App designer - issue with app freezing after performing the first task

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Teshan Rezel
Teshan Rezel on 24 Mar 2021
Edited: Adam Danz on 29 Mar 2021
Hi folks,
I have an app that's meant to display an image from a folder with plots on them in the shape of a crosshair.
Currently, it is freezing after loading the image folder and displaying the first image, and I'm uncertain as to why.
Could you please point me in the direction of where my code is incorrect?
checkMatrix is a matrix of 9 checkbox values.
The issue appears to be in the "DisplayCrosshairs" section. The very first line causes the programme to sieze up and become completely un-interactable.
Thanks
methods (Access = private)
function ROI(app, index1, index2)
hold on
plot(index1, index2, app.innerMarkerStyle, 'MarkerSize', app.CrosshairThickness.Value, 'Color', app.crossHairColour);
plot(index1, index2, app.outerMarkerStyle, 'MarkerSize', app.CrosshairThickness.Value, 'Color', app.crossHairColour);
end
function DisplayCrosshairs(app)
[rows, columns] = size(app.Image, [1, 2]);
quarterHeight = rows*0.25;
halfHeight = rows*0.5;
threeQuarterHeight = rows*0.75;
quarterWidth = columns*0.25;
halfWidth = columns*0.5;
threeQuarterWidth = columns*0.75;
checkMatrix = [app.TopLeft.Value app.TopMiddle.Value app.TopRight.Value app.CentreLeft.Value app.CentreMiddle.Value app.CentreRight.Value app.BottomLeft.Value app.BottomMiddle.Value app.BottomRight.Value];
app.numSamplesPerImage = sum(checkMatrix, 1:9);
if checkMatrix(1) == 1
ROI(app, quarterHeight, quarterWidth);
elseif checkMatrix(2) == 1
ROI(app, quarterHeight, halfWidth);
elseif checkMatrix(3) == 1
ROI(app, quarterHeight, threeQuarterWidth);
elseif checkMatrix(4) == 1
ROI(app, halfHeight, quarterWidth);
elseif checkMatrix(5) == 1
ROI(app, halfHeight, halfWidth);
elseif checkMatrix(6) == 1
ROI(app, halfHeight, threeQuarterWidth);
elseif checkMatrix(7) == 1
ROI(app, threeQuarterHeight, quarterWidth);
elseif checkMatrix(8) == 1
ROI(app, threeQuarterHeight, halfWidth);
elseif checkMatrix(9) == 1
ROI(app, threeQuarterHeight, threeQuarterWidth);
else
msgbox('Please select a quadrant for the crosshair to be displayed in');
end
end
function DisplayImage(app)
app.currentImage = fullfile(app.imageFolder(app.imageNumber).folder, app.imageFolder(app.imageNumber).name);
app.Image.Position = [0 0 app.UIFigure.Position(3:4)];
app.img = imread(app.currentImage);
app.uiImage = uiimage(app.UIFigure, 'imagesource', app.currentImage, "Position", app.Image.Position);
DisplayCrosshairs(app);
end
function LoadFolder(app)
app.imageFolder = dir(fullfile(app.filePath, '*.jpg'));
app.fileNumber = numel(app.imageFolder);
end
function CheckEndOfList(app)
if app.imageNumber < app.fileNumber
app.imageNumber = app.imageNumber +1;
else
msgbox('You have reached the last image');
end
end
end
function startupFcn(app)
pause(1);
app.UIFigure.WindowState = 'maximized';
app.Counts = [zeros(8, 1)];
app.Percentages = [zeros(8, 1)];
app.CokeTable.Data = [app.Counts, app.Percentages];
app.CokeTable.Position = [73 -1 168 265];
app.tallyOrder = [1];
app.innerMarkerStyle = '+';
app.outerMarkerStyle = 'o';
app.crossHairColour = 'w';
app.ImageNumber.Value = app.imageNumber;
app.TotalNumber.Value = app.fileNumber;
end
function AddImageFolderMenuSelected(app, event)
app.filePath = uigetdir(pwd);
addpath(app.filePath);
LoadFolder(app);
DisplayImage(app);
CheckEndOfList(app);
app.ImageNumber.Value = app.imageNumber;
app.TotalNumber.Value = app.fileNumber;
end
  5 Comments

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Accepted Answer

Adam Danz
Adam Danz on 26 Mar 2021
>At this point, a figure called "Figure 2" pops up
That's because you're not using axis handles to specify the parent in these lines below
function ROI(app, index1, index2)
hold on
plot(index1, index2, app.innerMarkerStyle, 'MarkerSize', app.CrosshairThickness.Value, 'Color', app.crossHairColour);
plot(index1, index2, app.outerMarkerStyle, 'MarkerSize', app.CrosshairThickness.Value, 'Color', app.crossHairColour);
end
Instead, replace app.UIAxes below with your axis handle.
function ROI(app, index1, index2)
hold(app.UIAxes,'on')
plot(app.UIAxes, index1, index2, app.innerMarkerStyle, 'MarkerSize', app.CrosshairThickness.Value, 'Color', app.crossHairColour);
plot(app.UIAxes, index1, index2, app.outerMarkerStyle, 'MarkerSize', app.CrosshairThickness.Value, 'Color', app.crossHairColour);
end
> and the main app freezes
No, it doesn't freeze. Execution stops because of an error!
  4 Comments
Adam Danz
Adam Danz on 29 Mar 2021
Are you referring to the ROI(app, index1, index2) function?
What have you tried to do to fix it?
You can get the size of the image using
size(I)
where I is your image data. You can get the center of the image using
size(I)/2
If there is space in the margins between the image and the axes use
axis(app.UIAxes, 'tight')

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More Answers (1)

Jan
Jan on 24 Mar 2021
Appending folders to Matlab's PATH can lead to unexpected side effects, if the folders contain Matlab files. So avoid addpath but use absolute path names using app.filePath and fullfile() - as you do already. So remove this line:
addpath(app.filePath);
But this is most likely not the source of the problem.
Adam's suggestion to use the debugger to step through the code line by line is the way to locate the line, which causes the troubles.
  6 Comments
Teshan Rezel
Teshan Rezel on 26 Mar 2021
Hi @Adam Danz and @Jan, I think it seems to fail when it gets to the "if" statement within the DisplayCrosshairs function. At this point, a figure called "Figure 2" pops up with a small crosshair at its centre, and the main app freezes. I'm not sure how to pass make "plot" draw the crosshair on the app.Image property though

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