Method swizzling a private framework iOS API

Question

I know there are countless resources on method swizzling. However is it possible to swizzle a method from a private API? The problem is that there are no header files. I would like to swizzle a method from a private class in a PrivateFramework such as (random example) Message.framework methods

This is for personal testing, I understand that it will get rejected to oblivion by Apple.

Answer 1

You can use NSClassFromString to get Class and use runtime library to perform method swizzling. No header files required. You just need to know class name and method signature.

sel_getUid can be used when @selector(somePrivateMethod) give your error about somePrivateMethod is not valid selector (because header is not available)

Code taken from my Xcode plugin

SEL sel = sel_getUid("codeDiagnosticsAtLocation:withCurrentFileContentDictionary:forIndex:");
Class IDEIndexClangQueryProviderClass = NSClassFromString(@"IDEIndexClangQueryProvider");

Method method = class_getInstanceMethod(IDEIndexClangQueryProviderClass, sel);
IMP originalImp = method_getImplementation(method);

IMP imp = imp_implementationWithBlock(^id(id me, id loc, id dict, IDEIndex *idx) {
    id ret = ((id (*)(id,SEL,id,id,id))originalImp)(me, sel, loc, dict, idx);

    // do work

    return ret;
});

method_setImplementation(method, imp);