Waitbar message disappears and can't be updated (GUI)

I am working on a GUI which analyzes data using quite lengthy calculations. I am trying to implement waitbars to show the progression of serveral different processes that the GUI performs. However, in the case of one of those processes, my waitbar progresses, but the message just above it disappears when I first update the bar. If I try to include the message in subsequent waitbar calls (waitbar(x,h,'updated message')), Matlab returns an error ('Improper arguments for waitbar').

I won't include code here since the calls to this waitbar span several functions. In brief, I first call and create the waitbar in a callback function of my main interface m file (it activates after the user presses on a button which triggers a calculation). Afterwards, I update the waitbar in several 'for loops' contained in seperate functions that the callback function inside the main interface calls. I made the handle of the waitbar global so I could call it inside my different functions, and I specify the handle every time I update the waitbar. The message still does not display after the first call, though.

What could be causing this? Is it possible to use a waitbar to monitor the progress of a process that spans several functions?

[Stephen23]

A wild guess in the dark here, but perhaps there are some functions or scripts which contain the dreaded close all or close all hidden or the like. Although beginners love putting these into all of their files, such scatter-gun approach to programming is hardly robust, and leads to exactly this kind of hard-to-track-down bug.

[Walter Roberson]

Or "clear all" ! That one messes up your whole program.

[Rosalie Martel]

There is no 'close all' or 'clear all' in my program, except at the beginning. There is none in the span of code covered by the waitbar.

Answer 1

[Walter Roberson]

something is destroying the waitbar()

A waitbar is a figure. I suggest you attach a UserData to it that is an OnCleanup object that displays the call stack at the time of the destruction.

h = waitbar(....);
set(h, 'UserData', onCleanup(@() dbstack('-completenames')));

[Rosalie Martel]

Thank you for your input. The only instance that is identified by this command is the 'close(h)' command I used when I'm finished with the waitbar... As a side note, the waitbar() is not exactly destroyed; it is only the message above it that disappears and that I can't update.

[Stephen23]

How are you accessing this text? Do you keep track of its handle, or are you using some other method?

[Rosalie Martel]

It is the message you can add when first calling waitbar(), as follows: h = waitbar(x,'message')

I followed the example present in the Matlab help page for 'waitbar': http://www.mathworks.com/help/matlab/ref/waitbar.html

[Walter Roberson]

I do not know how waitbar() is implemented in R2014b and later.

In versions up to R2014a,

htext = findall(h, 'type','text');

then the message is the String property of htext(4) which is htext(end)

But waitbar(x,h,'updated message') is generally valid, and the error message you encounter should occur only if the arguments validate but the update fails with an exception. The code to do the update calls a private uiwaitbar.p (so I don't know when that might fail), and then if the string is provided tries to set() the String property of the title. It would be worth examining whether that text object still exists and if manually set()'ing the String works or not.

For example, I notice that by default the Interpreter property of the text object is 'tex', so if you were trying to use a string that happened to be malformed TeX then you could get a failure.

[Rosalie Martel]

I tried using very simple strings such as 'wait' and it did not work any more than a long sentence with spaces and accentuated characters. The strangest thing is that I don't get this error (or this problem) when using the waitbar in a 'for' loop elsewhere in my program... even with more complicated messages such as 'Analyzing data, please wait...'

[Stephen23]

What version of MATLAB are you using? This behavior may be related to a specific version...

At this point it might be worth using MATLAB's debugging tools and set a break-point to track down when this error occurs. Then check exactly what is happening when this error occurs, what value/s the associated variable have, and if the waitbar figure and text handles are correct.

[Rosalie Martel]

I am using R2014b. I will see what I can find using the debugger.