CCRuntime Objective-C 封装 runtime APIs

CCRuntime

CCRuntime 转换 MAObjCRuntime 为 ARC 模式

CCRuntime 是基于Objective-C 运行时封装的APIs集. 如果令人困惑, 它提供友好的面向对象接口基于/usr/include/objc中的C函数.

CCRuntime在BSD许可证下发布的。对于官方许可证，请参阅许可证文件。

快速开始

The action begins in CCRuntime.h. Various methods are added to NSObject to allow querying and manipulation. Most of these are class methods, because they operate on classes. There are a couple of instance methods as well. All of these methods start with cc_ to avoid name conflicts. The CCMethod and CCIvar classes are used to represent a single method and a single instance variable, respectively. Their use should be fairly obvious.

查询

You can query any class’s methods, instance variables, or other attributes using the methods provided. For example:

// get all subclasses of a class
NSArray *subclasses = [MyClass cc_subclasses];

// check out the methods on NSString
NSArray *methods = [NSString cc_methods];
for(CCMethod *method in methods)
    NSLog(@"%@", method);

// does it have any ivars?
NSLog(@"%@", [NSString cc_ivars]);

// how big is a constant string instance?
NSLog(@"%ld", (long)[[@"foo" cc_class] cc_instanceSize]);

修改

You can add new methods using +cc_addMethod:. You can modify the implementation of an existing method using the -setImplementation: method on CCMethod. Example:

// swizzle out -[NSObject description] (don't do this)
static NSString *NewDescription(id self, SEL _cmd)
{
    return @"HELLO WORLD!";
}

CCMethod *description = [NSObject cc_methodForSelector: @selector(description)];
[description setImplementation: (IMP)NewDescription];

You can create new classes using +cc_createSubclassNamed: or +cc_createUnregisteredSubclassNamed:. Note that if you want to add instance variables to a class then you have to use the Unregistered version, and add them before registering the class.

Objects

Two instance methods are provided as well. -cc_class exists because Apple likes to fiddle with the return value of -class, and -cc_class always gives you the right value. -cc_setClass: does pretty much what it says: sets the class of the object. It won’t reallocate the object or anything, so the new class had better have a memory layout that’s compatible with the old one, or else hilarity will ensue.

发送消息

After getting a list of methods from a class, it’s common to want to actually use those on instances of the class. CCMethodprovides an easy method for doing this, as well as several convenience wrappers around it.

The basic method for sending messages is -[CCMethod returnValue:sendToTarget:]. You use it like this:

CCMethod *method = ...;
SomeType ret;
[method returnValue: &ret sendToTarget: obj, CCARG(@"hello"), CCARG(42), CCARG(xyz)];

It may seem odd to have the return value at the beginning of the argument list, but this comes closest to the order of the normal ret = [obj method] syntax.

All arguments must be wrapped in the CCARG macro. This macro takes care of packaging up each argument so that it can survive passage through the variable argument list and also includes some extra metadata about the argument types so that the code can do some basic sanity checking. No automatic type conversions are performed. If you pass a double to a method that expects an int, this method will abort. That checking is only based on size, however, so if you pass a float where an int is expected, you’ll just get a bad value.

Note that while it’s not 100% guaranteed, this code does a generally good job of detecting if you forgot to use the CCARGmacro and warning you loudly and calling abort instead of simply crashing in a mysterious manner. Also note that there is no sanity checking on the return value, so it’s your responsibility to ensure that you use the right type and have enough space to hold it.

For methods which return an object, the -[CCMethod sendToTarget:] method is provided which directly returns idinstead of making you use return-by-reference. This simplifies the calling of such methods:

CCMethod *method = ...;
id ret = [method sendToTarget: obj, CCARG(@"hello"), CCARG(42), CCARG(xyz)];

There is also an NSObject category which provides methods that allows you to switch the order around to be more natural. For example:

CCMethod *method = ...;
id ret = [obj cc_sendMethod: method, CCARG(@"hello"), CCARG(42), CCARG(xyz)];

And the same idea for cc_returnValue:sendMethod:.

Finally, there are a pair of convenience methods that take a selector, and combine the method lookup with the actual message sending:

id ret = [obj cc_sendSelector: @selector(...), CCARG(@"hello"), CCARG(42), CCARG(xyz)];
SomeType ret2;
[obj cc_returnValue: &ret2 sendSelector: @selector(...), CCARG(12345)];