Mac Cocoa: How to differentiate if a NSScrollWheel

问题:

In my application, I want the scrolling to happen, only with scroll wheel action from a mouse and not from the two finger gesture on a trackpad. Basically, I am trying to determine if the scrollWheelEvent is generated from the mouse or trackpad, inside - (void)scrollWheel:(NSEvent *)theEvent method. From what I know so far, it seems like there is no straightforward way to accomplish this.

I tried a work around of setting a boolean variable to true and false inside -(void)beginGestureWithEvent:(NSEvent *)event; and -(void)endGestureWithEvent:(NSEvent *)event; But this is not a solution because the scrollWheel: method is getting called several times, after the endGestureWithEvent: method is called.

Here is my code:

    $BOOL fromTrackPad = NO;

    -(void)beginGestureWithEvent:(NSEvent *)event;
    {
        fromTrackPad = YES;    
    }

    -(void) endGestureWithEvent:(NSEvent *)event;
    {
        fromTrackPad = NO;    
    }

    - (void)scrollWheel:(NSEvent *)theEvent
    {
       if(!fromTrackPad)
       {
          //then do scrolling
       }
       else 
       {
         //then don't scroll
       }
    }

I know this is something that is not standard, but this is my requirement. Does anyone know a way to do this?? Thanks!

回答1:

-[NSEvent momentumPhase] is the solution. So, the events generated from the trackpad between the beginGesture and endGesture events returns a value other than NSEventPhaseNone for -[NSEvent phase] and the trackpad events that are generated after the endGesture event returns a value other than NSEventPhaseNone for -[NSEvent momentumPhase]. The code is below,

 - (void)scrollWheel:(NSEvent *)theEvent
    {
       if(([theEvent momentumPhase] != NSEventPhaseNone) || [theEvent phase] != NSEventPhaseNone))
       {
          //theEvent is from trackpad           
       }
       else 
       {
         //theEvent is from mouse
       }
    }

回答2:

You can use [event hasPreciseScrollingDeltas] to differentiate. It was added in OS X Lion. It differentiates between line scroll (mouse wheels) and pixel scroll (trackpads, magic mouse) events.

回答3:

My answer in Swift, but for Objective C logic is the same:

override func scrollWheel(with event: NSEvent) {
  if event.subtype == .mouseEvent {
    // mouse
  } else {
    // trackpad
  }
}

回答4:

The answer given by @AProgrammer maybe not available. Because scrollwheel event generated by magic mouse has phase values of: began, changed and ended. And scrollwheel event generated by mighty mouse has value of none for both phase and momentumphase. So the method can only distinguish mighty mouse from magic mouse and trackpad.