Any good advice on understanding when/how to use parametrics in dynamic blocks?

[Anonymous]

I don't know of any good tutorials that go over when to use parametrics in dynamic blocks and when not to.  I come from MDT, IV, and Solidworks so I'm used to parametric sketching and I'm having issues with understanding dynamic blocks as a result.  What's the advantage of one vs the other. 

Case in point I don't know what the point of the stretch command is (or why it takes 3-4 clicks to setup) if I can apply a dimension and click/drag that dimension.  Same thing for a rotating angle.

[edwin.prakoso]

There are two ways to create a dynamic block: it works by action or by size. 

The actions (the stretch, mirror, array, etc) can modify the block. If you want to modify your dynamic block by action, then use parameters and action. It means you can change it by following AutoCAD users logic. 

If I want to make it longer then I stretch it. If I want to make it bigger, then I scale it. If I want to flip it, then I use mirror command.

The constraints method is similar to the parametric design in SolidWorks or other parametric design software. You use it if you want to get a specific size or angle. You don't need to think about what command you should use. 

Which one is better? It depends on the block. You might want to read this too: http://www.cad-notes.com/dynamic-block-action-vs-dynamic-block-parameters/

[Libbya]

My best advice (based on a decent level of proficiency with both dynamic parameters/actions and parametric constraints is to use dynamic parameters/actions whenever they can accomplish the task and use parametric constraints only as a last resort when they can accomplish something the dynamic parameters/actions cannot do.

The reasons I have for this view are multifold.  

The biggest reason is that the behavior of constraints is not consistent, e.g. 99 times when you alter a dimension the line stretches and the 100th time, the whole block implodes into a non-recoverable state.  The inconsistent behavior is often dependent on how fast you move a grip.  On the other hand, the action of dynamic parameters/actions is ROCK SOLID.  99.9% of the issues with dynamic parameters/actions are caused by mistakes made by the creator of the block.  Trying to use constraints to make a block dynamic is like trying to move a noodle in a straight line by pushing it from the back - it squishes out every direction except the way you want it to go.  Using dynamic parameters/actions is like grabbing the front of the noodle and pulling it.  It goes exactly where you want it to go and intrinsically stays straight just from the nature of the action.

The other reasons against using constraints are that the block action takes longer to process and blocks made with constraints will require more memory and larger files than the same block made using dynamic parameters/actions.