Lock screen by API in macOS

Question

Is there an API, that can lock the screen as the menu bar entry you can add from Keychain preferences?

This Keychain function is (was) lock

Answer 1

The following code does exactly what the Keychain menu item does since it just calls that. I used to use this (on 10.11 and 10.12), but this now fails on 10.13 (public beta) because there is no Keychain.menu nor menu item at all anymore. Mecki's answer is a working substitute but doesn't fade out the screen so it's really lower level.

void lock() {
    NSBundle *bundle = [NSBundle bundleWithPath:@"/Applications/Utilities/Keychain Access.app/Contents/Resources/Keychain.menu"];
    Class principalClass = [bundle principalClass];
    id instance = [[principalClass alloc] init];
    [instance performSelector:@selector(_lockScreenMenuHit:) withObject:nil];
}

Answer 2

I don't see anything documented as such, but the menu uses the ScreenSaver framework, which defines this:

@interface ScreenSaverDefaults : NSUserDefaults 
{
@private
    NSMutableDictionary     *_defaults;
    NSMutableDictionary     *_registeredDefaults;
    NSString                *_userName;
    NSString                *_domainName;
    BOOL                    _dirty;
    BOOL                    _screenLockPrefChanged;
}

+ (id) defaultsForModuleWithName:(NSString *)inModuleName;

@end