSString *name = nil;
for (unsigned int i = 0; i < propertyCount; ++i)
{
name = [NSString stringWithUTF8String:property_getName(properties[i])];
NSObject *object = [class valueForKey:name];
if (object != nil && object == property)
{
break;
}
else
{
name = nil;
}
}
free(properties);
return name;
}
You can use
NSString *str = NSStringFromSelector(#selector(crazyObject));
The good thing about this approach is that:
Xcode will autocomplete word crazyObject for you.
When later on you will change the property name from crazyObject to myCrazyObject, Xcode will add a warning saying "unrecognized selector!" -- pretty good for debugging.
I use this method so often, that I even created a function, which allows to write less letters:
NSString * __nonnull sfs(SEL __nonnull theSelector)
{
if (!theSelector)
{
abort();
}
return NSStringFromSelector(theSelector);
}
Now your final solution can look like this:
NSString *str = sfs(#selector(crazyObject));
From Get property name as string, without using the runtime reference library, just define:
#define propertyKeyPath(property) (#""#property)
#define propertyKeyPathLastComponent(property) [[(#""#property) componentsSeparatedByString:#"."] lastObject]
And then you can do something like this:
NSLog(#"%#", propertyKeyPathLastComponent(appleStore.storeLocation.street)); //result: street
You may check my approach at Gist to get the string for a property with autocompletion and compile-time check.
How to use:
Get the property name for a class:
#interface AnyClass : NSObject
#property (strong) NSData *data;
#end
// == My approach ==
// C string for a class
PropertyNameForClass(AnyClass, data); // ==> "data"
// NSString for a class
PropertyStringForClass(AnyClass, data); // ==> #"data"
// Bad approach (no autocompletion; no compile-time check):
NSString *propertyName = #"data";
Get the property name for a protocol:
#protocol AnyProtocol
#property (strong) NSDate *date;
#end
// C string for a protocol
PropertyNameForProtocol(AnyProtocol, date); // ==> "date"
// NSString for a protocol
PropertyStringForProtocol(AnyProtocol, date); // ==> #"date"
Unconventional, hacky, ugly, late, but... as strong-named as it gets and works like a charm:
#define SOME_WAY_TO_GET_PROPERTY_NAME(p) p == p ? [[[[[[[NSString alloc] initWithCString:#p encoding:NSUTF8StringEncoding] componentsSeparatedByString:#"."] lastObject] componentsSeparatedByString:#" "] lastObject] stringByReplacingOccurrencesOfString:#"]" withString:#""] : #""
Sample usage:
NSLog(SOME_WAY_TO_GET_PROPERTY_NAME(self.customer.surname)); // surname
NSLog(SOME_WAY_TO_GET_PROPERTY_NAME([[self customer] birthDate])); // birthDate
...
Say I have my class
#interface Person : NSObject { NSString *name; }
I need to get the name of NSString's within my class
Person *person = [[Person alloc] init];
NSLog(#"Name of variable %s\n", _NameofVariable_(person->name));
Thanks for the answers, here's the solution I came up from the replies
//returns nil if property is not found
-(NSString *)propertyName:(id)property {
unsigned int numIvars = 0;
NSString *key=nil;
Ivar * ivars = class_copyIvarList([self class], &numIvars);
for(int i = 0; i < numIvars; i++) {
Ivar thisIvar = ivars[i];
if ((object_getIvar(self, thisIvar) == property)) {
key = [NSString stringWithUTF8String:ivar_getName(thisIvar)];
break;
}
}
free(ivars);
return key;
}
As easy as
#define VariableName(arg) (#""#arg)
Then you do:
NSObject *obj;
NSString *str = VariableName(obj);
NSLog(#"STR %#", str);//obj
You can get the names of a class's instance variables with the Objective-C runtime API function class_copyIvarList. However, this is rather involved, rarely done and almost never the best way to accomplish something. If you have a more specific goal in mind than mere curiosity, it might be a good idea to ask about how to accomplish it in Objective-C.
Also, incidentally, person.name doesn't specify an instance variable in Objective-C — it's a property call. The instance variable would be person->name.
You might use preprocessor stringification and a bit of string twiddling:
NSUInteger lastIndexAfter(NSUInteger start, NSString *sub, NSString *str) {
NSRange found = [str rangeOfString:sub options:NSBackwardsSearch];
if(found.location != NSNotFound) {
NSUInteger newStart = NSMaxRange(found);
if(newStart > start)
return newStart;
}
return start;
}
NSString *lastMember(NSString *fullName) {
if(!fullName) return nil;
NSUInteger start = 0;
start = lastIndexAfter(start, #".", fullName);
start = lastIndexAfter(start, #"->", fullName);
return [fullName substringFromIndex: start];
}
#define NSStringify(v) (##v)
#define _NameofVariable_(v) lastMember(NSStringify(v))
If the person object is exposed as a property of the class, you can use objc_msgSend to get the value.
So, if you could access person using
[object person]
You could also do
objc_msgSend(object, "person")
For more details on message sending, including how to pass arguments to methods, see the Objective-C Runtime Programming Guide section on Messaging
The following works as a macro:
#define STRINGIZE(x) #x