在Objective-C类中混合C函数

I am writing an Objective-C class but it uses an API written in C. This is mostly fine as mixing C calls with Objective-C calls causes few problems.

我正在编写一个Objective-C类，但它使用了用C编写的API。这很好，因为使用Objective-C调用混合C调用几乎没有问题。

However one of the API call requires a call back method (example):

但是，其中一个API调用需要回调方法（示例）：

success = CFHostSetClient(host, MyCFHostClientCallBack, &context);

Where MyCFHostClientCallBack is a C function defined like this:

MyCFHostClientCallBack是一个C函数定义如下：

static void MyCFHostClientCallBack(CFHostRef host, CFHostInfoType typeInfo, const CFStreamError *error, void *info);

Can/How do I call an Objective-C method in place of this?
可以/如何使用Objective-C方法代替此方法？
Can/Should I mix C functions with my Objective-C calls?
可以/我应该将C函数与Objective-C调用混合使用吗？
How do I mix C functions with Objective-C methods?
如何将C函数与Objective-C方法混合使用？

4 个解决方案

#1

Mixing C and Objective-C methods and function is possible, here is a simple example that uses the SQLite API within an iPhone App: (course site)

可以混合使用C和Objective-C方法和函数，这是一个在iPhone App中使用SQLite API的简单示例:(课程网站）

Download the Zip file (09_MySQLiteTableView.zip)

下载Zip文件（09_MySQLiteTableView.zip）

C functions need to be declared outside of the @implementation in an Objective-C (.m) file.

需要在Objective-C（.m）文件中的@implementation之外声明C函数。

int MyCFunction(int num, void *data)
{
     //code here...
}

@implementation

- (void)MyObjectiveCMethod:(int)number withData:(NSData *)data
{
      //code here
}

@end

Because the C function is outside of the @implementation it cannot call methods like

因为C函数在@implementation之外，所以它不能调用像

[self doSomething]

and has no access to ivars.

并且无法访问ivars。

This can be worked around as long as the call-back function takes a userInfo or context type parameter, normally of type void*. This can be used to send any Objective-C object to the C function.

只要回调函数采用userInfo或context类型参数（通常为void *类型），就可以解决此问题。这可用于将任何Objective-C对象发送到C函数。

As in the sample code, this can be manipulated with normal Objective-C operations.

与示例代码中一样，可以使用正常的Objective-C操作来操作它。

In addition please read this answer: Mixing C functions in an Objective-C class

另外请阅读以下答案：在Objective-C类中混合C函数

#2

To call Objective-C code from a C callback I would use something like:

要从C回调调用Objective-C代码，我会使用类似的东西：

void * refToSelf;
int cCallback()
{
    [refToSelf someMethod:someArg];
}

@implementation SomeClass
- (id) init
{
     self = [super init];
     refToSelf = self;
}
- (void) someMethod:(int) someArg
{
}

#3

Can/How do I call an Objective-C method in place of this?

可以/如何使用Objective-C方法代替此方法？

You cannot.

你不能。

Can/Should I mix C function in with my Objective-C call?

可以/我应该将C函数与Objective-C调用混合使用吗？

Yes. Write a C function and use that as the callback to the CF function.

是。编写C函数并将其用作CF函数的回调函数。

How do I mix C function with Objective-C methods?

如何将C函数与Objective-C方法混合使用？

You can set self as the info pointer in your context structure. That will be passed to the callback. Then, in the callback, cast the info pointer back to id:

您可以将self设置为上下文结构中的信息指针。那将被传递给回调。然后，在回调中，将信息指针强制转换为id：

MyClass *self = (id)info;

You can then send self messages. You still can't directly access instance variables, though, since a C function is outside of the @implementation section. You'll have to make them properties. You can do this with a class extension. (Contrary to what that document says, you would not declare the extension inside @implementation, but in the same file with it, generally right above it.)

然后，您可以发送自我消息。但是，您仍然无法直接访问实例变量，因为C函数位于@implementation部分之外。你必须把它们作为属性。您可以使用类扩展来执行此操作。（与该文档所说的相反，你不会在@implementation中声明扩展名，而是在与它相同的文件中，通常在它上面。）

#4

What I've always found helpful in this situation is to make an Obj-C wrapper on top of the C API. Implement what you need to using C functions, and build an Objective-C class (or two) on top of it, so that's all the outside world will see. For example, in the case of a callback like this, you might make a C function that calls Obj-C delegate methods on other objects.

我总是发现在这种情况下有用的是在C API之上创建一个Obj-C包装器。实现使用C函数所需的内容，并在其上构建一个Objective-C类（或两个），以便外部世界都能看到。例如，在这样的回调的情况下，您可以创建一个C函数，在其他对象上调用Obj-C委托方法。

#1