APP DESIGNER: Issue with using properties between callback functions.

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Anupreet Singh 2022-2-10

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https://ww2.mathworks.cn/matlabcentral/answers/1646700-app-designer-issue-with-using-properties-between-callback-functions

评论： Anupreet Singh 2022-2-10

Hi,

I am working on an image segmentation GUI. When I load in my volume, I am storing it in a property I made called "app.volume". I do this as I want to use the volume between callback functions. I load in my volume in one callback function and assign app.volume the data. However, when I move onto the following callback function, in which I need to use the app.volume data, I am not able to retrieve it.

I am not sure why this is happening, and I need to be able to work with the volume between various callback functions. Any advice?

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Anupreet Singh 2022-2-10

在 MATLAB Online 中打开

% Button pushed function: SelectDICOMDirectoryButton
function SelectDICOMDirectoryButtonPushed(app, event)
    % User will select the DICOM directory of choice
    
    clc; clearvars; close all; % to clear anything that may have previously been loaded
    
    % to open windows directory, to find the image to be segmented
    desktop=winqueryreg('HKEY_CURRENT_USER', 'Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders', 'Desktop'); 
    desktop=strcat(desktop,'C:\Users\anupr\MATLAB Drive\capstone\saggitalSpinalCT');
    [PathName] = uigetdir(desktop);
    
    f = waitbar(0,'Loading DICOM Directory');
    pause(0.5)
    
    waitbar(.15,f,'Loading DICOM Directory');
    pause(3)
    
    % How many images are in the directory?
    a=dir([PathName '/*.dcm']);
    out=size(a,1);
    
    waitbar(.33,f,'Loading DICOM Directory');
    pause(2)
    
    waitbar(.50,f,'Loading DICOM Directory');
    pause(3)
    
    % read in the images
    name = extractfield(a,'name')';
    
    waitbar(.67,f,'Loading DICOM Directory');
    pause(2)
    
    for i=1:out
        holder = char(name(i));
        myFile = strcat(PathName,'\',holder);
        img(:,:,i)=dicomread(myFile);
        metadata(i) = dicominfo(myFile);
    end
    
    waitbar(.85,f,'Loading DICOM Directory');
    pause(2)
    
    waitbar(1,f,'Loading DICOM Directory');
    pause(0.1)
    close(f)
    clear f;
    
    
    app.volume = img;
    disp(size(app.volume))      
    app.metadata_vol = metadata;                    
end
% Button pushed function: ViewDICOMSeriesButton
function ViewDICOMSeriesButtonPushed(app, event)
    disp(size(app.volume))
    sliceViewer(app.volume);
end

Adam Danz 2022-2-10

Ah, I missed that. That clears your app object from the function workspace so when you assign data to app.volume, "app" becomes a structure variable which is cleared when the SelectDICOMDirectoryButtonPushed function ends. The "app" object still exists outside of the function but its values are gone which is why it retains the [0,0] size in the next callback function.

Lesson learned: there is rarely a need to clear variables within function workspaces. One exception is if a variable size is large and you no longer need it and want to reduce memory.

Anupreet Singh 2022-2-10

Hi Adam,

Yes that makes a lot of sense. Thank you so much for your help.

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采纳的回答

Cris LaPierre 2022-2-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1646700-app-designer-issue-with-using-properties-between-callback-functions#answer_893225

编辑：Cris LaPierre 2022-2-10

I think I have discovered the issue. In the SelectDICOMDirectoryButtonPushed() callback function, I have the following line at the beginning of the function:

clc; clearvars; close all; % to clear anything that may have previously been loaded

Ah, that's it.

That code clears the input variable app from the function workspace, so when you assign img to app.volume, you do so to a local variable, not the app property. Once the callback function finishes executing, that local variable is deleted. When you then call ViewDICOMSeriesButtonPushed, it passes in app without the volume property being populated.

You are in a function, so it is completely unnecessary to use any of that code. Your function starts with a brand new workspace with just the input variables. You do not need to clear, close, or clc anything.