Because your drawOn: method doesn't draw anything and needs help from super.
It seems to me that you need to read more documentation :-)
On 05.02.2015 15:53, nacho wrote:
That work perfectly. What a silly mistake!!!
Of course it should have been position := aPoint.
Now, is it possible write the drawOn: method without calling super
drawOn: a Canvas?
I don't completely get it why I should call super drawOn: aCanvas
thanks
nacho
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On Thu, Feb 5, 2015 at 11:28 AM, Trygve Reenskaug [via Smalltalk]
<[hidden email] </user/SendEmail.jtp?type=node&node=4803979&i=0>> wrote:
I've tested your code in Squeak and found another bug (I should
have been more careful when I read your code. Shame on me.)
In class Ball you have the methods
position: aPoint
super position: aPoint.
This does not set a value to your position variable in class Ball, but
actually sets the upper-left corner of the bounds.
You should have said position := aPoint.
--------------------------------
The following now works in mySqueak image:
EllipseMorph subclass: #Ball
instanceVariableNames: 'position'
classVariableNames: ''
poolDictionaries: '' "this part is needed in Squeak"
category: 'ZZZtesting'
drawOn: aCanvas
self borderWidth:10; borderColor: Color green.
super drawOn: aCanvas.
position
^ position.
position: aPoint
position := aPoint.
I then execute the following in a workspace
| aBall |
aBall := Ball new.
aBall position: ( 10@10 ).
aBall openInWorld.
and it seems to work. But closer scrutiny shows that it ignores
your instance variable (position). when I move the ball around.
The reason is that EllipseMorph is a superclass of your Ball and
cannot possibly know about an instance variable (position) that is
defined in the subclass (Ball).
I ignored Ball>position since the EllipseMorph doesn't use it:
EllipseMorph subclass: #Ball
instanceVariableNames: ''
classVariableNames: ''
poolDictionaries: ''
category: 'ZZZtesting'
position
^ super position.
position: aPoint
super position: aPoint.
This looks better.
I you really want to replace the EllipseMorph>position you must go
deeper into how the EllipseMorph handles its position and bounds .
This will not be trivial. Much easier to invent a new instance
variable and use it in the drawOn: method.
Good luck with your apprenticeship
On 05.02.2015 11:56, nacho wrote:
@Trygve
I've checked and it doesn't work. I can't even bring the halo on to delete
the morph. The debugger keeps popping.
Thanks anyway to all
Nacho
-----
Nacho
Smalltalker apprentice.
Buenos Aires, Argentina.
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