Question

I am seriously confused about the Objective-C #import.

I searched and found several tutorials saying that if I have lots of constraints like

#define val1 
#define val100

it’s better to put all constraints in one file and import this file for reusing all values.

But i am still confused, I saw many code samples which #import all other files’ headers in which there is is no

#define constraints 

These two files are normal UIViewControllers, but their headers are imported.

#import viewcontroler1.h 
#import viewcontroler2.h 

1. When can we simply create objects of classes why import them?
2. Where to import files in .h or .m?
3. What to import, the .h or the .m file in Objective-C?

I am seriously confused, please help me.

Answer 1

I’m not sure I’m really understanding what you’re asking for, but you should avoid importing header files in other header files, if you don’t need to. Instead, #import the headers you need in the .m file and use the @classdirective in your .h files instead.

From the Apple docs:

The @class directive minimizes the amount of code seen by the compiler
and linker, and is therefore the simplest way to give a forward
declaration of a class name. Being simple, it avoids potential
problems that may come with importing files that import still other
files. For example, if one class declares a statically typed instance
variable of another class, and their two interface files import each
other, neither class may compile correctly.

Otherwise, you might be exposing your imported variables to more classes than you actually need. If you’re importing your constants.h in viewcontroler1.h, any other class importing viewcontroler1.h will also have constants.h. Sometimes this might be what you need, but it usually isn’t.

Hope that helped in some aspect…