Fields of Struct are not changing with functions

Hello, I am trying to create a uifigure that will contain two uisliders, one that will change the frame of the image dataset that is depicted on the figure, and a uislider that will control the max range.

The problem i am facing is that , even i am calling the app struct inside the functions and I am changing the fields of frame and max range, the actual app.frames still equals to 1, even though when using the uislider for the frames, I am changing the frames. The same applies to MaxSlider; in the figure the contrast is chaning but when checking the app.displayRange field, I get the initial value I gave.

function draft_app
load("appImage.mat")
app.Figure=uifigure('Name',"A Process Try towards Improvemnet");
app.ax=uiaxes(app.Figure,'Position',[5 50 550 400]);
% ------------- Initialize Values ---------------
app.images=images;
n=size(app.images,3)
app.frame=1;
app.cmin=min(app.images(:,:,n),[],'all');
app.cmax=max(app.images(:,:,n),[],'all');
app.displayRange=[app.cmin app.cmax];
colorbar(app.ax);
app.im=imshow(app.images(:,:,app.frame),app.displayRange,'Parent',app.ax);
colormap(app.ax, jet);
% ---------------- Check Update -------------
update2(app);

%%

n=size(app.images,3);
app.frameSlider=uislider(app.Figure,'Limits',[1 n],"Position",[50 120 300 3],'Value',1);
app.frameSlider.MajorTicks = 1:1:n; % Define major ticks at intervals of 1
app.frameSlider.MinorTicks = 1:1:n; % Define minor ticks at smaller intervals, if needed
app.frameSlider.ValueChangingFcn = @(src, event) updateAppFrames(app,event.Value);
%updateAppImage(object,number,min,max)


%
app.MaxSlider=uislider(app.Figure,'Limits',[1 app.cmax],"Position",[50 100 300 3],'Value',app.cmax);
app.MaxSlider.MajorTicks = []; % Define major ticks at intervals of 1
app.MaxSlider.MinorTicks = []; % Define minor ticks at smaller intervals, if needed
app.MaxSlider.ValueChangingFcn = @(src, event) updateAppMax(app,event.Value);
end

function updateAppMax(app,maximum)
    app.cmax=maximum;
    app.displayRange=[app.cmin app.cmax];
    update2(app);
end

function update2(app)
    set(app.ax,'CLim',app.displayRange);
    fprintf('The range is %1.2f - %1.2f\n',app.displayRange(1),app.displayRange(2));
    set(app.im,'CData',app.images(:,:,app.frame));
end

function updateAppFrames(app,frame)
app.frame=round(frame);
% app.cmin=min(app.images(:,:,app.frame),[],'all');
% app.cmax=max(app.images(:,:,app.frame),[],'all');
% app.displayRange=[app.cmin app.cmax];
update2(app);
    

 end 

Answer 1

[Stephen23]

" even i am calling the app struct inside the functions and I am changing the fields of frame and max range, the actual app.frames still equals to 1"

If you simply pass a structure to a local function then any changes to the structure within that local function will remain within that local function. The changes are discarded when the function returns.

The MATLAB documentation explains how to pass data between callback functions:

https://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

https://www.mathworks.com/help/matlab/creating_plots/create-callbacks-for-graphics-objects.html

A simple and intuitive way to pass the data is to use nested functions. I modified your function to use nested functions, it works without error. I had to comment-out one command because you referred to a property that does not exist.

