private properties for UI component in app designer

Hello everyone,

I am wondering if it is possible to access the private properties of the UI component in the external function. In my example, I have an EV_lite component and inside of it I use a “DropDownValueChanged” callback which executes a function outside the component:

However, this function gives us an error, because it requires a private property “CategoryEVDropDown”:

I have dozens of such properties. Could you advise how to declare these private properties as public or access them directly outside of the component?

Or the only option is to put all the code inside of the component?

Thank you in advance!

Answer 1

[Sandeep Mishra]

Hello Aleksandr,

I understand that you are trying to create a private property of the UI component, but you cannot access that function outside the component.

In MATLAB App Designer, you can create public UI components in the following ways

1. In Design view, Drag and Drop the UI component will make public UI component by default
2. In Code view, You can create new Public Property by selecting Public Property from Property option.
3. In Code view, You can change the "Access" modifier of properties from private to public like below

properties (Access = public)
    CategoryEVDropDown 
end

You can refer to the below documentation to learn more about MATLAB App Designer properties.

https://in.mathworks.com/help/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html

[Aleksandr Petrusev]

The problem is that "Access" modifier of properties is not editable. All states/values of objects (such as dropdown menus) are created with private property by default, and I couldn't find a way to make it public (drag and drop from component library also creates a private property). I can create a new public property, but this will not iimpact my existing private properties.

[Sandeep Mishra]

Which Matlab version are you using?

I tried creating a blank app in MATLAB online version and after dragging a "Drop Down" component,

I found it has public Access modifier

[Aleksandr Petrusev]

Can you try the same with a blank component, not with an app? I have the problem specifically with the UI component.

[Sandeep Mishra]

For MATLAB App Designer component,

You can create a new public property for UI components as below

properties (Access = public)
        DropDownPublicProperty
end

Initialise the public property as below by creating a PostSetupFcn callback (Refer the documentation https://in.mathworks.com/help/matlab/creating_guis/custom-ui-component-startup-tasks-in-app-designer.html )

function postSetupFcn(comp)
        comp.DropDownPublicProperty = comp.DropDown;
end

Now you can call you function and access the "DropDown" using "DropDownPublicProperty"

[Sandeep Mishra]

Also from you function, It seems like you need the "DropDown" value instead of whole component

So it is recommended to pass "DropDown" value from the component to the function, instead of whole Component.

[Aleksandr Petrusev]

Thank you. This approach works fine to get the value of the property. However, chaging DropDownPublicProperty doesn't impact initial DropDown. In the end, I found "dependent property" which allows both getting value of private property and change it:

https://www.mathworks.com/help/matlab/matlab_oop/access-methods-for-dependent-properties.html

I hope it will help others