MATLAB: GUI created by GUIDE returns different data types for uicontrol String property.

While building a GUI created by GUIDE, if I add a user interface control (uicontrol) such as an edit text component to the GUI using GUIDE, and later use the get command to retrieve the value of its String property in the GUI MATLAB file, Why does it return a cell array sometimes and a character array other times?

Best Answer

The return type depends on the way the 'String' property was set on the uicontrol created by GUIDE.

If you create a uicontrol in GUIDE and have not changed its String property, the 'get' command returns the 'String' value as a cell array.

If you change the 'String' property using the Property Inspector, the type of the returned data could be either cell array or character array depending on whether you edited the displayed string directly or you clicked the button to use the standalone string editor dialog box.

In order to enforce a certain type, you can add a statement similar to one of the following to the 'uicontrol' CreateFcn callback:

% Enforce character array type
>> set(hObject,'String','desired text');
% Enforce cell array type
>> set(hObject,'String',{'desired text'});

If later you change the value of the String property using the "set" command in your GUI M-file, 'get' returns the value as the type given by the 'set' command. If you change it interactively, e.g., by editing the contents of an edit text component, the data type is unchanged and 'get' returns the value as the type it had before the change.

Related Solutions

MATLAB: Do I get NaNs when I try to enter characters in the UITABLE object

This is the expected behavior when there is a "mis-match" between the Data property's type and the ColumnFormat property. In the example above, Data is a numeric type (cell(3,1) creates three empty numeric matrices) but ColumnFormat is being set to 'char'. A table in the following documentation page describes the expected behavior for all the possible combination of Data types and ColumnFormat settings:

http://www.mathworks.com/help/releases/R2009b/techdoc/ref/uitableproperties.html

To avoid this mis-match, in this case you should initialize the Data property of the uitable with a cell array of empty strings as follows:

data(1:3,1) = {''};
u=uitable('Data',data,'ColumnEditable',[true],'ColumnFormat',{'char'});

MATLAB: Using a ‘listbox’ in MATLAB R2015b, why do I receive the warning ‘Multiple-selection ‘listbox’ control requires that ‘Value’ be an integer within String range’

The error may be generated because the 'Value' property of the listbox is greater than the length of the cell array that is being assigned to the 'String' property. In other words, if the listbox has a 'Value' of 10, the cell array assigned to the 'String' property must have at least 10 elements.

To further demonstrate why the error might be occurring and to help with fixing the issue, consider the following code, which should run without errors in MATLAB R2015b:

>> MyString={'1','2','3','4','5'};
>> b=uicontrol('Style','listbox','Min',0,'Max',2,'Value',2);  % Value is less than the elements in 'MyString'
>> set(b,'String',MyString)

However, the following code will generate the error:

>> MyString={'1','2','3','4','5'};
>> b=uicontrol('Style','listbox','Min',0,'Max',2,'Value',10);  % Value is greater than the elements in 'MyString'
>> set(b,'String',MyString)

The difference between the two blocks of code above is that the second block of code has a 'Value' that is greater than the number of elements in the string.

Best Answer

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MATLAB: Do I get NaNs when I try to enter characters in the UITABLE object

MATLAB: Using a ‘listbox’ in MATLAB R2015b, why do I receive the warning ‘Multiple-selection ‘listbox’ control requires that ‘Value’ be an integer within String range’

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