I'm trying to use ABRecordRef within an NSMutableArray, but it doesn't seem to work. I know that ABRecord is a C class, but I thought that ABRecordRef was the work around Objective-C class that allowed me to use it with NSObjects. What do I need to do to make this work?
What do you mean by "Not Working"? As in, you get compile or run-time errors?
As I noted in the response to the other poster, you can't use the Objective-C API on the iPhone (There also is no true ABrecord class to brdge to).
Generally it's a really good idea with the address book stuff on the iPhone to copy out elements you are interested in, and save the copied values off in something like a dictionary. If you need to save all the elements, you have to have code that reads every value as defined in the AddressBook.h header file, there's no API way to generically walk the records.
Also remember that at any time, the user might change the address book if they quit your app and come back - so be careful about what you change after they relaunch the app if you are storing values!!
Related
According to the Apple guideline , seems it is confusing, e.g. for method viewWithTag
In Java, I would have a method called
getViewByTag // Java version, equivalent to viewWithTag in Obj-C
But I also found there are some method like objectForKey, so why not just use objectWithKey instead?
getObjectByKey or just get // Java version, equivalent to objectForKey,
// but why not objectWithKey? Or not viewForKey above?
I actually think it is much simpler than what most answers think. I think it has less to do with complex programming language specifics, and has more to do with the uniqueness of the object in question.
When you say viewWithTag:, you are asking the UIView for any view that has that tag. There might be several. The UIView will return one of 'em.
However, objectForKey: (to me) sounds like there should be a single object (or nil) associated with that key. So, the key kinda exists and is bound (tightly coupled) to a single object.
EDIT:
There is an answer mentioning the existence of "by", which further implies how the convention has nothing to do with programming language complexities. It's just natural English.
NSString's stringByAppendingString:, for example, uses by, only because the function is written with a the verb appending. You can't say withAppending, that's bad English.
From my observation
While setting/getting the objects, you use WITH.
e.g. For setting of NSMutableArray object
- (id)initWithCapacity:(NSUInteger)numItems
While setting/getting the properties for objects, you use FOR.
e.g.For setting value for property of type NSMutableDictionary
- (void)setValue:(id)value forKey:(NSString *)key
Hope this helps in clearing your doubt
It seems like with is used for properties that directly belongs to an object. A UIView has a tag property so viewWithTag:14 could be rephrased as "Find the view whose tag property is 14".
When you put an object in a dictionary, associated to a key, this key is not necessarily part of the object itself. objectForKey:#"foo" is a way to say "Look for an object that's linked to the key "foo".
The Apple guidelines do not make any such claims as to when to use for or with. The point of the coding convention is to indicate what the types of the arguments may be and to write method signatures which are natural sounding.
The reason for the for or with in the method name is to identify the type or purpose of the first parameter to the method, which helps it read better.
Apple itself uses several conventions but that is the basic purpose, there is no concrete right or wrong just try to identify the first parameter of the method in the method name with either for or with.
And as for Apple conventions - get(whatever) is not even part of the actual conventions, so you could ask when do I use get or not.
Read this http://cocoadevcentral.com/articles/000082.php
also dont forget (by) NSURL urlByAppendingPathComponent etc - get a feel for it and you wont go wrong
You use "with" whenever the parameter is owned or to be owned, or will be a relatively permanent attribute by the object to the left of the "with" word.
initWithCapacity / arrayWithCapacity - the capacity will be an attribute of the container object being called and will be relatively permanent (until you add objects to it beyond the initial capacity)
viewWithTag – return a view "having" the specified "tag" attribute.
Whereas you use "for" to denote a looser association between the "desired" object and a "token" object that you use to get to it.
- objectForKey / attributeForValue – usually the "object" does not own the key.
- documentForWindow – the window is owned by the window controller and not the document. Furthermore there could be more than one window for each document.
But for looser associations of multiple
objects of the same type within a single method call, it's customary that you use something like:
doSomethingForFoo:withThisOtherFoo:havingYetAnotherFoo:
So the order for such complex call is:
for
with
having
How do I take a NSObject that I have set all the attributes of and then copy that into another block of memory that an array can use so I can re use the original one?
In short, you don't.
If you want to put the object in an array and then create a new object, do exactly that; addObject: to the array and alloc/init a new one.
If you are asking how you copy an object into, say, a random malloc() block somewhere -- say, in the middle of an array -- then that is a very different issue. It can technically be done, but basically no one does so as the frameworks and runtime aren't designed for that.
Without knowing more about your specific needs, it is impossible to go into more detail.
Making a copy of an object is done by sending it the copy message. This only works on instances of classes that implement the NSCopying protocol.
Read Implementing Copy for a good overview. Then read Implementing NSCopying Considered Harmful for some more background info.
I have an NSArray that contains two types of objects. Lets call them Apple and Orange.
Apple *myApple = [self.searchQueryResults objectAtIndex:indexPath.row];
When I am building my cell's I don't know what type is in my array, apples or oranges. How can I use the generic id type to store the object, and then cast appropriately?
You can use isKindOfClass:(Class)aClass to test the class type:
if ([myObject isKindOfClass:[Apple class]])
// do stuff
I'm not sure why you think you have to cast though. NSArray doesn't care what type of object you store in it, so when you pull it out, it'll still be the same object. But if you want you could still cast by doing something like
Apple *myApple = (Apple *)myObject;
Anyways, knowing the type of class it is should be enough for you to take appropriate action, since it's my understanding that you're showing both types in the same table, all you really need to do is appropriately display their different properties.