function draft_app
S = load("appImage.mat"); % much better to LOAD into an output variable.
S.Figure = uifigure('Name',"A Process Try towards Improvement");
S.ax = uiaxes(S.Figure,'Position',[5 50 550 400]);
%
%% Initialize Values
%
n = size(S.images,3);
S.frame = 1;
S.cmin = min(S.images(:,:,n),[],'all');
S.cmax = max(S.images(:,:,n),[],'all');
S.displayRange = [S.cmin,S.cmax];
colorbar(S.ax);
S.im = imshow(S.images(:,:,S.frame),S.displayRange,'Parent',S.ax);
colormap(S.ax, parula);
%
%% Check Update
%
update2();
%
n = size(S.images,3);
S.frameSlider = uislider(S.Figure,'Limits',[1,n],"Position",[50,120,300,3],'Value',1);
S.frameSlider.MajorTicks = 1:1:n; % Define major ticks at intervals of 1
S.frameSlider.MinorTicks = 1:1:n; % Define minor ticks at smaller intervals, if needed
S.frameSlider.ValueChangingFcn = @updateAppFrames;
%updateAppImage(object,number,min,max)
%
S.MaxSlider = uislider(S.Figure,'Limits',[1,S.cmax],"Position",[50,100,300,3],'Value',S.cmax);
S.MaxSlider.MajorTicks = []; % Define major ticks at intervals of 1
S.MaxSlider.MinorTicks = []; % Define minor ticks at smaller intervals, if needed
S.MaxSlider.ValueChangingFcn = @updateAppMax;
%
%% Nested Functions
%
    function updateAppMax(~,event)
        %S.cmax = event.maximum; % !!!! MAXIMUM is not a property of this EVENT !!!!
        S.displayRange=[S.cmin,S.cmax];
        update2();
    end
%
    function update2()
        set(S.ax,'CLim',S.displayRange);
        fprintf('The range is %1.2f - %1.2f\n',S.displayRange(1),S.displayRange(2));
        set(S.im,'CData',S.images(:,:,S.frame));
    end
%
    function updateAppFrames(~,event)
        S.frame = round(event.Value);
        % S.cmin=min(S.images(:,:,S.frame),[],'all');
        % S.cmax=max(S.images(:,:,S.frame),[],'all');
        % S.displayRange=[S.cmin,S.cmax];
        update2();
    end
%
end

[Dimitris Anestis]

Hello Stephen,

Thank you very much for the help. The modified script was not updating the contrast so I added S.cmax=event.Value to updateAppFrames function.

function draft_app
S = load("appImage.mat"); % much better to LOAD into an output variable.
S.Figure = uifigure('Name',"A Process Try towards Improvement");
S.ax = uiaxes(S.Figure,'Position',[5 50 550 400]);
%
%% Initialize Values
%
n = size(S.images,3);
S.frame = 1;
S.cmin = min(S.images(:,:,n),[],'all');
S.cmax = max(S.images(:,:,n),[],'all');
S.displayRange = [S.cmin,S.cmax];
colorbar(S.ax);
S.im = imshow(S.images(:,:,S.frame),S.displayRange,'Parent',S.ax);
colormap(S.ax, parula);
%
%% Check Update
%
update2();
%
n = size(S.images,3);
S.frameSlider = uislider(S.Figure,'Limits',[1,n],"Position",[50,120,300,3],'Value',1);
S.frameSlider.MajorTicks = 1:1:n; % Define major ticks at intervals of 1
S.frameSlider.MinorTicks = 1:1:n; % Define minor ticks at smaller intervals, if needed
S.frameSlider.ValueChangingFcn = @updateAppFrames;
%updateAppImage(object,number,min,max)
%
S.MaxSlider = uislider(S.Figure,'Limits',[1,S.cmax],"Position",[50,100,300,3],'Value',S.cmax);
S.MaxSlider.MajorTicks = []; % Define major ticks at intervals of 1
S.MaxSlider.MinorTicks = []; % Define minor ticks at smaller intervals, if needed
S.MaxSlider.ValueChangingFcn = @updateAppMax;
%
%% Nested Functions
%
    function updateAppMax(~,event)
        S.cmax = round(event.Value);
        %S.cmax = event.maximum; % !!!! MAXIMUM is not a property of this EVENT !!!!
        S.displayRange=[S.cmin,S.cmax];
        update2();
    end
%
    function update2()
        set(S.ax,'CLim',S.displayRange);
        fprintf('The range is %1.2f - %1.2f\n',S.displayRange(1),S.displayRange(2));
        set(S.im,'CData',S.images(:,:,S.frame));
    end
%
    function updateAppFrames(~,event)
        S.frame = round(event.Value);
        % S.cmin=min(S.images(:,:,S.frame),[],'all');
        % S.cmax=max(S.images(:,:,S.frame),[],'all');
        % S.displayRange=[S.cmin,S.cmax];
        update2();
    end
%
end

[Stephen23]

@Dimitris Anestis: I hope the my answer helped you. Please remember to click the accept button!