Programmer Reference : Common Widgets : Drawing area widgets : Adding an event handler to a drawing area
Adding an event handler to a drawing area
In the following example, a button press event handler is used to detect double-clicks in a drawing area. The open method creates the widgets, and the buttonPress:clientData:event: method handles button press events.
Object subclass: #DoubleClick
instanceVariableNames: 'clickStartTime '
classVariableNames: ''
poolDictionaries: 'CgConstants CwConstants '
"Create a drawing area inside a shell."
| shell drawingArea |
clickStartTime := 0.
shell := CwTopLevelShell
createApplicationShell: 'shell'
argBlock: [:w | w title: 'Double-click test'].
(drawingArea := shell
createDrawingArea: 'draw'
argBlock: [:w |
width: 100;
height: 100])
addEventHandler: ButtonPressMask
receiver: self
selector: #buttonPress:clientData:event:
clientData: nil.
shell realizeWidget.
buttonPress: widget clientData: clientData event: event
"Detect double click by checking whether the time between successive
presses of the left mouse button is less than the system-defined
double-click time."
event button = 1
ifTrue: [
event time - clickStartTime < widget display doubleClickInterval
ifTrue: [
clickStartTime := 0.
Transcript cr; show: 'DOUBLE CLICK' ]
ifFalse: [
clickStartTime := event time ]].
Adding a mouse down event handler to a widget that processes mouse events internally, such as a CwPushButton, might result in unpredictable behaviour. To detect double-clicks in a CwList, use the defaultAction callback.
Last modified date: 01/29/2015