More efficient way to insert a push button in a figure and run a function or a command.

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Rafael Freire
Rafael Freire 2018-10-16
编辑： Jan 2018-10-17
Hi, I wrote the following function to plot x and y and when you press a button it calls the ginput of 2 coordinates and inserts the text of the result on the plot. The problem is that I had to create the ButtonDownFcn as an entire string to be evaluated. Ok, like that is working, but how can I be more efficient and call a function in a function to do that? Thank you very much and best regards Rafael
x=1:0.01:5;
y=sin(x);
function [ ] = Plot_with_ginput_buttonfn( x,y )
figure
plot(x,y)
% create a button to calculate the difference between 2 points
h = uicontrol('Position',[5 5 150 30],'String','Calculate xdiff',...
'Callback','uiresume(gcbf)');
h.Enable = 'Inactive';
h.ButtonDownFcn=['[ppm, intensity]=ginput(2);' ...
'J=abs(diff(ppm))*600;'...
'Jstr=sprintf(''J=%.1fHz'', J);' ...
'meanppm=abs(mean(ppm));' ...
'ppmstr=sprintf(''%.3f'', meanppm);'...
'text(meanppm, mean(intensity), {[''\delta'' ppmstr]; Jstr});'];
end
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Rafael Freire
Rafael Freire 2018-10-16
编辑：Rafael Freire 2018-10-16
Now it is working fine, I added the x,y in the nested function
function Jcal(x,y)
and it works. Why? Do I need to add all arguments in the nested function as well?
Steven Lord
Steven Lord 2018-10-16
As stated in the Callback Function Syntax section on this documentation page:
"Graphics callback functions must accept at least two input arguments:
  • The handle of the object whose callback is executing. Use this handle within your callback function to refer to the callback object.
  • The event data structure, which can be empty for some callbacks or contain specific information that is described in the property description for that object."

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采纳的回答

Jan
Jan 2018-10-16
编辑：Jan 2018-10-17
What about using the Callback instead of the ButtonDownFcn?
function Plot_with_ginput_buttonfn( x,y )
figure
plot(x,y)
% create a button to calculate the difference between 2 points
h = uicontrol('Position',[5 5 150 30],'String','Calculate xdiff',...
'Callback', @JCal);
function JCal(ButtonH, EventData)
[ppm, intensity] = ginput(2);
J = abs(diff(ppm))*600;
Jstr = sprintf('J=%.1fHz', J);
meanppm = abs(mean(ppm));
ppmstr = sprintf('%.3f', meanppm);
text(meanppm, mean(intensity), {['\delta' ppmstr]; Jstr});
end
end
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Adam
Adam 2018-10-17
编辑：Adam 2018-10-17
Callbacks must have 2 input arguments (as per the link Steven Lord shared above), which I usually call src and evt (but you can call them what you want, as you see). They represent the source object (the control that triggered the callback) and the event data which is usually useless, but for a small number of components carries useful information (e.g. tab group tab selected event tells you which tab you came from and which you are going to).
After that Matlab doesn't care what arguments you include except for the usual function rules that if you refer to something in the function that hasn't been declared or passed in as an argument it will error.
You can define any function with 15 arguments and use none of them in the function body if you really wish though!
Rafael Freire
Rafael Freire 2018-10-17
编辑：Rafael Freire 2018-10-17
Thank you very much. I read the links that Steven and Stephen shared, but I still had some doubts. Now, your comment clarifies everything to me. Now I got it. Thanks for all of you for helping me.

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