Use an ObjC Block as a callback for CGDataProviderCreateWithData

Question

We want to call CGDataProviderCreateWithData() with the releaseData callback defined right in the arguments list. How can we do it?

I've tried a bunch of options, but was unable to crack the block syntax for this case.

The following:

const CGDataProviderRef provider = CGDataProviderCreateWithData(
    NULL,
    outputPixelDataBytes,
    pixelsSize,
    ^void(void * __nullable info, const void * data, size_t size) {
        free(data);
    });

doesn't compile with the error:

Passing 'void (^)(void * _Nullable, const void , size_t)' to parameter of incompatible type 'CGDataProviderReleaseDataCallback _Nullable' (aka 'void ()(void * _Nullable, const void * _Nonnull, unsigned long)')

Not sure what to change to get rid of the error.

Answer 1

CGDataProviderCreateWithData() does not take a block, it takes a function pointer, which is a different type of thing. You can't define a function inline like you're trying to do. You will have to define the function out-of-line and pass its address:

static void MyReleaseCallback(void * __nullable info, const void *  data, size_t size)
{
    free(data);
}

...
{
    ...
    const CGDataProviderRef provider = CGDataProviderCreateWithData(
        NULL,
        outputPixelDataBytes,
        pixelsSize,
        MyReleaseCallback);
    ...
}