How to swizzle a method of a private class

问题

I have a private class (both declared & defined within .m) as an addition to an implementation of a different class, that happens to use that private class internally.

I'd like to swizzle one of the methods of that private class.

I defined a category and did the usual:

+(void)load 
{
    Method original, swizzled;

    original = class_getInstanceMethod(objc_getClass("SomePrivateClass"), @selector(somePrivateMethod:));
    swizzled = class_getInstanceMethod(self, @selector(swizzled_somePrivateMethod:));
    method_exchangeImplementations(original, swizzled); 
}

The issue is that my implementation obviously doesn't know anything about this private class and self refers to the class I am adding the category to, whichever class that might be. So I have no way of calling the original implementation and in general working with the private class.

What is the proper approach to tackle this?

回答1:

Managed to get this to work, it's pretty simple actually.

So the way I did it:

made a NSObject category: @interface NSObject(PrivateSwizzleCategory)

swizzled:

+(void)load
{
    Method original, swizzled;

    original = class_getInstanceMethod(objc_getClass("SomePrivateClass"), @selector(somePrivateMethod:));
    swizzled = class_getInstanceMethod(self, @selector(swizzled_somePrivateMethod:));   
    method_exchangeImplementations(original, swizzled);
}

To call the original implementation, I had to cast self to NSObject:
```
id ret = [(NSObject *)self swizzled_somePrivateMethod:someParam];
```
To access private properties of the private class, I used valueForKey on self:
```
id privateProperty = [self valueForKey:@"__privateProperty"];
```

Everything works!

来源：https://stackoverflow.com/questions/22361427/how-to-swizzle-a-method-of-a-private-class

标签

ios

runtime

swizzling