Objective C - Dynamically compile or do not compile class and codes - ios

Question

First of all; I don't know if this question is duplicate or not. Because I don't know how to search for this question.
Let me explain my question with scenario.
I've iOS 11 Project (Deployment target 9.2). Let's call it Master.
I've coded 2 POD Projects and Master project has reference for them.
POD1 has classes A.class B.class and C.class
POD2 has classes D.class E.class and F.class
Master project is using both POD1 and POD2
Here is the question; What if I want to remove POD1 reference and want to distribute project with just POD2?
I have to remove all codes inside Master which using POD1? I don't think so... It is very amateur way to do it. And there should be professional way to do it.
Maybe Run Script?
or
Maybe putting some flags inside code where using POD1 classes to exclude from build? So I don't get error as File Not Found..
I know the way using
#ifndef HIDE_<insert name here>
CODE
#endif
But don't think it's a correct way to do it..
Any ideas & suggestions are welcome.
Thank you.

Answer 1

Using Objective-C categories, you can conditionally compile groups of methods for different targets. Here's an example.
Let's say you have two targets that both use a class A. In one target (a background daemon) you need just the core functionality of class A. In the GUI version of your app you need the same functionality plus additional methods to support the user interface. The problem is that you can't simply compile all of class A in the daemon target because it will reference Cocoa classes that the daemon target doesn't get linked to. You need to isolate the user interface code and compile/link it only in the target that uses it. Here's how:
Base classes
A.h
#interface A : NSObject
#property NSUInteger someProperty;
- (void)doSomething;
#end
A.m
#implementation A
- (void)doSomething
{
// Do something useful
}
#end
Now define the GUI specific methods in a category:
A+ViewAdditions.h
#interface A (ViewAdditions)
#property (readonly,nonatomic) NSView* view;
#end
A+ViewAdditions.m
#implementation A (ViewAdditions)
- (NSView*)view
{
// Create a view that will display this object
NSView* view = [[NSView alloc] initWithFrame:NSZeroRect];
return view;
}
#end
In both targets, you include/compile the A.m module, so both targets compile the core class A which includes its someProperty and doSomething method. But in your GUI target, you also compile the A+ViewAdditions.m module. In your GUI app, the A class has a view property, but in your daemon it will not. You can test for this at runtime:
A* a = [A new];
if ([a respondsToSelector:#selector(view)])
NSLog(#"a.view is a %#",a.view.className); // prints "is a NSView"
else
NSLog(#"a has no view property");
This can be extended to subclasses:
B.h
#interface B : A
#end
B.m
#implementation B
#end
B+ViewAdditions.h
#interface B (ViewAdditions)
#end
B+ViewAdditions.m
#implementation B (ViewAdditions)
- (NSView*)view
{
NSTextField* fieldView = [[NSTextField alloc] initWithFrame:NSZeroRect];
return fieldView;
}
#end
And...
A* a = [A new];
B* b = [B new];
if ([a respondsToSelector:#selector(view)])
NSLog(#"a.view is a %#",a.view.className); // prints "is a NSView"
if ([b respondsToSelector:#selector(view)])
NSLog(#"b.view is a %#",b.view.className); // prints "is a NSTextField"
There are limitations to categories, which you should be aware of. The most problematic is that you can't add instance variables or stored properties to a class via a category. But category methods can access private variables in the class, and I'll sometimes define private ivars in the base class that only get used by the category. Your style may vary.