Using uiwait with wrndlg with modal property in a guide callback of a slider throws the code into chaos

Hello, In the callback of my slider which I created using guide, I want to insert a warndlg once a particular value has exceeded. I want to stop interaction with the main figure till the wrndlg box has been acknolwedged. I do so as: call a function which gives me an errorvalue 1 or 0 is the limit has exceeded.

function sliderElec1_Callback(hObject, eventdata, handles)
% hObject    handle to sliderElec1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'Value') returns position of slider
%        get(hObject,'Min') and get(hObject,'Max') to determine range of slider
[errorValue,errorMsg] = checkStimulationPara(hObject,handles);
if errorValue
    uiwait(warndlg(errorMsg, 'Warning', 'modal'));
    fid = fopen(handles.errorFileName,'at');  
    fprintf(fid,[datestr(now,'yymmdd') ' ' datestr(now,'HHMM'),': ']);
    fprintf(fid,['checkStimulationfn', '', errorMsg,'\n']);
    fclose(fid);
end

now, when i slide the slider across the set value for eg: 30, the dlg box goes crazy, opens and closes multiple times and goes into an infinte loop by increasing the slider value.

Any help will be greatly appreciated!

[Adam]

A modal warndlg shouldn't need a uiwait with it - a modal dialog incorporates this functionality anyway, though actually disabling a UI for interaction in Matlab is far more difficult that it should be!

[Darshan Shah]

Thanks Adam! I had tried that but I could still interact with the main figure and hence, moving the slider just made it call the callback repeatedly without acknowledging the dialog box!

[Jan]

The shown code does not cause a behavior like: "the dlg box goes crazy, opens and closes multiple times and goes into an infinte loop by increasing the slider value". Maybe the part, which increases the slider position is hidden inside checkStimulationPara?

[Dennis]

Do you have a custom function wrndlg or is this a typo?

[Darshan Shah]

function [errorValue,errorMsg] = checkStimulationPara(hObject,handles)

errorValue = 0;
errorMsg = [];

electrode = handles.activeElectrodeInd;
charge = get (eval(['handles.sliderElec',num2str(electrode)]), 'Value');
probeAmplitude  = round((charge/handles.Stim.phaseDuration) / (1200/127)*1000); 
if charge > handles.currentLFit.MaxStimCharge(electrode,1)
    errorValue = 1;
    probeAmplitude = probeAmplitude - 1;
    charge = handles.Stim.phaseDuration * (1200/127) * probeAmplitude/1000;
    set(eval(['handles.sliderElec',num2str(electrode)]), 'Value', charge);
    set(eval(['handles.sliderElec',num2str(electrode)]), 'Enable', 'off');
    if handles.Stim.phaseDuration >= 50
        errorMsg = 'Max Charge  and max possible phaseDuration reached. Please disable the electrode.';
    else
        errorMsg = 'Max Charge reached. Please increase the phaseDuration to stimulate further.';
    end
    fprintf([errorMsg, '\nDismiss the warning dialog box to enable the electrode again!\n']);
end
handles.textMCL.String = num2str(charge);
set (eval(['handles.textCharge',num2str(electrode)]), 'String', num2str(charge));
handles.currentLFit.MCL(electrode,1) = charge;
handles.currentLFit.MaxAmplitude(electrode,1) = probeAmplitude;
guidata(hObject,handles)

Here is the code for checkStimulationPara, I check the slider value for ablsolute max and then reset its value. Do you think that is causing the problem? I tried removing the reinitialization of the slider but the problem persists

[Darshan Shah]

Its a typo, I will correct it!

[Adam]

It is rarely a good idea to have code in a slider callback that changes the value of the slider. It can work, probably, but it is very counter-intuitive for usage as well as being easy to create situations like you seem, to be experiencing.

Don't use eval either. You can concatenate strings easily enough and use dynamic strings for field access with e.g.

handles.( ['textCharge',num2str(electrode)] )

[Darshan Shah]

Thank you Adam! Will Implement that!

[Adam]

If you are simply going to set the slider back to some other value why don't you just change the min or max of the slider to ensure that the user cannot select values out of the range in the first place? The general idea of a slider as oppose to just an edit box (or especially when combined with an edit box so you can see the slider current value) is that it defines the valid range for the values.

[Darshan Shah]

The reasoning was that I work with three ranges, and I set the slider to the max of the three ranges! So if the user goes above a particular limit, he has to change the range! I guess I could also change the MAX and MIN values for each range!

[Adam]

I don't know exactly what the design of your UI is, but standard UI components tend to come with standard expectations for users which you should think very carefully before over-riding and ignoring. One of the expectations of a slider is that it has been setup with a valid range so that the user should expect to be able to select any value within the slider's range, without having the underlying code jump on top of their selection and tell them it actually isn't allowed.

[Darshan Shah]

I agree with you Adam, but at the same time the option available to set parameters should allow you to set it without starting a circle of problems! I can agree that its not a smart idea to read and reset it.

[Adam]

If you are using a standard Matlab slider with a release callback rather than a continuous callback then it probably shouldn't cause problems, but it is something I always avoid doing as it is easy to create problems for yourself by 'pulling the rug out from under your feet'

[Darshan Shah]

I had no idea there were these variations! Thank you for pointing it out!