How to prevent the legend from updating in R2017a and newer?

Question

Since MATLAB R2017a, figure legends update automatically when adding a plot to axes. Previously, one could do this:

data = randn(100,4);
plot(data)
legend('line1','line2','line3','line4')
hold on
plot([1,100],[0,0],'k-')

to plot four data lines with a legend, and then add a black line for y=0. However, since R2017a, this leads to the black line being added to the legend, with the name "data1".

How do I prevent this line from being added to the legend, so that the code behaves like it did in older versions of MATLAB?

The only solution I have found so far on Stack Overflow is to remove the legend item after it has been added. The syntax is not pretty:

h = plot([1,100],[0,0],'k-'); % keep a handle to the added line
set(get(get(h,'Annotation'),'LegendInformation'),'IconDisplayStyle','off');

Answer 1

The release notes for MATLAB R2017a mention this change, and provide 4 different ways of handling the situation. These two methods are easiest to put into existing code:

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1: Turn off auto updating for the legend before adding the black line. This can be done at creation time:

legend({'line1','line2','line3','line4'}, 'AutoUpdate','off')

or after:

h = findobj(gcf,'type','legend');
set(h, 'AutoUpdate','off')

You can also change the default for all future legends:

set(groot,'defaultLegendAutoUpdate','off')

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2: Turn off handle visibility for the black line that you don't want added to the legend:

plot([1,100],[0,0],'k-', 'HandleVisibility','off')

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The IconDisplayStyle method is also shown here. However, they use the dot notation, which makes the syntax is a bit prettier:

h = plot([1,100],[0,0],'k-'); % keep a handle to the added line
h.Annotation.LegendInformation.IconDisplayStyle = 'off';