We have an Objective C library that creates objects that are meant to be used in Swift code.
The function returns the object as an id. This is the declaration in Objective C header file (Clazz.h). The header file has been exposed in bridging header as required for interoperability.
+ (id)getObject;
The pointer returned is an instance of AVAssetWriter*. To access this API in Swift, I followed the steps in below post:
Objective-C pointer and swift
This is the Swift 3 code consumer code:
let obj = (Clazz.getObject() as! UnsafeMutableRawPointer).assumingMemoryBoundTo(to: AVAssetWriter.self).pointee
It built fine. However, when this code executes, the app seems to crash.
In Clazz.h, I declared the function as:
+ (AVAssetWriter*)getObject();
and tried to use it in Swift as,
let obj = Clazz.getObject() as AVAssetWriter
Code built fine but it failed when it was executed.
How do we access Objective C created objects in Swift?
Please note that I was able to inspect the value in swift code and the problem is not in bridging. Also, the memory location is not dangling.
By declaring obj variable as below, things worked
let obj:AVAssetWriter = Clazz.getObject() as AVAssetWriter
Related
I am migrating my project from ObjC to Swift. I have this code:
const char *specific = "my_queue"
dispatch_queue_set_specific(myQueue, specific, (void *)specific, NULL);
Later in my unit test, I have:
assertTrue(dispatch_get_specific(specific))
I noticed that in Swift, the API has changed, and we can't use any key type anymore
let value = String(cString: specific, encoding: .utf8)
myQueue.setSpecific(DispatchSpecificKey<String>(), value)
The 2 APIs already diverged. In ObjC, key and values are both c strings; but in Swift the key is a special type DispatchSpecificKey which is not available in ObjC.
So how can I set the specific in Swift, and get the correct specific from ObjC?
Another way around seems problematic too: how can I set the specific in ObjC, and get the correct specific from Swift?
I'm using NSURLSession to connect to a database. I have this already implemented in C++ for Windows and am trying to get it working on iOS also. I have a .h file derived from a base C++ class that is the header for my .mm file. If I'm correct I have to implement all the functions in my .h file in C++. However NSURLSession is an Objective-C function. How do I call an Objective-C method from my C++ function?
I have a C++ function called Connect() where I make a C++ object m_Delegate that has an alloc and init.
this->m_Delegate = [[PrivateNSURLSessionDelegate alloc] initWihParent:this];
//where PrivateNSURLSessionDelegate is the name of my interface.
That interface has -(bool)NSConnect (with implementation in the #implementation) which I'm trying to call from:
void Connect()
{
[PrivateNSURLSessionDelegate NSConnect];
//This however gives me the error: +[PrivateNSRLSessionDelegate NSConnect]: unrecongnized selector sent to class
}
I also tried it using my C++ object
void Connect()
{
[m_Delegate NSConnect];
//This gives me a error that is unrecognized selector sent to instance
}
Is there a better way to do this? I basically want to ask the Objective-C to do all the NSURL stuff and send just the data back to the C++.
I'm completely new to Objective-C so any and all help would be greatly appreciated! Thanks!
-(bool)NSConnect
Here the - indicates it is an instance method. Conversely + would indicate a class method.
That being said, [PrivateNSURLSessionDelegate NSConnect]; calls a class method, since you call it on the interface PrivateNSURLSessionDelegate.
However, this is not defined as it is defined as NSConnect is defined as an instance method (btw the convention is that (instance) methods always start with a lowercase).
[m_Delegate NSConnect];
Does however call the instance method. You should define -(bool)NSConnect in the header file of PrivateNSURLSessionDelegate, not above the #implementation in the implementation file, that makes in a private method and thus inaccessible.
There is Objective-C, which is a superset of C, and Objective-C++, which is a superset of C++. Objective-C++ source code files have a .mm suffix, where Objective-C would have a .m suffix.
You cannot call Objective-C from C++. You can however call Objective-C from Objective-C++, and you can write your usual C++ classes in Objective-C++ as well.
I am importing my Objective C classes in a bridging header file into Swift:
Bridging Header
#import "MyCustomClass.h"
In my swift class, I am trying to use this code:
var x = MyCustomClass()
x.myFunMethod()
However, before I run/build I get "Use of unresolved identifier" errors at the above two lines. Furthermore, I cannot use autocomplete to type out x.myFunMethod(). Once I run/build, the errors go away and the app runs as normal.
I'm using an Objective-C class in my Swift project via a bridging header. The method signature looks something like this:
- (CFArrayRef)someMethod:(someType)someParameter;
I started by getting an instance of the class, calling the method, and storing the value:
var myInstance = MyClassWithThatMethod();
var cfArr = myInstance.someMethod(someValue);
Then try to get a value in the array:
var valueInArrayThatIWant = CFArrayGetValueAtIndex(cfArr, 0);
However I get the error Unmanaged<CFArray>' is not identical to 'CFArray'. What does Unmanaged<CFArray> even mean?
