dynamic block-stretching?

I have created a simpledynamic blocks which represents a (simple)elevation of door. I have modified the block so i can stretch it but there is a line that goes from the top left to the middle right & then back to the bottom left of the rectangle(that represents the door). this line represents the way the door opens.

I want the point of the line that is at the middle to stay in the middle when i stretch the door height, how is this done?

I have searched the help but not had any luck.

Go here, read part 3, page 6. Doesn't sound like the simplest of dynamic block actions (I haven't tried it yet), but doesn't sound too bad either.

The Multiplier/Offset option is a great little tool. You should also investigate the Lookup parameters to ensure that standard sizes are used.

The "Best Practices" paper mentioned by Kate M is probably one of the best resources around, but some of it won't make sense until you've had a bit of practice.

- Jason.

add an extra stretch action linked to your linear parameter that increases the door height, but select only the 'door direction' lines.

Make sure you put your stretch frame around the points on the line that you want to remain central to the door frame.

Next, go into the properties of this stretch action and change the distance multiplier to .5, this will make the centre point of the door direction lines move with the door height, but only half the distance, which will always keep the centre point of these lines central to the door itself.

hope this helps, it isnt the easiest thing to explain without a drawing but give me a shout if you need any more help!

edit: just seen the date of your post, bit late methinks but still, its there if anyone else needs some help!