image callback in app designer

I have an app with a UIAxes which contains an image with the returned image object im i.e.im=image(UIAxesObject, array). I create a buttondownfcn callback using

im.ButtonDownFcn = @FCN. However, if I create the function FCN(app, event) inside the private or public function area of the app designer I get an error. The only way I seem to be able to get the callback to work is to put function FCN in a separate m. file. Is there another way of creating callback functions in app designer?

[Guillaume]

I get an error

What is the full text of the error message?

[Gordon Edwards]

The error message is when the callback function is a private method is ---

Undefined function 'ImageButtonDownCallBack' for input

arguments of type 'matlab.graphics.primitive.Image'.

Error while evaluating Image ButtonDownFcn.

Answer 1

[Guillaume]

You may want to consider using a uiimage instead of an Image inside a uiaxes.

I suspect you've defined the callback incorrectly. Typically the code would be something likle

classdef myapp < matlab.apps.AppBase
    % Properties that correspond to app components
    properties (Access = public)
        UIFigure  matlab.ui.Figure
        UIAxes    matlab.ui.control.UIAxes
        %... other controls. You can't edit this directly
    end
    
    %your own properties
    properties (Access = private)
        myimage;   %property to hold the image
    end
    
    %...
    methods (Access = private)
        function ImageButtonDownCallback(app, source, eventargs)
            %... the callback code
        end    
            
        %The function that creates the image and enable the callback
        function something(app)
           app.myimage = imshow(someimage, 'Parent', app.UIAxes);  %image creation
           app.myimage.ButtonDownFcn = @app.ImageButtonDownCallback;  %create callback. IMPORTANT: You must use app.****
        end
    end
end

[Gordon Edwards]

Thankyou - that works fine. I hadn't realised that the syntax @app.ImageButtonDownCallback is required.

I use the image function as I am creating one in UIAxes from an array. I find MatLab's nomenclature confusing at times - for example, use of the word 'image' as a function displaying an image from an array and also, in app designer, for an icon.

[Guillaume]

Indeed, you have:

• the image function
• the image type, returned by image, imshow, imagesc and probably other functions. The full name of that type is actually matlab.graphics.primitive.Image. It's not really well documented. The only doc page is its property page.
• the app designer image control whose full name is matlab.ui.control.Image. Again, not very well documented. It has a different set of properties and callbacks from the previous image type.