Hoe to implement a listener that deletes its calling object?

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royk 2020-7-12

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评论： Walter Roberson 2020-7-17

I would like to trigger DELETE of an IMAGES.ROI object upon ROIMoved event.

I am trying:

figure(1);clf;axis([0 100 0 100])
h = images.roi.Rectangle(gca,'position',uint16([10 20 10 20]));
addlistener(h,'ROIMoved',@(s,~)delete(s))

when the rectangle is moved it gets deleted (as desired) but it also issues an error:

Error using images.roi.Rectangle/MarkDirty

Value must be a handle.

Error in images.roi.internal.ROI/stopDrag

Error in images.roi.internal.ROI

What would be the right way for a listener to delete its object without invoking an error?

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Answer 1

Walter Roberson 2020-7-12

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编辑：Walter Roberson 2020-7-12

The right way would probably be not to do that at all.

Instead, put in a position constraint that prevents the ROI from moving and use a different method to delete the ROI if it must be deleted. In particular, do not delete the ROI from within a listener to the ROI (but you could delete the ROI from within a listener to mouse presses or key presses.)

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royk 2020-7-12

i guess... but am i not running into the same problem vis a vis deleting the timer (I guess the function called by the timer will have to delete the timer - is that allowed?)

Walter Roberson 2020-7-17

Yes, the callback function can delete the timer. But if you are doing this a bunch of time, it would be more efficient to just keep one timer around and change its callback (or properties), configure it to fire once, and start it as needed.

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Answer 2

royk 2020-7-12

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thanks Walter

What I want to do is is to specifically delete the ROI only after it is moved (the move is important becuase i want to record the new position of the ROI as an input before deleting it). Is there no way to delete an ROI based on its ROIMoved event?