结束语C库用Objective-C的 - 函数指针 [英] Wrapping a C Library with Objective-C - Function Pointers

问题描述

我写周围的Objective-C的C库的包装。该库可以让我发生特定事件时注册回调函数。

I'm writing a wrapper around a C library in Objective-C. The library allows me to register callback functions when certain events occur.

该register_callback_handler（）函数的函数指针作为参数之一。

The register_callback_handler() function takes a function pointer as one of the parameters.

我给你的大师编程的​​问题是：我怎样才能重新present一个Objective-C的方法调用/选择器作为函数指针

My question to you gurus of programming is this: How can I represent an Objective-C method call / selector as a function pointer?

• 应该NSInvocation的是有用的在这种情况下什么过高的水平？


• 我会过得更好只是写有里面写的方法调用C函数，然后将指针传递给该函数？

任何帮助将是巨大的，谢谢。

Any help would be great, thanks.

推荐答案

确实 register_callback_handler（）也采取了（无效*）上下文参数？多数回调的API做的。

Does register_callback_handler() also take a (void*) context argument? Most callback APIs do.

如果确实如此，那么你可以使用NSInvocation的很容易。或者你可以分配包含对象和选择的引用，然后凑齐了自己的呼叫一点结构。

If it does, then you could use NSInvocation quite easily. Or you could allocate a little struct that contains a reference to the object and selector and then cobble up your own call.

如果只需要一个函数指针，那么你就可能大清洗。你需要的东西的地方，唯一标识的背景下，即使是纯C编码。

If it only takes a function pointer, then you are potentially hosed. You need something somewhere that uniquely identifies the context, even for pure C coding.

由于您的回调处理程序的确实的有上下文指针，你都设置：

Given that your callback handler does have a context pointer, you are all set:

typedef struct {
    id target;
    SEL selector;
    // you could put more stuff here if you wanted
    id someContextualSensitiveThing;
} TrampolineData;

void trampoline(void *freedata) {
    TrampolineData *trampData = freedata;
    [trampData->target performSelector: trampData->selector withObject: trampData-> someContextualSensitiveThing];
}

...
TrampolineData *td = malloc(sizeof(TrampolineData));
... fill in the struct here ...
register_callback_handler(..., trampoline, td);

这是一般的想法，反正。如果您需要处理非对象类型参数和/或回调，就有点有点棘手，但不算多。最简单的办法就是让编译器生成正确的判罚网站（请记住，你可能需要使用objc_msgSend_stret（）为结构的返回类型），其类型转换为正确的类型的函数指针后直接调用objc_msgSend（）。

That is the general idea, anyway. If you need to deal with non-object typed arguments and/or callbacks, it gets a little bit trickier, but not that much. The easiest way is to call objc_msgSend() directly after typecasting it to a function pointer of the right type so the compiler generates the right call site (keeping in mind that you might need to use objc_msgSend_stret() for structure return types).

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