Manipulate evaluation sequence

Question

Manipulate doesn't always evaluate in the order I expect it to. What is the evaluation sequence for Manipulate and other functions involved with the front end? I have seen the evaluation sequence for kernel only functions, but that was for a reference for Mathematica 3, and doesn't deal with the front end.

Answer 1

According to my previous experiences and this post, the sequence goes like this (please feel free to correct me in this post):

1. From the documentation:

   Manipulate generates a DynamicModule object, with the variables u, v, etc. specified as local.

   That is, first Manipulate wraps its result into DynamicModule, then...

2. ...gives unique names to local variables (as it is a scoping construct).
3. Next, the body of Manipulate is evaluated in standard order.
4. The output cell is created by evaluating the result of the DynamicModule (or the Manipulate).
5. If there was any Initialization :> init inside Manipulate, it is now evaluated "when the result is first displayed in a particular session".
6. If there is any Deinitialization :> deinit inside Manipulate and the dynamic output cannot be displayed any more, deinit is evaluated.

Contraintuitively, Initialization is called almost ultimately which caused me some frustration over time.

To understand how to load a package with your dynamic content by Needs, see my answer here.