Why arrow head disappear

[epaalx]

As far as I can tell "add shapes" is a Union operation, which mean that all selected objects become united and nothing should disappear. However when I try to add shapes which were lines with arrowheads, the arrowheads disappear. Why?
Also, when I try the same with "join shapes" which is an XOR operation, in which case I'm expecting the lines to disappear altogether since they'd cancel each other out, they don't and also the arrowheads don't disappear, why?

[gwpriester]

Add Shapes probably has the wrong effect for what you are trying to do.

If you want to combine two lines into one line do this:

Select both lines then switch to the Shape Editor Tool (F4).

Drag one of the control points (where the two lines come together) away a short distance and then back to the end of the other line.

The cursor will change to display a small + to indicate the lines will now become one line.

Join Shapes does not do this.

It's a little messy but it is the way you join two line.

[epaalx]

Thanks.. but my aim is to create two arrowheads. If I join lines as you have, only one end will have the arrowhead.

[jvila]

Add shapes is for using with shapes, then you first have to select both lines and convert them to shape using the Arrange convert line to shape and then ctrl 1 (add shapes).
Best regards

[epaalx]

Javier, thank you very much.
It seems the answer to my question is simple... "Add Shapes" automatically converts lines into shapes, that's why the arrows disappear.
However, it seems that "Join Shapes" preserves lines that's why the arrowheads stay. So, "Join Shapes" seems to be an XOR for shapes but a "Union" of lines.

[gwpriester]

I understand the confusion.

You can add an arrowhead at each end by holding down the Ctrl key and double clicking on the arrowhead icon.

[The Alien]

Thanks.. but my aim is to create two arrowheads. If I join lines as you have, only one end will have the arrowhead.

Avoiding to go into the principles behind boolean operations, a more problem-oriented solution would be:
when you want to add the second arrowhead to the line, click and drag it from the line gallery to the empty end of your line. Or CTRL+double click the arrowhead. I believe that's what you're looking for?

[epaalx]

Thanks Gary and Alien.
BTW, why is it that when I apply a non-"Constant" stroke to a line, the arrowheads disappear?

[gwpriester]

That's just the way it works. I don't think there is a sinister reason for it.

If you want a stroked line or path that has an arrowhead, then create your arrow, clone the arrow and apply the stroke shape. Convert both lines to shape then combine shapes > add shapes.