Passing a swift function as a parameter in objective-c

Question

I have a swift class, A, which accepts delegates. I have another swift class, B, which implements the delegates. Now the object of A is instantiated from objective-c code.

I need to pass the function g as a parameter to the function f. How do I do this ?

Class which accepts a delegate :

class A {
    func f(_ e: String, d D: @escaping ((String)->Void)) {
        D() // Call the function that we recieved as a parameter
    }
}

Class which implements the delegate :

class B {
    func g(_ m: String) {
        // Implementation.
    }
}

How things are called from obj-c :

A *a;
B *b;

[a f:@"someString" d:b.g] // How to pass the swift function as a parameter ?

It looks like closure and it will be treat as block in Obj c — Prashant Tukadiya
– Prashant Tukadiya, Commented Nov 24, 2017 at 8:07
@Cy-4AH I don't know how to do that. I am a newbie in swift and obj-c. — Rohith R
– Rohith R, Commented Nov 24, 2017 at 8:13

clemens · Accepted Answer · 2017-11-24 08:35:21Z

1

You should encapsulate the call to g into a Objective-C block like this:

[a f:@"someString" d:^(NSString *s) {
    [b g:s];
}];

If you also want keeping the parameter function for d variable, you need a dictionary of closures:

A *a = ...;
B *b = ...;
NSDictionary *myFunctions = @{
    'g': ^(NSString *s) { [b g:s]; },
    'h': ^(NSString *s) { [b h:s]; }
};
NSString *functionName = ...;

[a f:@"someString" d:myFunctions[functionName]];

edited Nov 24, 2017 at 8:35

answered Nov 24, 2017 at 8:24

clemens

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2 Comments

Rohith R Over a year ago

I am not trying to call g. I am trying to pass the function g as a parameter to f.

clemens Over a year ago

Yes, I understood this but you can't create a Swift-like function from an Objective-C method directly. The closure eliminates this problem. My code doesn't call g. It creates a closure to call g.

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