How to detect if a plot has already existed?

Question

Leon 2019-10-23

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/487012-how-to-detect-if-a-plot-has-already-existed

评论： Leon 2019-10-23

What I want to do is to plot my sampling stations on a map. The map is pre-plotted . I want to delete the previous sampling stations (h1 handle) if they already exist and then plot the new sampling stations.

Below is my code:

if isexist(h1)
    delete(h1);
end
hold(app.mapPlot, 'on');
h1 = plot(app.mapPlot, lonlat(:,1), lonlat(:,2), 'o', 'color', 'b','markersize', 5);

Unfortunately, I got the below error:

Unrecognized function or variable 'h1'

Any idea on how to make this work?

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Answer 1

Joe Vinciguerra 2019-10-23

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https://ww2.mathworks.cn/matlabcentral/answers/487012-how-to-detect-if-a-plot-has-already-existed#answer_397890

在 MATLAB Online 中打开

Try this... (note I'm using "exist" instead of "isexist")

clear % I'm starting with no 'h1'. This checks the "False" condition
if exist('h1')
    delete(h1); % if 'h1' is a thing, delete it
end
h1=plot([5 8],[12 11]); % now there is an 'h1' either way
hold on; % I insertered this to match your application
pause(3); % wait a few seconds to verify it visually
% Let's do it again to check the "True" condition
if exist('h1')
    delete(h1); % if 'h1' is a thing, delete it
end
h1 = plot([1 2],[2 4]); % still works

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Joe Vinciguerra 2019-10-23

I'm not as familiar with the app designer, but I'll try to help.

Are you sure it's really not deleting? Or is it deleting and replotting the same data quick enough that you don't notice?

Try another command instead of "delete". Perhaps "close"?

Leon 2019-10-23

在 MATLAB Online 中打开

Many thanks! Weird enough, if I put the below code after the plot, it will delete the current sampling stations as expected. However, if I move it ahead of the plotting routine, the previously plotted sampling stations will remain there.