How to get keyboard state in Objective-C without referring to NSEvent

Is it possible to get the keyboard state in Objective-C without referring to NSEvent?

In general I can't use NSResponder methods like -[NSResponder flagsChange开发者_StackOverflow中文版d:] but I need to know if the Command key is currently pressed.

I'm still wondering why you can't use NSEvent, but I'm going to answer the question anyways. Perhaps you're building a "command-line tool" and are only linked against Foundation? You're going to have to include at least one more framework. If you want to link against AppKit, you can (as I mentioned in the comments) use +[NSEvent modifierFlags]; this is a class method on NSEvent, so you can use it anywhere, without needing to have access to an individual event, to get the current state of the modifier keys as a bitmask. The docs explain the meaning of the bitmask.

if( NSCommandKeyMask & [NSEvent modifierFlags] ){
    NSLog(@"Oh, yeah!");
}

You can also get this info using Quartz Event Services. In this case you have to include the ApplicationServices framework*. The CGEventSource functions will give you the same bitmask you get from NSEvent:

CGEventFlags theFlags;
theFlags = CGEventSourceFlagsState(kCGEventSourceStateHIDSystemState);
if( kCGEventFlagMaskCommand & theFlags ){
    NSLog(@"Uh huh!");
}

*This is already included if you are, in fact, writing a Cocoa app -- it's part of Quartz.

Use this code when targeting macOS 10.12 or newer:

if (NSEventModifierFlagCommand & NSEvent.modifierFlags) {
    // Do whatever is needed
}