CODEWITHSUNDEEP
objective-cmacrosswift
atxe
atxe

Reputation: 5079

How to use a Objective-C #define from Swift

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

Upvotes: 78

Views: 109409

Answers (5)

Joshua
Joshua

Reputation: 221

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 }
}

Upvotes: 22

garg
garg

Reputation: 2727

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 {

}

Upvotes: -1

Amr Angry
Amr Angry

Reputation: 3831

simple swift language don't need an macros all #define directives. will be let and complex macros should convert to be func

Upvotes: 1

fabrice truillot de chambrier
fabrice truillot de chambrier

Reputation: 5558

At the moment, some #defines 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 #defines to actual constants, which is better than #defines 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.

Upvotes: 66

Ankish Jain
Ankish Jain

Reputation: 11361

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)
 }

Upvotes: 8

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