under Active Compilation Conditions i have added a new flag (for debug only) called SOMEFLAG.
the check is implemented like so and works great:
#if SOMEFLAG
print("SOMEFLAG is true");
#endif
it actually prints like i would expect. now, i need to examine the same flag from Objective-C class and it never evaluates to true. any idea why?
should i make this flag in other way?
in general my goal is to be able to detect when it is executed from another target, the build is triggered from the cli.
if there is other way that less limiting i would like to know.
thanks!
In Objective-C (and other C-like languages that use a preprocessor) the canonical way to check whether a symbol is defined would be using #ifdef, not #if. There is an #if directive in Objective-C, but it doesn't behave quite the same way as the Swift #if compiler directive.
Swift 2 have API availability checking.
The compiler will give you an error when using an API too new for your
minimum target OS
Why can't the objective-c compiler do the equivalent?
I googled objective c API availability checking and only swift 2 results came out so I assume the compiler for objective c can't do that.
Xcode 9.0 brings the runtime availability checking syntax from Swift to Objective-C:
if (#available(macOS 10.9, *))
{
// call 10.9+ API
}
else
{
// fallback code
}
this comes complete with warnings for calling APIs that are newer than your deployment target (if those calls are not wrapped in checks).
finally ;)
The warning (Swift makes it an error) just hadn't been implemented in the Clang compiler for years, but it's not an inherent Objective-C limitation (although due to its dynamic nature, you won't be able to catch all cases), nor Swift terminology.
The Apple macros (e.g., NS_CLASS_AVAILABLE) and source attributes (__attribute__((visibility(...))), __attribute__((availability(...)))) to annotate headers with availability information have been there for years, and they are widely-used in Apple's SDKs. The macros are defined in Foundation's NSObjCRuntime.h, and the Availability.h/AvailabilityMacros.h system headers, and the compiler can (and does) read them.
In early 2015, the -Wpartial-availability warning has been added to Clang's master branch, but this commit/warning hadn't made its way into Apple's version of Clang until (including) Xcode 7.2. You will get an unknown warning option log when adding the warning flag to a project in Xcode 7.2, but the flag is available in Xcode 7.3. There's currently no predefined setting for it, but you can add the flag to Other Warning Flags under Build Settings.
There are other tools that use LLVM libraries to detect partially available APIs, e.g., Deploymate. For my diploma thesis, I developed a tool that integrates directly into Xcode and is based on a modification to the Clang compiler. The code is still online, but I haven't kept up with the general Clang development so it won't be of much use, except for learning purposes. However, the "official" code (linked above) is much cleaner and better.
Edit: Starting with Xcode 9, availability checking will work for Objective-C (and C), too. Instead of using the above-mentioned warning flag, which does not support raising the deployment target temporarily/locally and therefore causes plenty of false positives, there's -Wunguarded-availability, and if (#available(iOS 11, *)) {...} to check and raise the deployment target for the following block of code. It is off by default, but -Wunguarded-availability-new will be on by default, and starts checking anything beyond iOS/tvOS 11, watchOS 4, and High Sierra. More details on that can be found in the Xcode 9 beta release notes, which currently requires signing in with a developer account.
Objective C does not have availability checking as part of the language, as the same result is available via Objective C preprocessor.
That is the "traditional" way of doing that in C derived languages.
Want to know if compiled in debug mode?
#ifdef DEBUG
// code which will be inserted only if compiled in debug mode
#endif
Want to check at compile time for a minimum version?
Use the Availability.h header in iOS, and similar headers for Mac OS X.
This file reside in the /usr/include directory.
just test __IPHONE_OS_VERSION_MAX_ALLOWED with the preprocessor, e.g.:
#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 80000
if ([application respondsToSelector:#selector(registerUserNotificationSettings:)]) {
[[UIApplication sharedApplication] registerUserNotificationSettings:[UIUserNotificationSettings settingsForTypes:(UIUserNotificationTypeBadge|UIUserNotificationTypeSound|UIUserNotificationTypeAlert) categories:nil]];
}else{
[[UIApplication sharedApplication] registerForRemoteNotificationTypes: (UIUserNotificationTypeBadge|UIUserNotificationTypeSound|UIUserNotificationTypeAlert)];
}
#else
[[UIApplication sharedApplication] registerUserNotificationSettings: (UIUserNotificationTypeBadge|UIUserNotificationTypeSound|UIUserNotificationTypeAlert)];
#endif
As Swift does not have a preprocessor, they had to invent a way of doing these kind of checks within the language itself.
If you want to check availability of a method at runtime, please notice that the appropriate way is by using the method respondsToSelector:, or instancesRespondToSelector: (the latter at class level).
You will normally want to combine both approaches, compile time conditional compilation and runtime check.
Objective C method presence verification, e.g. at class level:
if ([UIImagePickerController instancesRespondToSelector:
#selector (availableCaptureModesForCameraDevice:)]) {
// Method is available for use.
// Your code can check if video capture is available and,
// if it is, offer that option.
} else {
// Method is not available.
// Alternate code to use only still image capture.
}
If you want to test if a C function exists at runtime, it is even simpler: if it exists, the function itself it is not null.
You can't use the same identical approach in both languages.
It does these days. Furthermore, with Xcode 11 (including the current Xcode 11.3.1), you can even get it from the snippets. Press the + button towards the top right of Xcode (as shown in the image below).
Then in the search box, type "API". All 3 versions of the snippet for API Availability Check will appear -- Objective C, C and Swift.
