KeyDown and Cocoa Example

Question

I am learning how to create programs using Cocoa. I am using a sample Apple application that records video from a webcam. I would like to start and stop the video by capturing a keystroke. I tried to override the keydown event, but I read that this is not possible in NSObject. How can I handle such events?

The application class extends the class NSObject.

This is the code:

- (void)keyDown:(NSEvent *)event {
  NSLog(@"Hi there");
  NSString *characters = [event characters];
  if ([characters length]) {
    switch ([characters characterAtIndex:0]) {
      case NSUpArrowFunctionKey:
      NSLog(@"Key UP");
      break;
    }
  }
}

Answer 1

I tried to override the Keydown event, but I read that this is not possible in NSObject.

Correctly. The responder can only respond to events.

How can I handle this type of event?

. NSWindow NSWindowController . , .

Cocoa .

NSObject.

? , NSApplication - NSApplication.

PS: , MacOS?

Hillegass ( Apple), , , .

Answer 2

Cocoa - :

-, . - , ( ).

keyDown. , ( Safari Firefox, , ).

( Safari , ), , Guide. (, .)

, keyDown: , , . - keyDown:

, sendEvent:. sendEvent: , , , , .

Answer 3

NSWindow NSWindowController .

Similarly, you can subclass NSView and override its event handling methods.

What is a very good book to start learning MacOS programming?

Learning Objective-C on Mac from Dalrymple is very easy, covers enough bases, and moves fast enough to get you a little off the ground. It affects everything from Xcode and Interface Builder to OOP and Objective-C. Particularly useful for newbies (IMHO) are the source file organization and Foundation set-up chapters.

Good luck