如何将 CFunctionPointer 转换为 EventHandlerUPP？

Question

我有一个名为 Foo_C_Func 的 C 函数，我需要将其用作回调。该应用程序的其余部分在 Swift 中编码。据我了解，以下代码应该可以工作，但我却收到编译器错误。

// typealias makes our function signature easier to read 

typealias Sig = ( EventHandlerCallRef, EventRef, UnsafeMutablePointer<Void>) -> OSStatus

// We need to make a CFunctionPointer to the C function 

var ptr = UnsafeMutablePointer<Sig>.alloc(1)
ptr.initialize( Foo_C_Func )
let c_ptr = COpaquePointer( ptr )

let proc_ptr = CFunctionPointer<Sig>( c_ptr ) as EventHandlerProcPtr

// now we should be able to create the EventHandlerUPP

let handler_upp = NewEventHandlerUPP( proc_ptr )

尝试构建失败并出现以下错误：

Undefined symbols for architecture x86_64:

"_Foo_C_Func", referenced from:

__TTOFSC10Foo_C_FuncFTVSs14COpaquePointerS_GVSs20UnsafeMutablePointerT___VSs5Int32 in Demo.o

"_NewEventHandlerUPP", referenced from:

__TFC17DemocfMS0_FT_S0_ in Demo.o

ld: symbol(s) not found for architecture x86_64

我还注意到，当我将鼠标悬停在最后一行时，Xcode 工具提示显示 NewEventHandlerUpp 的 return 类型为 (EventHandlerProcPtr) 而不是 EventHandlerProcPtr.

我做错了吗，还是无法在 Swift 内创建 EventHandlerUPP？

Answer 1

我为用户 MAH 发布了这个，尽管我已经放弃了原来的项目。以下代码在 Swift 3 中编译。我还没有检查它是否可以超出此范围。

import Carbon

func hotkey_callback( _:EventHandlerCallRef?, _ event:EventRef?, _ context:UnsafeMutablePointer<Void>? ) -> OSStatus {
    // Do stuff
    return noErr
}

let handler_ref_ptr = UnsafeMutablePointer<EventHandlerRef?>( allocatingCapacity: 1 )

let spec_ptr = UnsafeMutablePointer<EventTypeSpec>( allocatingCapacity: 1 )

spec_ptr.pointee = EventTypeSpec( eventClass: OSType( kEventClassKeyboard ), eventKind:  UInt32( kEventHotKeyPressed ) )

let hotkey_callback_pointer = hotkey_callback as! EventHandlerUPP

let status = InstallEventHandler( GetEventDispatcherTarget(), hotkey_callback_pointer, 1, spec_ptr, nil, handler_ref_ptr )

Answer 2

如果您使用的是 Swift 3，这里有一个替代答案。Swift 2 与 Swift 3 不同，前者很糟糕，而后者可用。

let hotkey_callback: EventHandlerUPP = { _, _, _ in
    // Do stuff
    return noErr
}

var handler: EventHandlerRef? = nil

var spec = EventTypeSpec( 
    eventClass: OSType(kEventClassKeyboard), eventKind:  UInt32(kEventHotKeyPressed) 
)

let status = InstallEventHandler( 
    GetEventDispatcherTarget(), hotkey_callback, 1, &spec, nil, &handler 
)

请注意，我们现在可以使用“&”来避免手动分配指针，并注意遵守非正式的 "EventHandlerUPP" 协议现在是明确的，不需要我们手动声明每个参数的类型。阅读起来容易多了:)

如何将 CFunctionPointer 转换为 EventHandlerUPP？

How to convert a CFunctionPointer to an EventHandlerUPP?

swift

callback

event-handling