objective-c 按名称创建objective-c 类实例？
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Create objective-c class instance by name?
提问by Mark
Is it possible to create an instance of a class by name? Something like:
是否可以按名称创建类的实例？就像是：
NSString* className = @"Car";
id* p = [Magic createClassByName:className];
[p turnOnEngine];
I don't know if this is possible in objective-c but seems like it would be,
我不知道这在 Objective-c 中是否可行，但似乎是这样，
回答by Chris McCall
id object = [[NSClassFromString(@"NameofClass") alloc] init];
回答by Simon Woodside
NSClassFromString()runs the risk of mistyping the class name or otherwise using a class that doesn't exist. You won't find out until runtime if you make that error. Instead, if you use the built-in objective-c type of Classto create a variable, then the compiler will verify that the class exists.
NSClassFromString()冒着错误输入类名或以其他方式使用不存在的类的风险。如果你犯了那个错误，你直到运行时才会发现。相反，如果您使用内置的objective-c 类型Class来创建变量，那么编译器将验证该类是否存在。
For example, in your .h:
例如，在您的.h：
@property Class NameOfClass;
and then in your .m:
然后在你的.m：
id object = [[NameOfClass alloc] init];
If you mistyped the class name or if it doesn't exist, you'll get an error at compile time. Also I think this is cleaner code.
如果你输入错误的类名或者它不存在，你会在编译时得到一个错误。另外我认为这是更干净的代码。
回答by Mark
If you are working with Objective-C without the NeXTstep(OS X, iOS, GNUstepetc) system or you just think this method is cleaner, then you could utilize the Objective-C language runtime library's API. Under Objective-C 2.0:
如果您正在使用Objective-C的工作没有NeXTstep（OS X，iOS，GNUstep等）的系统，或者你只是觉得这个方法更清洁，那么你可以利用Objective-C语言运行时库的API。下Objective-C 2.0：
#import <objc/runtime.h>
//Declaration in the above named file
id objc_getClass(const char* name);
//Usage
id c = objc_getClass("Object");
[ [ c alloc ] free ];
Under the Objective-C (1.0 or unnamed version) you would utilize the following:
在 Objective-C（1.0 或未命名版本）下，您将使用以下内容：
#import <objc/objc-api.h>
//Declaration within the above named file
Class objc_get_class( const char* name);
//Usage
Class cls = objc_get_class( "Test" );
id obj = class_create_instance( cls );
[ obj free ];
I haven't tested the 1.0version, however I have used the 2.0function in code that is now in production. I personally believe utilizing the 2.0function is cleaner if available than the NS function as it consumes less space: the length of the name in bytes + 1 ( null terminator )for the 2.0 API versus the sum of two pointers (isa, cstring), a size_t length (cstring_length), and the length of the string in bytes + 1for the NeXTSTEPAPI.
我还没有测试过这个1.0版本，但是我已经2.0在现在生产的代码中使用了这个功能。我个人认为利用该2.0功能是清洁如果有比NS功能，因为它消耗更少的空间：the length of the name in bytes + 1 ( null terminator )对于2.0 API相比the sum of two pointers (isa, cstring)，一size_t length (cstring_length)，和length of the string in bytes + 1对NeXTSTEPAPI。
回答by Skela
@interface Magic : NSObject
+ (id)createInstanceOfClass:(Class)classe;
@end
@implementation Magic
+ (id)createInstanceOfClass:(Class)classe
{
return [[classe alloc] init];
}
@end
Then to use it:
然后使用它：
Car *car = [Magic createInstanceOfClass:[Car class]];
[car engineTurnOn];
