使用ARC不允许使用指向'CFReadStreamRef *'的Objective-C指针的间接指针

Question

I want to use CFStreamCreatePairWithSocketToHost with NSInput - and OutputStream s. I have two ivars NSInputStream *_inputStream and NSOutputStream *_outputStream .

The following gives me two error messages:

CFStreamCreatePairWithSocketToHost(NULL,
  (__bridge_retained CFStringRef)self.hostname, self.port,
  (CFReadStreamRef *)&_inputStream, (CFWriteStreamRef *)&_outputStream);

error: cast of an indirect pointer to an Objective-C pointer to ' CFReadStreamRef * ' (aka ' struct __CFReadStream ** ') is disallowed with ARC
error: cast of an indirect pointer to an Objective-C pointer to ' CFWriteStreamRef * ' (aka ' struct __CFWriteStream ** ') is disallowed with ARC

How would I fix this? I tried using __bridge but I got similar error messages.

Answer 1

Pass a pointer to actual CFReadStreamRef and CFWriteStreamRef variables, then cast when assigning to your NSTypes. Basically:

CFThingRef cfThing = NULL;
CFFunctionGetThing(&cfThing);
NSThing * nsThing = cfThing;

Of course, you'll have to add the appropriate bridge cast and do all appropriate reference count ops for cfThing .

Answer 2

Think about what ARC is doing, and what __bridge casts do: ARC takes responsibility for retaining / releasing NSObjects. __bridge casts transfer that responsibility. For example, __bridge_retained retains an NSString, cast the pointer to CFStringRef, and handed the responsibility for doing the matching release operation to whoever uses the CFStringRef.

That cannot possibly work with a pointer to an NSObject* or a pointer to a Core Foundation ref. A pointer points to a memory location. Any kind of NSObject* or Core Foundation object could be stored there.

You need two variables, one for an NSInputStream* and one for a CFReadStreamRef. Use the appropriate bridge cast to move the NSInputStream* to the CFReadStreamRef. Now you have what you want, and can pass the address on.