Is there a KeyUp: method for flagsChanged:?

I have implemented the - (void)flagsChanged:(NSEvent *)theEvent method in my application. It works fine when I hold down the [alt] key. The method only sends when the key is pressed, but not when I let it go again. The - (void)keyUp:(NSEvent *)theEvent won't be called. Is there anyway to see when the [alt] key is released?

Here is the code:

- (void)flagsChanged:(NSEvent *)theEvent
{
    if([theEvent modifierFlags] & NSAlternateKeyMask)
    {
        NSLog(@"alt is down!!!");
    }
}

Okay. I really need to test the code a bit more. After logging the NSEvent, I noticed that the keyUp method is already implemented (thanks Jonathan Grynspan for pointing it out in the comment).

So now my code is:

- (void)flagsChanged:(NSEvent *)theEvent
{
    if([theEvent modifierFlags] & NSAlternateKeyMask)
    {
        NSLog(@"alt is down!!!");
    }
    else if([theEvent keyCode] == 58)
    {
        NSLog(@"alt is up!!!");
    }
}

This now works fine!