Why am i getting "Undefined function 'eq' for input arguments of type 'cell'." error?

Hello, I am new to matlab app designer and I was tasked to program an app that computes for delivery prices. although I am not sure why I am getting this error when i try to run my program. In the pickUpValue, I used Items data to set my Items to a certain value which is the same with dropOffValue.

pickUpValue = app.PickUpDropDown.ItemsData;
dropOffValue = app.DropOffDropDown.ItemsData;
            
if pickUpValue == '1' && dropOffValue == '1'
                totalLocCost = 30; 
                app.TotalShippingCostTextArea.Value = totalLocCost;

            else  
                 totalLocCost = 60;
            end

Answer 1

[Benjamin Kraus]

Are you trying to check the currently selected value, or the list of available values? The ItemsData stores the list of available values, not the currently selected value (which is stored in the Value property). In addition, your ItemsData does not need to be a cell-array.

For example, this will create a drop-down menu with four options, which are numbered 1-4.

% Create a drop-down menu with four pets, and assign them numbers from 1-4.
d = uidropdown('Items',{'Dog','Cat','Fish','Hamster'},'ItemsData',1:4);

% You would normally select a value interactively, but I'll select it
% programmatically for this example.
d.Value = 2; % Select 'Cat'.

% Now operate on the selected value.
value = d.Value;
if (value == 2)
    disp('You selected Cat');
end

Alternatively, you can leave the ItemData empty and operate directly on the cell-array of character vectors. However, if that is the case, then you probably want to use either isequal or strcmp or equality with a scalar string:

% Create a drop-down menu with four pets.
d = uidropdown('Items',{'Dog','Cat','Fish','Hamster'});

% You would normally select a value interactively, but I'll select it
% programmatically for this example.
d.Value = 'Cat';

% Now operate on the selected value.
value = d.Value;

% Using strcmp
if strcmp(value, 'Cat')
    disp('You selected Cat');
end

% Using strcmpi for case-insensitive match
if strcmpi(value, 'cat')
    disp('You selected cat');
end

% Using isequal
if isequal(value, 'Cat')
    disp('Your selection equals ''Cat''');
end

% Using equality to a string scalar
if value == "Cat"
    disp("Your selection equals the string 'Cat'")
end

[Benjamin Kraus]

Specifically, I see two issues with the code you posted:

pickUpValue = app.PickUpDropDown.ItemsData;
dropOffValue = app.DropOffDropDown.ItemsData;
            
if pickUpValue == '1' && dropOffValue == '1'
    totalLocCost = 30; 
    app.TotalShippingCostTextArea.Value = totalLocCost;
else  
    totalLocCost = 60;
end

1. You are using ItemsData instead of Value. I suspect what you want in this case is Value.
2. You shouldn't use == (which is the same as the eq function) on character vectors or cell-arays of character vectors.

This is how I would modify your code:

pickUpValue = app.PickUpDropDown.Value;
dropOffValue = app.DropOffDropDown.Value;
            
if pickUpValue == "1" && dropOffValue == "1"
    totalLocCost = 30; 
    app.TotalShippingCostTextArea.Value = totalLocCost;
else  
    totalLocCost = 60;
end

But, a better approach would be to populate your ItemData with a numeric vector, then you can use == with the numbers (see my original answer).