在Objective-C中动态加载类？

Question

Is there a way to #import a class from a string in Objective-C at run time? Any methods that would produce a similar result would also be welcome.

Edit:

I want access to a class whose name I determine at runtime. So something like this:

NSString *className = getClassName();
Class myClass = loadClass(className);
myClass *myVar = [[myClass alloc] init];

Is there any way to do this without putting a static #import directive for myClass at the top of the file?

Answer 1

You can use NSClassFromString method. So:

// Creates an instance of an NSObject and stores it in anObject
id anObject = [[NSClassFromString(@"NSObject") alloc] init];

Some more sample code in response to your edit:

NSString* myClassString = getClassName();
// if the class doesn't exist, myClass will be Nil and myVar will be nil
Class* myClass = NSClassFromString(myClassString);
id myVar = [[myClass alloc] init];

Answer 2

The #import directive does not "import" a class — it inserts the text from the named file into the current file. This obviously isn't useful at runtime after the source has been compiled.

What you want is to create a bundle with the classes and dynamically load the bundle . In order to be able to talk to the classes from the core program, you'll probably want to have some common protocol that bundled classes implement.

Answer 3

感谢Chuck为我指明了正确的道路，但是此查询的正确答案似乎是在iOS 4.1上是不可能的，尽管当前的Mac OSX SDK使用可加载的包是可能的。