how to override/swizzle a method of a private class in runtime objective-c?

Question

To give a bit of context of why I\'m asking this: basically I would like to change the location of the myLocationButton of the google map on iOS. So I first fet

Answer 1

UPDATE

If you want to preserve original implementation you can get it and call it inside the blockImp. Then after that call [[aClass superclass] layoutSubviews] or call it with function pointer. Note that all this code need some error check and exception prevents.

//get method encoding
const char * encoding = method_getTypeEncoding(class_getInstanceMethod(NSClassFromString(@"GMSUISettingsView"), @selector(layoutSubviews)));

void(^oldImplementation)(id aClass, SEL aSelector) = imp_getBlock(method_getImplementation(class_getInstanceMethod(NSClassFromString(@"GMSUISettingsView"), @selector(layoutSubviews))));

id blockImp = ^void(id aClass, SEL aSelector)
{
    //old imlpementation
    oldImplementation(aClass, aSelector);

    //calling [super layoutSubviews]
    IMP aImp = [[aClass superclass] methodForSelector:@selector(layoutSubviews)];
    id (*func)(id, SEL) = (void *)aImp;
    func([aClass superclass], @selector(layoutSubviews));
};
IMP newImp = imp_implementationWithBlock(blockImp);
class_replaceMethod(NSClassFromString(@"GMSUISettingsView"), @selector(layoutSubviews), newImp, encoding);

ORIGINAL ANSWER

I'm sorry but I didn't fully understand do you want to completely override 'layoutsubviews' or to have original implementation and change just part of it. If it's the first you could use class_replaceMethod instead of swizzling. It will have performance hits though! Something like this should do the trick:

//get method encoding
const char * encoding = method_getTypeEncoding(class_getInstanceMethod(NSClassFromString(@"GMSUISettingsView"), @selector(layoutSubviews)));

id blockImp = ^void(id aClass, SEL aSelector)
{
    //what you want to happen in layout subviews
};
IMP newImp = imp_implementationWithBlock(blockImp);
class_replaceMethod(NSClassFromString(@"GMSUISettingsView"), @selector(layoutSubviews), newImp, encoding);

I've not tested this on device/simulator but something like this should work for you. I assume you know it's not a really bright idea to manipulate private classes ;)