在 Objective-C 类中混合 C 函数 [英] Mixing C functions in an Objective-C class

问题描述

我正在编写一个 Objective-C 类，但它使用的是用 C 编写的 API.这基本上没问题，因为将 C 调用与 Objective-C 调用混合会导致很少的问题.

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.

但是其中一个 API 调用需要回调方法(示例):

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

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

其中 MyCFHostClientCallBack 是一个 C 函数，定义如下:

Where MyCFHostClientCallBack is a C function defined like this:

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

1. 能否/如何调用 Objective-C 方法来代替此方法?
2. 我可以/应该将 C 函数与我的 Objective-C 调用混合使用吗?
3. 如何将 C 函数与 Objective-C 方法混合使用?

推荐答案

混合 C 和 Objective-C 的方法和功能是可能的，这里是一个在 iPhone 应用程序中使用 SQLite API 的简单示例:(课程网站)

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)

下载 Zip 文件 (09_MySQLiteTableView.zip)压缩包)

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

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

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

@implementation

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

@end

因为 C 函数在 @implementation 之外，它不能调用像

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

[self doSomething]

并且无法访问 ivars.

and has no access to ivars.

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

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.

如示例代码，这可以用普通的 Objective-C 操作来操作.

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

另外请阅读这个答案:Mixing CObjective-C 类中的函数

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