Of course, you will get errors in Objective-C code. But you won't find results in google for Objective-C, if you use a term defined for Swift as you will not find kisuaheli website in google if you search for a german word. ;-)
You will get an error linking Objective-C code against a too old SDK. This is simply because the used method or class or $whatever is not defined in the header for that SDK. Again, of course.
This is typical Swift marketing of Apple: Because of the incapability of Swift they have to extend the language to get something, which is quite easy in Objective-C. Instead of clarifying that this is the result of the poorness of Swift, they tell you that this is a great feature of Swift. It is like cutting your fingers and then saying: "We have the great plaster feature!!!!!!!!" And you have to wait only some days and one comes around on SO with the Q: "Why does Objective-C does not have the great plaster feature???????" The simple answer: It does not cut your fingers.
The problem is not to generate the errors. The problem is to have one source code for all versions, so you can simply change the SDK version and get new code (or errors). You need that for easier maintenance.
In Objective-C you simply can use the answer found here:
Conditionally Hide Code from the Compiler or you can do that at runtime as mentioned in the comments to the Q. (But this is a different solution of the problem by nature, because it a dynamic approach instead of a static one as you have to do in Swift.)
The reason for having a language feature in Swift is that Swift has no preprocessor, so the Objective-C solution would not work in Swift. Therefore conditional code would be impossible in Swift and they had to add the plaster, eh, language feature.
I'm working on a library and I would like to support both memory management approaches (ARC and MRR) in one codebase.
I don't want to force users to use special flags for my code (-fobjc-arc).
I know about the preprocessor test: #if __has_feature(objc_arc), but what is the best practice to use that to cover the all differences?
Does anyone have any experience with that to make it clean and easy to work with?
The preferable way would be to use some macros for translations between ARC and non-ARC, which I can use in my code.
=========
My problem was solved by the accepted answer, but as a tip for others, I found a blog post by John Blanco giving the best set of examples for how to handle my problem.
Refer the code of MBProgressHUD in github. I think, that's what you want.
#if __has_feature(objc_arc)
#define MB_AUTORELEASE(exp) exp
#define MB_RELEASE(exp) exp
#define MB_RETAIN(exp) exp
#else
#define MB_AUTORELEASE(exp) [exp autorelease]
#define MB_RELEASE(exp) [exp release]
#define MB_RETAIN(exp) [exp retain]
#endif
This is how they are using these macros
self.indicator = MB_AUTORELEASE([[MBRoundProgressView alloc] init]);
Either use ARC and instruct people who will use the code to set compilation flags per file (-fobjc-arc), and force them to do so by adding this to the header:
#if !__has_feature(objc_arc)
#error ARC must be enabled!
#endif
Or build as lib/framework with ARC enabled. Wrapping memory management code in preprocessor directives is a terrible idea.
One way to support both ARC and Non-ARC code is to go to the Target, Build Phases, and to the Compile Sources section.
From there you should see all your .m files. You can then add to any file -fno-objc-arc under the Compiler Flags to tell the compiler to ignore ARC.
Yeah, don't do this. You'll end up having to test your code fully twice for every change. And debugging everything twice. It isn't worth the effort.
You really really want to write your code purely ARC or purely non-ARC.
There are very few constructs that can appear in a header file that won't work in one or the other.
I'm trying to build a library that has convenience methods for dealing with the iOS and OSX AddressBook frameworks (Contact List on iOS and Contacts on OSX) and includes such methods as:
(BOOL)addressBookContainsRecordWithID:(NSString *)recordID (NSInteger in the case of OSX)
(id)newOrExistingGroupWithName:(NSString *)groupName
(id)addressBookRecordWithID:(NSString *)recordID
etc.
And I'd like to be able to call these methods on both OSX and iOS, but have that method execute the logic path respective for each device. For example, on OSX it would use a method that uses ABPerson and ABGroup whereas on iOS it would use a method that uses ABRecordRef.
My current plan is to have preprocessor directives (#if device-is-osx callOSXMethod #else callIOSMethod) which figure out whether I'm using iOS or OSX and use the correct method.
Is there a better way I could go about this? I feel like there is some design patter that could be used here.
It depends on how much shared code there will be between your two different implementations. If almost all of the code is shared except for a few specific method calls to the AddressBook frameworks then preprocessor directives with #if TARGET_OS_IPHONE are the way to go.
On the other hand, if you find that the code in your #if blocks is getting quite long, it usually makes more sense to split the Mac and iOS implementations into separate files that share an identical interface. Thus you'd have:
MyAddressBook.h - Shared by both
MyAddressBook_Mac.h - Mac implementation of MyAddressBook
MyAddressBook_iOS.h - iOS implementation of MyAddressBook
This is made easier by the fact that your implementations can even have different instance variables by using a class extension inside each implementation file. This second pattern leads to greater readability at the cost of having to maintain whatever common code there is in two places.
Preprocessor directives are the way to go. There are even predefined ones you can use:
#if TARGET_OS_IPHONE
// iOS code here
#else
// OS X code here
#endif
As far as I understand when you use properties the compiler still converts them to accessor methods during compilation. I got a little irritated when I read you need OSX 10.5 or later to use properties. Why is that so?
If in the compiled application are in fact still accessor methods I see no need for OSX 10.5. Or is there something else going on during run-time?
Because the Objective-C 2.0 runtime was not back ported to 10.4. You need compiler and runtime support to handle all of ObjC 2.0 properly.