Locking the Legend even if the object is deleted

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Ruben Kopischke
Ruben Kopischke am 7 Feb. 2023
Kommentiert: Ruben Kopischke am 8 Feb. 2023
Hello,
I want the AutoUpdate of my legend to be "off" no matter whether I delete an object from the axes, but:
(since R2022b): If you delete an object from the axes, the legend updates to reflect the change regardless of whether this property (AutoUpdate) is set to "on" or "off".
I have programmed a simulation where the legend of the axes should stay as it is, no matter which objects you delete in the plot. Do you have any idea how I can implement this in newer versions of Matlab?
Warm regards,
Ruben

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Benjamin Kraus
Benjamin Kraus am 7 Feb. 2023
Bearbeitet: Benjamin Kraus am 7 Feb. 2023
As @Bjorn Gustavsson suggests, your best bet is to create proxy objects that are represented in the legend, but are not visible in the axes. @Bjorn Gustavsson says to place them "outside the visible area", but my recommendation is to use NaN data so they are not visible. For example:
% Objects with real data.
p = plot(magic(5));
% Create proxy objects with NaN data, which will now be rendered, but can
% be put into the legend.
hold on
pLegend = plot(NaN(5)); % Proxy objects with NaN data.
hold off
% Copy the SeriesIndex from the objects with real data to the proxy
% objects, which will make the colors and line styles match.
set(pLegend, {'SeriesIndex'},{p.SeriesIndex}');
% Use the proxy objects in the legend.
legend(pLegend);
% Now you can delete the real objects, but the proxy object will remain in the legend.
delete(p(3))
  5 Kommentare
Benjamin Kraus
Benjamin Kraus am 7 Feb. 2023
Bearbeitet: Benjamin Kraus am 7 Feb. 2023
I agree with @Bjorn Gustavsson that it would be better to selectively delete the objects you want to delete, rather than relying on cla. It wouldn't need to be a cell-array, as all graphics objects share a common matlab.mixin.Heterogeneous ancestor, and thus can be mixed together in a vector.
@Ruben Kopischke: Are you using cla or cla('reset')? Would it work for your workflow to set the HandleVisibility on the proxy objects to 'off'? This will work for cla but not cla('reset').
% Objects with real data.
p = plot(magic(5));
% Create proxy objects with NaN data, which will now be rendered, but can
% be put into the legend.
hold on
pLegend = plot(NaN(5)); % Proxy objects with NaN data.
hold off
% Copy the SeriesIndex from the objects with real data to the proxy
% objects, which will make the colors and line styles match.
set(pLegend, {'SeriesIndex'},{p.SeriesIndex}');
% Setting HandleVisible to 'off' will preserve the handles across a call to
% 'cla'.
set(pLegend, 'HandleVisibility', 'off')
% Use the proxy objects in the legend.
legend(pLegend);
% Now you can call 'cla' and still see the items in the legend.
cla
Ruben Kopischke
Ruben Kopischke am 8 Feb. 2023
Thank you all for your responses! I agree that my method is probably not that elegant, but with the last comment from @Benjamin Kraus I managed to make it work! Thanks a lot!

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Weitere Antworten (1)

Bjorn Gustavsson
Bjorn Gustavsson am 7 Feb. 2023
If you explicitly set the axis of the plot, then you can hide objects outside the visible are and use their handles for the legend. That way it doesn't matter what objects are still "alive" in your active plot. This is a fairly cludgy way to get around this, but I've found it useful to explain the meaning of different line-widths, line-styles when they display different properties across all lines.
  1 Kommentar
Ruben Kopischke
Ruben Kopischke am 7 Feb. 2023
Thats true, but if you delete the object from the axes, eg. with cla, the legend is updated, even if "AutoUpdate" is set to "off".

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