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Calling a function defined in a m-file from within appdesigner app, with the app object as function input

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Lucademicus on 20 Dec 2019
Commented: Rik on 20 Dec 2019
I'm using R2019b.
I have created a GUI app using appdesigner and have written the function testFun in a m-file (testFun should also be usable by a non GUI approach, hence the m-file).
Within the app, I have declared a public property called someData:
properties (Access = public)
someData = '';
From within the GUI app, testFun is called with app as a function argument:
testFun is defined as follows:
function testFun(inputData)
inputData.someData = 'hello world';
As you can see, there are no output arguments defined in testFun.
Yet when I run the app like this, the someData property gets the value 'hello world'.
How can this behavior be explained?


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Accepted Answer

Rik on 20 Dec 2019
Edited: Rik on 20 Dec 2019
Your GUI (like all AppDesigner GUIs) has a pass-by-reference behavior (so it behaves like a handle class). That means the line you show modifies the original object, instead of creating a new one when the function is called.
You could create a GUI that doesn't work this way by using the normal figure class, so what is generally meant by a 'programmatic GUI', or GUIs created with GUIDE. For an overview of your options for GUI design, see this. For more information about pass-by-reference vs pass-by-value, see Comparison of handle and value classes in the documentation.


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Guillaume on 20 Dec 2019
A mlapp is a zip file that contains mostly text text files, so you could unzip the app/rezip the app as a pre/post commit task but yes I agree that for version control it's not ideal. As I said, it's far from perfect. In term of coding pattern, it's much better than GUIDE.
What I'd really like is something akin to the Visual Studio designer in .Net where you get just two (text) files: your class code (initialiser and callbacks) and the designer code (which you can edit if you know what you're doing).
Lucademicus on 20 Dec 2019
Alternatively I could create a little shell script which unzips myGUI.mlapp to myGUI/ everytime the mlapp-file is modified. This fits more readily in my Git workflow. Then I can keep the myGUI/ folder and the mlapp-file both within versioning. Any thoughts on this?
Rik on 20 Dec 2019
I don't know what the designer code equivalent would be in Matlab, but you could make a programmatic GUI based on a class instead of functions. That way you would have a text file for Git to work with.
But I'm not sure if that actually solves the issue, since you leave the AppDesigner to do this.

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