Don't mix types of classes in an NSArray.
You can do it, you can run checks for the type - but it's a really bad idea, UNLESS they are both part of the same subclass tree (say, both derivatives of Fruit). Then at least something looking in there can assume what kind of Fruit it might be, and check for particulars.
Basically you will save yourself a lot of headaches if you don't mix types in container classes, when somewhere down the road some bit of code figures for some reason there are only Apples in there but someone throws in a Pear. Then, BOOM!
The docs say:
The default implementation does not
copy attribute values. If the
attribute value may be mutable and
implements the NSCopying protocol (as
is the case with NSString, for
example), you can copy the value in a
custom accessor to help preserve
encapsulation (for example, in the
case where an instance of
NSMutableString is passed as a value).
So instead of getting into trouble and inconvenience with overwriting accessors in my NSManagedObject subclass, couldn't I simply do something like this?
myManagedObject.firstName = [[firstNameMutableStr copy] autorelease];
This would have the exact same effect, or not? The dynamic implementation would retain that anyways ... so.... why not the easy way?
It's an open question whether having to remember to copy the mutable string every where in code you set the attribute is "the easy way."
With a custom accessor, you just write the copy once then forget about. It copies automatically from that point on.
Just imagine that in thousands of lines of code you forgot to copy just once and developed a subtle bug because that one attribute of the managed object sporadically changed because some other totally unrelated code subsequently changed the mutable string you held only by reference.
I could tell you some stories of weekends lost to debugging because someone took "the easy way."
I know that there are functions in the objective-c runtime that allow you to create objects directly, such as class_createInstance. What I would like to know is if anything actually uses these functions other than the root classes' (NSObject) alloc method. I think things like KVC bindings might, but those aren't present on the iPhone OS (to my knowledge, correct me if I'm wrong), so is there anything that would do this?
In case you're wondering/it matters, I'm looking to allocate the size of an instance in a way that circumvents the objc runtime by declaring no ivars on a class, but overriding the +alloc method and calling class_createInstance(self, numberofbytesofmyivars).
Thanks
EDIT
I think I need to be more specific. I am adding classes to the runtime at runtime, and possibly unload and reload an altered version of the same class. I've worked around most of the issues so far, due to things like class_addMethod, but there's no equivalent for ivars after the class has been registered. The two solutions I can think of are having no actual ivars as far as the runtime is concerned, but overriding alloc to make sure I have enough room for them through extraBytes, or alternatively declaring an ivar which is a pointer to all of my actual ivars, which I can then obviously do whatever I want with. I would prefer to use the former strategy but there are a number of things that can go wrong, like if something allocates an instance of my object without going through my overloaded alloc method. Does anyone know of one of these things?
I'm not sure if you're trying to change the behavior of existing classes, which is not safe, or trying to do something for custom classes you own that are direct subclasses of NSObject, which probably is.
Almost all NSStrings you see in practice are instances of a private subclass, and that subclass allocates space for the string inline with the object. Like, instead of containing a pointer to a char*, the character data comes right after the ivars in the object. The extraBytes parameter in NSAllocateObject(Class aClass, NSUInteger extraBytes, NSZone *zone) is there for purposes such as this.
So on the one hand, yes, you can pull tricks like that. On the other, you need to know you're doing it with your stuff. If you try to do something like that with the private subclass of NSString (which is private, so you're only going to interact with through runtime introspection), you're probably going to conflict.
There are a few public cocoa classes that also do stuff like this, so you're best off if your classes inherit directly from NSObject. NSLock is one. The layout in memory for a custom subclass of NSLock looks like { isa, <ivars of NSLock> <ivars of subclass of NSLock> <more NSLock stuff, space reserved using the extraBytes parameter> }.
Also, just for the heck of it, note that +alloc calls +allocWithZone:, and +allocWithZone: is the more common override point.
I'm not sure why you'd want to do what you're suggesting--I don't see any reason you couldn't do it, but according to this post, there's usually no reason to use class_createInstance directly (I don't know of anything that uses it specifically). class_createInstance also doesn't take into account memory zones or other possible optimizations used by alloc. If you're just trying to hide your ivars, there are better ways.
EDIT: I think you're looking for the class_addIvar function, which (as the name suggests) dynamically adds an ivar to a class. It only works with the new runtime, so it won't work on the simulator, but it will work on the iPhone.
EDIT 2: Just to be totally clear (in case it wasn't already), you can definitely rely on allocWithZone always being called. Fundamental Cocoa classes, such as NSString and NSArray, override allocWithZone. class_createInstance is almost never used except at the runtime level, so you don't have to worry about any parts of Cocoa using it on your classes. So the answer to the original question is "no" (or more specifically, objects are sometimes created without alloc, but not without allocWithZone, at least as far as I know).
Well there is nothing technically to stop you from overriding alloc. Just create a method in your class called +alloc. I just can't imagine any reason why you would need to.
Sounds like you are trying too hard to manage memory. Let the OS dynamically allocate memory when you create an object. If you are using too much, the OS will send a notification that you are getting close to the limit. At that point you can dealloc stuff you don't need anymore.
If you need so much memory that you have to use tricks, your implementation may need rethinking at the core level instead of trying to fit your square design into the round hole of the iPhone OS.
Just my opinion based on the info you provided.