I have found the class PSCellularDataSettingsDetail and its method +(void)setEnabled:(BOOL)enabled;, which I think will give me what I need, which is accessing the mobile data setting.
I found this method by opening up the compiled Preferences.framework using class-dump-z.
Now I found this answer and tried to access the class and method that way, but the class is private too. How can I open this class up to Xcode?
Have you tried calling performSelector? That is usually the trick to call private methods. Remember all that makes a method private in Objective-C is the fact that it is not advertised in the h file. But if you send a message to an object and the object can respond to that message it will, regardless of what's in the header file.
If it's a class method like +(void)setEnabled you would just call [MyClass performSelector(#selector(myMethod)] and if it is an instance method you would call it on a variable that is an instance of the class:
MyClass *c = [[MyClass alloc] init];
[c performSelector: #selector(myMethod)]
It gets tricky when you need to pass parameters though like in this case, because the only way performSelector can pass parameters is if they are objects not primitives. You can also look into using objc_msgSend.
There is a ton of stuff online explaining how those two work. Either way it's messy to try to call private methods and is very risky.
Related
I try to dynamically call certain viewController/Feature depends on his Name.NSClassFromString
(that kind of idea was suggested by Facebook).
For Instance from my server I can define in IOS app which feature or viewController should be used.(or On/Off them)
I searched all over Stack but still cant find an elegant way to implement what I want
Class myclass = NSClassFromString(className);
id obj = [[myclass alloc] init];
will work.
But I would like to call my custom init.
Class myclass = NSClassFromString(className);
id obj = [[myclass alloc] initWithCostumInitializer:userInfo];
I cant find a proper way to do it. Of course every time I receive an error because initWithCostumInitializer is not recognised.So I need to make the decision in run time.I believe I missing something.
Tnx a lot.
First off, you shouldn't get a compile-time error about an unknown method if the headers for the possible classe(s) are imported into the .m file where this code is running. Because of exactly this sort of dynamism, ObjC should let you get away with calling fairly arbitrary methods on objects of type id.
But that's just a bandaid solution. Really, if you know that that custom initializer method is present, then it's not an arbitrary class, right? You have some idea what kind of object it is, or at least what kind of base class it derives from, otherwise you wouldn't know to call that method. So you could always:
id customObj = [((BaseViewController *)[myclass alloc]) initWithCustumInitializer:userInfo];
If your error is a runtime error about the receiver missing that selector, then you have a real problem, which is: why are you calling a named method on an object that might not be the kind of object that has that method? If that's what's happening, you'll need to look at the class first to figure out what kind of thing you're actually about to create, and then behave appropriately for the init.
I am writing a class that will return an NSPredicate. I have written code like this:
constructedPredicate = [self predicateForSection:self.systemsSection];
I am wanting to keep the logic central to one method (other parts of the class call this same method and pass different properties), but my intuition is that it is a code smell / bad practice to call a method and pass a property into it. Is there a better pattern?
Nah; that is fine.
The property is a simple accessor. It just grabs the current state from the object.
The method computes a value based on a parameter.
This is exactly the delineation in functionality that properties were designed to address.
No, I don't see anything wrong with that at all.
Which from the following is the correct way of obtaining the meta class?
Class myMetaClass = objc_getMetaClass("NSString");
Or:
Class myMetaClass = object_getClass([NSString class]);
Are they both any different?
As mentioned in another post that is linked by the first answerer here:
Please tell me why objc_getMetaClass(); would break in certain cases in detail.
The proper way to use those in different scenarios.
Both functions are correct, but objc_getMetaClass("NSString") only works if NSString is registered with the objective C runtime. Which it almost always is if you want to get its metaclass.
But if you're creating a class using Class myClass = objc_allocateClassPair(superClass,"my_own_class",0) the situation is slightly different.
my_own_class isn't registered yet, so if you need to access the metaclass (in order to add class methods), you must use object_getClass(myClass).
objc_getMetaClass("my_own_class") would return nil.
The difference is, that the second function returns the object for the named class and the second first the object for the metaclass of the named class... :)
Both of them call the class handler callback if the class is not registered to check a second time. When you call the metaclass function you WILL get a return result.
...(However, every class definition must have a valid metaclass
definition, and so the metaclass definition is always returned,
whether it’s valid or not.)
from: Objective-C Runtime Reference
I think your real question is: What is the difference between a class and a metaclass ?
Please have a look at this excellent explanation:
What is meta-class in objective-c
This might be a silly question. I'm learning objective C (iOS) by studying the code and I came across the expression
[InstanceName class];
What does it do?
