How to handle a button double click

Question

I know how to define and IBAction and link it to a control by (Click-Drag)ing.
But that does not make me chose what action (event for x-Microsoft) in the control am I linking to.
By other words, when I click-drag, I dont mention, anywhere that I want this action to be linked to the "Click" event of a button. So what if I want this action method to be called when a button is double clicked for example, or when the mouse moves over it.
Thanks

Answer 1

Hi Tony, and welcome to the Dev Forum!
The good news is Apple provides thorough documentation on tracking, interpreting and handling Cocoa mouse events. The bad news is the info is carved into pieces that are scattered all over the library. The challenge is to identify the docs that contain one or more pieces of the puzzle, and then to fit everything together.
As to double clicks, there's no NSControl equivalent to the double-click notification that many Windows controls send (e.g. BN_DOUBLECLICKED). Also, as you've seen, when connecting an event to an action method in IB, there's only one event to choose from (Cocoa Touch is different in this regard, btw. You'll have a choice of several events when connecting a UIControl object to an action method in IB, though "double-touch" isn't among them).
So how do Cocoa programmers detect a double click in, for example, an NSButton? The default action message for this class is generated by a NSLeftMouseUp event. I.e. when the left button is released while the control is tracking the cursor.
One crude but effective solution is to have the listener (the action method connected to the button) set an ivar and start a one-shot timer on the first message. If a second message is received before the timer method resets the ivar, we have a double click. Otherwise we have two single clicks.
A more general solution is based on two methods you might easily overlook. Firstly, [setContinuous:|http://developer.apple.com/mac/library/documentation/Cocoa/Refe rence/ApplicationKit/Classes/NSCellClass/Reference/NSCell.html#//appleref/doc/uid/20000074-BBCCCEAA] allows you to configure the associated NSActionCell object to send a stream of messages to the button's target instead of just one. The stream starts with the mouse down event that initiated tracking and ends with the mouse up that ends tracking (also see [trackMouse:inRect:ofView:untilMouseUp:|http://developer.apple.com/mac/library/ documentation/Cocoa/Reference/ApplicationKit/Classes/NSCellClass/Reference/NSCell.html#//appleref/doc/uid/20000074-BBCCJAFJ]).
The next piece of the puzzle is the [currentEvent|http://developer.apple.com/mac/library/documentation/Cocoa/Refere nce/ApplicationKit/Classes/NSApplicationClass/Reference/Reference.html#//appleref/occ/instm/NSApplication/currentEvent] method of NSApplication. This returns the NSEvent object the started the current event cycle, i.e., the event which caused NSButton to send the current action message.
Thus the listener has access to the stream of event objects which represents the mouse activity from the start of tracking to the end. Using the position and time stamp data from this stream, the listener can distinguish between clicks and drags (hovering is detected differently; I won't try to cover that topic in this post).
A couple reference links that might help with the rest of the puzzle:
[Handling Mouse Events|http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/Ev entOverview/HandlingMouseEvents/HandlingMouseEvents.html#//apple_ref/doc/uid/100 00060i-CH6-SW1]
[Control and Cell Programming Topics for Cocoa|http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/Con trolCell/ControlCell.html#//apple_ref/doc/uid/10000015i]
Hope that helps!
\- Ray