例如通过方法函数指针C库 [英] Pass instance method as function pointer to C Library

问题描述

我写一个使用C库Objective-C的应用程序。我目前面临的问题是，C库，其中有一些场均函数指针后用作回调的结构。我怎么能一个Objective-C的实例方法转换为一个函数指针，并把它传递给库？

I am writing an Objective-C application that uses a C Library. The issue which i am currently facing is that the C Library has a structure where some field are function pointers later used as callbacks. How can i convert an Objective-C instance method to a function pointer and pass it to the library?

推荐答案

您需要提供的Objective-C类实现文件中以C回调函数，这只会工作，如果回调能够使用的上下文的某种指针。

You will need to provide the C callback function within the Objective-C class implementation file, and this will only work if the callback is able to use a context pointer of some sort.

所以，想象的C回调签名是这样的：

So imagine the C callback signature is like this:

void myCallback(void *context, int someOtherInfo);

然后，Objective-C类实现文件中，你需要使用回调蹦床回到您的Objective-C类（使用的背景的指针作为类的实例来调用）：

Then within the Objective-C class implementation file you need to use that callback to trampoline back into your Objective-C class (using the context pointer as the instance of the class to invoke):

// Forward declaration of C callback function
static void theCallbackFunction(void *context, int someOtherInfo);

// Private Methods
@interface MyClass ()
- (void)_callbackWithInfo:(int)someOtherInfo;
@end

@implementation MyClass

- (void)methodToSetupCallback
{
    // Call function to set the callback function, passing it a "context"
    setCallbackFunction(theCallbackFunction, self);
    ...
}

- (void)_callbackWithInfo:(int)someOtherInfo
{
    NSLog(@"Some info: %d", someOtherInfo);
}

@end

static void theCallbackFunction(void *context, int someOtherInfo)
{
    MyClass *object = (MyClass *)context;
    [object _callbackWithInfo:someOtherInfo];
}

如果你的C回调函数不接受某种的背景的信息，则：

If your C callback function does not accept some sort of context info, then:

1. 这是坏了，这应该是固定/报告的错误。


2. 您将需要依靠存储的指针到自我的在全球，静态的，范围可以通过C回调函数使用。这将 MyClass的的实例的数量限制到一个！

1. It's broken and this should be fixed/reported as a bug.
2. You will need to rely on storing a pointer-to-self at global, static, scope to be used by the C callback function. This will limit the number of instances of MyClass to one!

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