I tried to search for class method but It just pops up difference between class method and instance method etc. I guess it might give some sort of class object but I have no idea what is the purpose of the statement.
the original code is Sample Facebook App (scrumptious) using FB SDK....
If you see something like this as a standalone expression....
[InstanceName class];
... then the code is most likely forcing the execution of the +initialize method on said class. The first time any method is invoked on a class, the +initialize method will be invoked prior by the runtime. So, have a look at InstanceName and see if it has a +initialize method.
Note that forcing +initialize to execute in this fashion is a sure sign of bad design. +initialize should never need to be forced like this and should not have execution order dependencies.
There is a legitimate additional reason why this line of code might exist. By referring to InstanceName with a hard reference, it'll force the linker to link in all symbols in the library. (If you don't have a hard reference to at least one symbol in a library -- a .a -- some linkers will simply drop the library from the link unit entirely.)
It gets the class of the object.
So for instance if InstanceName is an instance of class Foo
[InstanceName class]; will return Foo, in a variable of type Class
You can use class_getClassName to get an NSString from this class to log it.
class is a method inherited from NSObject. It lets you get the instance of the class object representing the class of the instance on which the method is called.
It can be used to examine the metadata of the current object. For example, you can use class method to determine if a given object is of a particular class:
if ([sender isKindOfClass:[UIButton class]]) {
...
}
It returns the class of the object. Suppose you have an array of UIView subclasses you created and you want to perform some action only to those who belong to a certain class. You could loop through the array and check for each object's class:
for (id view in myViews) {
if ([view isKindOfClass:[MyUIViewSubclass class]]) {
// Do something
}
}
So I'm getting myself into a confusion over where my data's going and where it's stored in my application. It's not a specific question so hopefully someone can provide a generalised answer.
I need to pass some data around between a few UIViewController instances, and I'm currently doing that with a singleton object called my dataManager. This class has one method, a class method, called + (LCDataManager *) sharedDataManager, and that method basically checks if whether the sharedDataManager already exists, if so, return it, if not, create it and set up its variables. This means that I can refer to that class anywhere I like, access and modify its variables anywhere I like, from across multiple classes.
First question: is this the correct / best / most appropriate means of passing data around like this? I'm hoping it obeys MVC, it feels like it does, and I hope I'm right.
Second question: what if I want to put an instance method in that class, and call it from within the class method? Let's say my sharedDataManager needs to call a method to grab some objects one of its variables (an array), and put them in another array, then send that back out again. I can't do that, can I? What's the way around that? If I make an instance of that class (rather than using the shared instance), I lose the ability to use that instance across multiple viewControllers.
I'm hideously confused, and it seems like it's not the problem I'm making it. Appreciate any guidance, and preferably not that "Read the Apple documentation" stuff – they write as if you already know what you're doing, and frankly I don't yet.
First question: is this the correct / best / most appropriate means of passing data around like this? I'm hoping it obeys MVC, it feels like it does, and I hope I'm right.
Your design is perfectly MVC compliant.
Second question: what if I want to put an instance method in that class, and call it from within the class method?
you can surely define an instance method and call it like this:
[[MyModelClass sharedModel] myInstanceMethod];
indeed, [MyModelClass sharedModel] will give you an instance of MyModelClass (which should be guaranted to be unique being it a singleton).
If you want to call the instance method from the sharedModel class method, you could also do that, because sharedModel owns a reference to your singleton, so it can send messages to it.
is this the correct / best / most appropriate means of passing data around like this?
There's nothing wrong with only having a single instance of LCDataManager, but using the Singleton pattern has potential problems. An alternative is to just initialize one LCDataManger and to pass it around to wherever it's needed.
what if I want to put an instance method in that class, and call it from within the class method?
The accessor + (LCDataManager *) sharedDataManager should only return the instance. I guess what you want is something like
+ (LCDataManager *)preparedDataManager {
LCDataManager *shared = [self sharedDataManager];
[shared doSomeInstanceMagic];
return shared;
}
- (void)doSomeInstanceMagic {
// magic!
// grab some objects one of its variables (an array),
// and put them in another array
}
Matthijs Hollemans has an excellent three-part tutorial on his blog about the correct way to make your view controllers talk to each other:
Part 1
Part 2
Part 3
there is no problem with this development architecture, and it is the must used (I think) in the iOS development. In the book IOS Programming: The Big Nerd Ranch Guide they call it Model View Controller Store.
Regarding your second question, yes, you can declare instance methods and call then from your sharedDataManager. What is not usual is creating other instances of a singleton class, but it is possible.