Hybrid programming in Apple system development (2): mutual calls between Swift and C, system development swift

Hybrid programming in Apple system development (2): mutual calls between Swift and C, system development swift
When performing mutual calls between Swift and C, it is necessary to first understand the type conversion relationship between the two languages:

C type	Swift type
Bool	CBool
Char, signed char	CChar
Unsigned char	CUnsignedChar
Short	CShort
Unsigned short	CUnsignedShort
Int	CInt
Unsigned int	CUnsignedInt
Long	CLong
Unsigned long	CUnsignedLong
Long	CLongLong
Unsigned long	CUnsignedLongLong
Wchar_t	CWideChar
Char16_t	CChar16
Char32_t	CChar32
Float	CFloat
Double	CDouble

Next, I will demonstrate how to call the C method in Swift and create a Swift project: Create a C code file in the project: at this time, you will be prompted whether to generate the Bridging Header and choose create.

 

The code structure after the file is created is as follows, you can see that there is a file named: <Project Name>-Bridging-Header.h, which is the file bridging between Swift and C.

 

In the configuration of the project, we can see that the bridge file is specified here, so if you forget to create this file, you don't have to worry about it. Just create a new file and specify it here.

 

Code for implementing C: MyCFile. h

 

MyCFile. c

 

Introducing the C code header file in the bridge file is very simple. Just import it directly.

 

Then, you can directly call the C method in the swift file:

 

Next we will add some code to implement two points: 1. Call Swift code in C code 2. Data Transmission (taking string as an example) MyCFile. h

C's call to the Swift method is actually equivalent to registering a global function pointer. For more information, see the definition of SwiftCallbackFun.

There are some OC Syntax: ^ operator, which indicates that this is a closure, that is, Block. Functions in Swift are transmitted in the form of closures. _ Nonnull indicates that the object should not be null, because during mixed compilation, the Swift compiler does not know whether an Objective-C object is optional or non-optional, therefore, Xcode 6.3 introduces a new Objective-C feature: nullability annotations, which can be defined as _ nullable or _ nonnull. MyCFile. c here is a callback to the Swift method.

 

Main. swift

 

The code in Swift should pay attention to two points: 1. The method for passing in string processing in C in Swift 2. assign a value to the global Callback first, in this way, the method from C to Swift can be called.