MATLAB: Use timer to update text in pushbutton

guiMATLABpush button

Hello,

Is there a way for a pushbutton to change its text automatically after every 5 or so seconds? My plan is to use a matrix that will contain cells of words that will be displayed onto the pushbutton. For example it will start with the word " bent" then after five seconds, it will display " went". The changing text should not be dependent on the user pressing the button. If a pushbutton is not the way to go, then can you help me with what can work? I am very new to this whole GUI idea. Also, is it better to use GUIDE or write up my own code? Thank you.

Best Answer

Justin - using GUIDE is a good way to start designing your interface. Its GUI editor allows you to drag and drop components on to the "canvas", and it provides you with many of the callbacks that you would need to respond to push button events, menu choices, etc.

For your project, you can easily use a timer to update the text of a push button or a static text control. Either would suit your needs but perhaps there is a reason why you want a push button to be used.

In the _OpeningFcn of your GUI, you could create your five second timer as

 handles.timer = timer('Name','MyTimer',               ...
                       'Period',5,                     ...
                       'StartDelay',0,                 ...
                       'TasksToExecute',inf,           ... 
                       'ExecutionMode','fixedSpacing', ...
                       'TimerFcn',{@timerCallback,hObject}); 
 % Update handles structure
 guidata(hObject, handles);
 % start the timer
 start(handles.timer);

We save the timer handle to the handles structure in the event that we need to access it at a later time. We then start the timer (it is stopped when the GUI is closed) and rely on its callback to fire every five seconds. We define the callback as

 function timerCallback(hTimer, eventdata, hFigure)
 handles = guidata(hFigure);
 str = handles.myCellData{handles.strIdx};
 set(handles.pushbutton1,'String',str);
 handles.strIdx = handles.strIdx + 1;
 if handles.strIdx > length(handles.myCellData)
    handles.strIdx = 1; 
 end
 guidata(hFigure,handles);

Note the third parameter is hFigure which is the hObject from the _OpeningFcn. We use this (GUI) handle so that we can get the handles structure which contains our cell string data, the current index for where we are in the cell array, and the handles to all GUI controls (of which the pushbutton is of interest to us). We get the string, update the button text, increment the counter, and save the updated handles structure.

See the attached for an example. Try it, and see what happens!

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MATLAB: Run pushbutton automatically as soon as the GUI is visible without pressing the pushbutton

In the OpenFcn callback, create a timer object configured for a single execution, and have the callback for the timer object be a call to the name of the callback for the pushbutton, passing in the handle of the pushbutton, then [], and then the handles variable. But do it like this:

handles.push_timer = timer(... various arguments ...);
guidata(hObject, handles);   %store a copy of handles complete with the push_timer
handles.push_timer.TimerFcn = @(hObject, event) YourGUI_pushbutton1_Callback(handles.pushbutton1, [], handles);
start(handles.push_timer)

That is, do not set the TimerFcn callback to refer to handles until after you have already stored the timer object in handles. The timer() function permits you to configure TimerFcn as an option at the time you create the timer, but do not do that. If you do that, then the value of handles that makes it into the callback will not include the timer object and you would risk the timer being deleted before it gets used.

MATLAB: Issue with GUI.

Justin - I think what you can do is create another timer to periodically update the status bar, rather than relying a while loop that is called from within a hidden button (your pushbutton8).

For example, in the GuiTImerUpdateTextExample_OpeningFcn, you can instantiate your two timers, the original one and one for your progress bar as

 handles.timerQuery = timer('Name','MyQueryTimer',               ...
                            'Period',3,                     ...
                            'StartDelay',1,                 ...
                            'TasksToExecute',inf,           ... 
                            'ExecutionMode','fixedSpacing', ...
                            'TimerFcn',{@timerQueryCallback,hObject}); 
 handles.timerProgress = timer('Name','MyProgressTimer',        ...
                               'Period', 0.01,                   ...
                               'TasksToExecute',inf,            ...
                               'ExecutionMode', 'fixedSpacing', ...
                               'TimerFcn', {@timerProgressCallback, hObject});

The "query timer" will expire after three seconds, corresponding to the query that is asked of the user. The "progress timer* will expire every 10 milliseconds and will call the timerProgressCallback. Once we have created the timers, we can initialize your progress axes as

 % set the axes
 cla(handles.axes1);
 set(handles.axes1,'Visible','on','color',[.9 .85 .3]); %this will set the color of the patch
 axis(handles.axes1,[0,1,0,1]); %show only from x=0to 1 and y=0to1
 handles.hPatch = patch([0,0,0,0],[0,0,1,1],'g');
 axis(handles.axes1, 'off'); %do not show axis bars

Note how we create the patch and save its handle to the handles structure. We do this so that we can update this patch object rather than creating a new one every time we want to update the progress "bar".

We then save the updated handles structure and start the the query timer as

 guidata(hObject, handles);
 start(handles.timerQuery);

We don't start the other timer as we rely on the timerQueryCallback to do this for us as

 function timerQueryCallback(hTimer, eventdata, hFigure)
 handles = guidata(hFigure);
 % stop the progress timer
 stop(handles.timerProgress);
 % only set the progress timer to complete if there is text in pushbutton1
 % we pause for half a second to allow the progress bar to update
 if ~isempty(get(handles.pushbutton1,'String'))
    set(handles.hPatch,'XData',[0 1 1 0]);
    pause(0.5);
 end
 % etc.
 % reset the patch to show zero progress
 set(handles.hPatch,'XData',[0 0 0 0]);
 % use tic so that we can correctly update the progress
 tic;
 % start the timer
 start(handles.timerProgress);

That just leaves the timerProgressCallback which can be defined as

 function timerProgressCallback(hObject, eventdata, hFigure)
 handles = guidata(hFigure); 
 if ~isempty(handles)
    periodQuery    = get(handles.timerQuery,'Period');
    percentComplete = double(toc)/periodQuery;
    set(handles.hPatch,'XData',[0 percentComplete percentComplete 0]);
 end

We use toc and the period of the query timer to determine the progress and so how much of the patch to draw.

Try the above and see what happens! (See the attached for a working example.)

Best Answer

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MATLAB: Issue with GUI.

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