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.
Related
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.
It's possible to get list of classes from a bundle via NSBundleDidLoadNotification. But I can't figure out how I can get them from already loaded bundle. (same bundle with code)
I'm trying to get class list of my application bundle. More specifically, the classes only in my application binary.
I looked at objc_getClassList, but it returns ALL classes and it's obviously too heavy for me. I need lightweight method. I found objc_copyClassNamesForImage by googling, but it's not documented, and I don't know how to use it safely. I think I can try to use it conventionally, but I want to find another more safe option before going there.
Another option would be to iterate through all the classes registered with the runtime and use +[NSBundle bundleForClass:] on each one to figure out which one it came from. You can then sort things into sets based on the result.
Something like this:
#interface NSBundle (DDAdditions)
- (NSArray *)definedClasses_dd;
#end
#implementation NSBundle (DDAdditions)
- (NSArray *)definedClasses_dd {
NSMutableArray *array = [NSMutableArray array];
int numberOfClasses = objc_getClassList(NULL, 0);
Class *classes = calloc(sizeof(Class), numberOfClasses);
numberOfClasses = objc_getClassList(classes, numberOfClasses);
for (int i = 0; i < numberOfClasses; ++i) {
Class c = classes[i];
if ([NSBundle bundleForClass:c] == self) {
[array addObject:c];
}
}
free(classes);
return array;
}
#end
Then you can call:
NSLog(#"%#", [[NSBundle mainBundle] definedClasses_dd]);
Try this magic:
- (NSArray *)getClassNames {
NSMutableArray *classNames = [NSMutableArray array];
unsigned int count = 0;
const char **classes = objc_copyClassNamesForImage([[[NSBundle mainBundle] executablePath] UTF8String], &count);
for(unsigned int i=0;i<count;i++){
NSString *className = [NSString stringWithUTF8String:classes[i]];
[classNames addObject:className];
}
return classNames;
}
I could find some example for the function objc_copyClassNamesForImage at here.
http://www.opensource.apple.com/source/objc4/objc4-493.9/test/weak.m
// class name list
const char *image = class_getImageName(objc_getClass("NotMissingRoot"));
testassert(image);
const char **names = objc_copyClassNamesForImage(image, NULL);
testassert(names);
testassert(classInNameList(names, "NotMissingRoot"));
testassert(classInNameList(names, "NotMissingSuper"));
if (weakMissing) {
testassert(! classInNameList(names, "MissingRoot"));
testassert(! classInNameList(names, "MissingSuper"));
} else {
testassert(classInNameList(names, "MissingRoot"));
testassert(classInNameList(names, "MissingSuper"));
}
free(names);
The source code is unofficial but from Apple. So I decided to use this code until I find any better way.
I'm not sure if I worded the subject correctly. I am looping through an array, within each loop I am trying to instantiate a class, but I want to dynamically create the name. Like so:
int i = 0;
for(NSString* thisdatarow in filedata) {
i++;
NSString* thisad = [NSString stringWithFormat:#"ad%d", i];
NSLog(#"%#", thisad);
AdData* thisad = [AdData new];
}
In the example above I want AdData* thisad... to be named dynamically - "ad1", "ad2", "ad3"...and so on. I get a conflicting type error.
This code also generated an error:
int i = 0;
for(NSString* thisdatarow in filedata) {
i++;
AdData* [NSString stringWithFormat:#"ad%d", i] = [AdData new];
}
Is there a way to do this?
You can't do that in Objective-C.
Use a NSString to AdData map--it'll do basically the same thing!
**edit: To clarify, use an:
NSMutableDictionary *dict;
with keys that are NSString* objects containing the ad names, and values that are the AdData* objects.
i.e.
[dict setValue:ad1 forKey:#"ad1"];
to set the values, and
[dict valueForKey:#"ad1"];
to get the values. (ignore the obvious memory leaks there with the strings...)
This isn't possible. While Objective-C is very dynamic, it's not that dynamic.
The suggested way to do this would be to create your instances and put them into an array, not assigning them to explicitly named variables.
You can then refer to them individually using their index in the array.
Something like this:
NSMutableArray *ads = [NSMutableArray array];
for(NSString* thisdatarow in filedata) {
AdData* thisad = [[[AdData alloc] init] autorelease];
[ads addObject:thisad];
}
// get third ad:
AdData *ad = [ads objectAtIndex:2];
Alternatively you could create an NSDictionary, if you really want to refer to them by a name, like this:
NSMutableDictionary *ads = [NSMutableDictionary dictionary];
int i = 0;
for(NSString* thisdatarow in filedata) {
i++;
AdData* thisad = [[[AdData alloc] init] autorelease];
NSString *keyName = [NSString stringWithFormat:#"ad%d", i];
[ads setObject:thisad forKey:keyName];
}
// get third ad
AdData *ad = [ads objectForKey:#"ad2"];
Cant be done Without using a C array, which would look like this:
AdData **ad = malloc(sizeof(AdData) * numberOfAds);
ad[1] = [AdData new];
// etc.
if (ad)
free(ad);
But I don't know how that would work because of how Objective-C classes are stored....
Local variable names are a purely compile-time concept. So you cannot do anything "dynamic" (i.e. at runtime) with it. The compiler is free to rename the variables and add or remove variables as it sees fit.
If you think about it, what is the point of dynamically manipulating local variable names? In order to use the dynamically-named variable again, you must either 1) explicitly refer to the variable name, in which case you have hard-coded the name (not so dynamic), or 2) dynamically construct the name again. If it's (1), then there is only a fixed set of variable names, so dynamic-ness is unnecessary. If it's (2), you're missing the point of local variable names (the whole point of which is so they can be referred to explicitly).
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().
The object in question consists of key/value pairs aka #property. Is there an elegant way to encode/decode this object to a dictionary? It seems brute force to manually pull out each attribute and create the dictionary by hand.
Does it absolutely need to be a dictionary? Because NSKeyedArchiver gives you the memento-stored-by-key behaviour without actually being an NSDictionary - and has the added bonus that it can archive many objects which property-list serialization doesn't automatically support. There's a good description of using archivers and unarchivers on the CocoaDev wiki.
Objective-C's "object as dictionary" support comes through Key-Value Coding:
NSArray *myAttributes; // Assume this exists
NSDictionary *dictRepresentation = [object dictionaryWithValuesForKeys:myAttributes];
If the keys you desire are ObjC-2.0 properties of the class in question, you could do something similar to the following:
// Assume MyClass exists
unsigned int count = 0;
objc_property_t *properties = class_copyPropertyList([myClassInstance class], &count);
NSMutableDictionary *propertiesDict = [NSMutableDictionary dictionary];
unsigned int i;
for(i = 0; i < count; ++i) {
NSString *propertyName = [NSString stringWithCString:property_getName(properties[i]) encoding:NSASCIIStringEncoding];
id propertyValue = [self valueForKey:propertyName];
if(propertyValue)
[propertiesDict setObject:propertyValue forKey:propertyName];
}
free(properties), properties = NULL;
// Do something with propertiesDict
This could also be a simple class extension.