Code to detect when hardware keyboard is attached / detached

SCKeyboardHardwareChanged.c

#include <objc/runtime.h>

// this is called when a keyboard is attached / detached, and
// isHardwareAttached will return YES / NO appropriately
void hardwareChangeIMP(id aSelf, SEL sel, BOOL isHardwareAttached) {
    SEL newSel = NSSelectorFromString(@"_modeChange:");
    [aSelf performSelector:newSel withObject:[NSNumber numberWithBool:isHardwareAttached]];
}

// call this to start capturing hardware changes
void captureKeyboardHardwareChanges() {
    Class kb = NSClassFromString(@"UIKeyboardImpl");
    SEL origSel = NSSelectorFromString(@"setInHardwareKeyboardMode:");
    SEL newSel = NSSelectorFromString(@"_modeChange:");
    class_addMethod(kb, newSel, (IMP)hardwareChangeIMP, @encode(BOOL));
    Method orig = class_getInstanceMethod(kb, origSel);
    Method alt = class_getInstanceMethod(kb, newSel);
    method_exchangeImplementations(orig, alt);
}