How to bind a LabelMorph/TextMorph to a variable so that the Morph reflects changes of the variable?

Question

• I have an object with a variable containing a String.
• I have a window containing a LabelMorph/TextMorph (or some other Morph that displays Text?).

How do i bind the LabelMorph/TextMorph to the variable, so that the label updates when the String in the variable changes?

• classic Smalltalk-80 dependent/change/update mechanism?
• Pharo Announcement framework?
• something different??

How would i do this? Which Morph should i use?

Answer 1

Depends on what you want to achieve. You might want to take a look at a way to do it with Glamour in a current Moose image. In a workspace, do-it:

GLMBasicExamples new magritte openOn: GLMMagrittePersonExample sampleData 

That shows how to work with announcements on save. The earlier examples are a better way to start understanding how to work with Glamour (and because of the way the examplebrowser is build, the Magritte example doesn't update the list when it is nested):

GLMBasicExamples open

That has several other examples that update on change.

Answer 2

Simplest is to use an updating String morph:

UpdatingStringMorph on: self selector: #myLabel

This will send #myLabel (or any other message) to self (or any other object) and display it.

Answer 3

This is a solution provided by Benjamin Van Ryseghem on the Pharo Mailinglist:

For this kind of situation, my solution is to use a ValueHolder. Instead of storing your string directly in an instance variable, store it into the ValueHolder.

I tried this in a Workspace:

|string label|

string := 'Wait till i change..' asValueHolder.
label := LabelMorph contents: string contents.
string whenChangedDo: [:newValue | label contents: newValue ].
label openInWindow.
[ 5 seconds asDelay wait. string value: 'I changed :)' ] fork.