I looked through How to convert CFArray to Swift Array? but I don't need to convert the array to a swift array (however that would be nice). I just need to be able to get values from the array.
I have also tried the method of passing the CFArray into a function outlined in this answer:
func doSomeStuffOnArray(myArray: NSArray) {
}
However I get a similar error when using it:
doSomeStuffOnArray(cfArr); // Unmanaged<CFArray>' is not identical to 'NSArray'
I am using CFArray because I need to store an array of CGPathRef, which cannot be stored in NSArray.
So how am I supposed to use CFArray in Swift?
As explained in
Working with Core Foundation Types, there are two possible solutions when
you return a Core Foundation object from your own function that is imported in Swift:
Annotate the function with CF_RETURNS_RETAINED or CF_RETURNS_NOT_RETAINED.
In your case:
- (CFArrayRef)someMethod:(someType)someParameter CF_RETURNS_NOT_RETAINED;
Or convert the unmanaged object to a memory managed object with takeUnretainedValue() or takeRetainedValue() in Swift. In your case:
var cfArr = myInstance.someMethod(someValue).takeUnretainedValue()
An Unmanaged is a wrapper for an actual CF value. (Sort of like an optional.) It's there because ARC can't tell from looking at the declaration of someMethod: whether that method retains the value it returns.
You unwrap an Unmanaged by telling ARC what memory management policy to use for the value inside. If someMethod calls CFRetain on its return value:
let cfArr = myInstance.someMethod(someValue).takeRetainedValue()
If it doesn't:
let cfArr = myInstance.someMethod(someValue).takeUnretainedValue()
After you do that, cfArr is a CFArray, so you can use the bridging tricks from the other questions you linked to for accessing it like a Swift array.
If you own the code for someMethod you can change it a bit to not need this. There's a couple of options for that:
Annotate with CF_RETURNS_RETAINED or CF_RETURNS_NOT_RETAINED to tell the compiler what memory behavior is needed
Since it's an ObjC method, bridge to NSArray and return that--it'll automatically become an [AnyObject] array in Swift.
I am in the process of migrating my streaming audio engine to swift. i am finding it difficult to use the C Audio API in swift.
I have a problem with AudioFileStreamOpen api where it takes 2 C functions as a parameter. I don't know how to use this API is swift.
AudioFileStreamOpen(self as UnsafePointer<()>, propertyProc, packetProc, kAudioFileMP3Type, audioStreamId)
I have defined the callback method as below for this API. But i am getting the compilation error.
func propertyProc(inClientData: UnsafePointer<()>,inFileStreamId: AudioFileStreamID,inPropertyId: AudioFileStreamPropertyID,ioFlags: UnsafePointer<UInt32>) -> Void {
.....
}
func packetProc(inClientData: UnsafePointer<()>,inNumberOfBytes: UInt32,inNumberOfPackets: UInt32, ConstUnsafePointer<()>, inPacketDescriptions: UnsafePointer<AudioStreamPacketDescription>) -> Void {
.....
}
Any help is appreciated to correctly define this C API in swift
You can't (currently) use an API requiring a C callback pointer from pure Swift code. Calling Swift functions or methods using a C function pointer is not supported by the current beta 4 language implementation, according to replies in the Swift forum at devforums.apple.com
UPDATE: The above answer is obsolete as of Swift 2.0
One alternative is to put some small trampoline C callback functions in an Objective C file, which can interoperate with Swift, and have those C functions in turn call a block or closure, which can be in Swift code. Configure the C callbacks with your Swift closures, and then pass those C callbacks to the CoreAudio functions.
I don't know much about Audio API, however, you should replace UnsafePointer by a pointer to an Object. for example:
var clientData : AnyObject?
var listenerProc : AudioFileStream_PropertyListenerProc = AudioFileStream_PropertyListenerProc.convertFromNilLiteral()
var packetsProc : AudioFileStream_PacketsProc = AudioFileStream_PacketsProc.convertFromNilLiteral()
var audioFileTypyeId : AudioFileTypeID = 0
AudioFileStreamOpen(&clientData, listenerProc, packetsProc, audioFileTypyeId, &streamId)
the initialization code for listenerProc, packetsProc or other variables is just to by-pass the compiler error.
To your situation, try to replace 'self as UnsafePointer<>' by '&self'. However 'self' must be something that can be converted to compatible data type.
https://developer.apple.com/library/prerelease/ios/documentation/MusicAudio/Reference/AudioStreamReference/index.html#//apple_ref/c/func/AudioFileStreamOpen