Adding legend to plot window before actually plotting

Question

Thomas 2014-1-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/113218-adding-legend-to-plot-window-before-actually-plotting

回答： Walter Roberson 2014-1-22

I have written a timer object function which updates a plot every 10ms. The plot window is all set up before the first timerFCN iteration. It basically plots 2 sets of data (one red line and one blue line with respect to time). I need to add a legend to this plot. Is there somehow i create a custom legends (i.e. define my own linestyle and linecolour for the legend). Since it only starts plotting once the first timerFcn runs, if i try to add a legend before this, it comes up with Warning: Plot empty.

I could add the legend in the timerFcn code section, but since its running every 10ms, just running that one extra line will cause my code to run a bit slower, which i cant have.

Thanks

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Answer 1

Walter Roberson 2014-1-22

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https://ww2.mathworks.cn/matlabcentral/answers/113218-adding-legend-to-plot-window-before-actually-plotting#answer_121765

Create the two lines ahead of time, with the appropriate color and marker, and with [] as their XData and YData. You can then legend(). After that, as you go, update the XData and YData properties of the two lines to reflect the incoming data.