Question

I’m doing some Interop from Mono C# to Obj-C and ran into this problem.
The C# code needs to pass a callback – which it does with a function pointer.
I can get the function pointer from the Obj-C side and call it and everything works.
But I now need to give that function pointer as a callback to third party API which works with blocks as a callback.
I want the third party to call the C# function – so in a way i’m trying to either convert the function pointer to a block so the third party can run it, or make some sort of a bridge – create my own block that runs that function pointer and give it to the third party. I can’t seem to find a way to do that – how would I generate a block with info of which function to run and then give it to the third party.
Maybe there’s another option for me?

Edit: Putting the function in a global variable might work but I want to be able to have a multitude of those as the third party API is asynchronous and I don’t want it calling the wrong callback.

Code I tried :

typedef void (*DummyAction)(char * result);
typedef void (^DummyBlock)(char * result);

@interface FunctionToBlock : NSObject
{
    DummyAction function;
    DummyBlock block;
}

- (id) initWithFunction: (DummyAction) func;
- (DummyBlock) block;
@end

@implementation FunctionToBlock : NSObject
- (id) initWithFunction: (DummyAction) func {
    if (self = [super init]) {
        function = func;
        block = ^(char * result) {
            function(result);
        };
    }
    return self;
}

- (DummyBlock) block {
    return block;
}
@end

And then I run this with

void RegisterCallback( char * text, DummyAction callback)
{
    FunctionToBlock *funcToBlock = [[FunctionToBlock alloc] initWithFunction : callback];
    funcToBlock.block(text);
}

And it fails with BAD_ACCESS. Maybe i’m doing something wrong as i’m not very proficient with Obj-C yet. I can confirm that the callback is ok if run directly and that the block is being called but it fails on the function(result) line.

Answer 1

why not just have a simple function

typedef void (*DummyAction)(char * result);
typedef void (^DummyBlock)(char * result);

DummyBlock functionToBlock(DummyAction func) {
    return [[^(char * result) {
                 func(result);
             } copy] autorelease];
}