Dynamic block Contraints

[vboire9DBSV]

What constraints or group of constraints would I require in order to be able to move the red line while always being connected to the 2 green lines? And have the green lines keep their locations. File attached. 

[Libbya]

Short answer is 'none'.  Using constraints to accomplish that would be the hard and problematic way to do it, IMO.

[vboire9DBSV]

Any suggestions?

[Libbya]

Well, I was trying to record a screencast of the 'easy' way to do it, but something is not right with your file.  The angle offset for move/stretch angles are messed up.  They seem to default to 90 instead of 0 as they should and when set to 0 they behave incorrectly.  I did a recover on the file and it showed errors.  I'll make a similar screencast from a fresh file and hopefully you can apply the technique as needed.  Just a minute.  

[Libbya · Accepted solution]

I add a move action that has 0 angle offset and 1 for distance multiplier and move the line.  I then add a stretch action to each end of the line.  I adjust the angle offset so the stretch is perpendicular to the parameter movement.  I offset the line 1 unit and use quickcalc to get the adjusted stretch distance per 1 unit of parameter movement.  Hope that helps and makes sense.  See screencast.

[vboire9DBSV]

Thank you. My mind was convinced it should be a constraints function. Very much appreciated.