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?

score 7 · Answer 1 · answered Mar 20 '13 at 21:34

7

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.

answered Mar 20 '13 at 21:34

codefrau

4,583
17
17

1

This works well and i didn't know it existed. But it uses the #step method of the Morph to ask for changes each step. Do you also know what a more "observer-pattern-like" solution could look like? – MartinW Mar 21 '13 at 10:16
1

You can use any of the frameworks, but nothing beats the simplicity of the Morphic stepping mechanism. This is how Morphic is intended to be used. – codefrau Mar 21 '13 at 13:01
Seems, i can only accept one answer. Feel both accepted and i voted both answers up :) – MartinW Mar 27 '13 at 18:05

MartinW · Answer 2 · 2015-07-27T09:22:44.327

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.

score 1 · Accepted Answer · answered Mar 21 '13 at 10:34

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.

Thank you, i start studying documentation and examples. This is very interesting. — MartinW, Mar 21 '13 at 19:45

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

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