How to use a Objective-C #define from Swift
Objective CMacrosSwiftObjective C Problem Overview
I am migrating a UIViewController
class to train a bit with Swift. I am successfully using Objective-C code via the bridging header but I have the need of importing a constants file that contains #define
directives.
I have seen in Using Swift with Cocoa and Objective-C (Simple macros) the following:
> Simple Macros
>
> Where you typically used the #define
directive to define a primitive constant in C and Objective-C, in Swift you use a global constant instead. For example, the constant definition #define FADE_ANIMATION_DURATION 0.35
can be better expressed in Swift with let FADE_ANIMATION_DURATION = 0.35
. Because simple constant-like macros map directly to Swift global variables, the compiler automatically imports simple macros defined in C and Objective-C source files.
So, it seems it's possible. I have imported the file containing my constants into the bridging header, but I have no visibility from my .swift
file, cannot be resolved.
What should I do to make my constants visible to Swift?
UPDATE:
It seems working with NSString
constants, but not with booleans:
#define kSTRING_CONSTANT @"a_string_constant" // resolved from swift
#define kBOOL_CONSTANT YES // unresolved from swift
Objective C Solutions
Solution 1 - Objective C
At the moment, some #define
s are converted and some aren't. More specifically:
#define A 1
...becomes:
var A: CInt { get }
Or:
#define B @"b"
...becomes:
var B: String { get }
Unfortunately, YES
and NO
aren't recognized and converted on the fly by the Swift compiler.
I suggest you convert your #define
s to actual constants, which is better than #define
s anyway.
.h:
extern NSString* const kSTRING_CONSTANT;
extern const BOOL kBOOL_CONSTANT;
.m
NSString* const kSTRING_CONSTANT = @"a_string_constant";
const BOOL kBOOL_CONSTANT = YES;
And then Swift will see:
var kSTRING_CONSTANT: NSString!
var kBOOL_CONSTANT: ObjCBool
Another option would be to change your BOOL
defines to
#define kBOOL_CONSTANT 1
Faster. But not as good as actual constants.
Solution 2 - Objective C
Just a quick clarification on a few things from above.
Swift Constant are expressed using the keywordlet
For Example:
let kStringConstant:String = "a_string_constant"
Also, only in a protocol definition can you use { get }
, example:
protocol MyExampleProtocol {
var B:String { get }
}
Solution 3 - Objective C
In swift you can declare an enum, variable or function outside of any class or function and it will be available in all your classes (globally)(without the need to import a specific file).
import Foundation
import MapKit
let kStringConstant:String = "monitoredRegions"
class UserLocationData : NSObject {
class func getAllMonitoredRegions()->[String]{
defaults.dictionaryForKey(kStringConstant)
}
Solution 4 - Objective C
simple swift language don't need an macros all #define directives. will be let and complex macros should convert to be func
Solution 5 - Objective C
The alternative for macro can be global variable . We can declare global variable outside the class and access those without using class. Please find example below
import Foundation
let BASE_URL = "www.google.com"
class test {
}