Evaluation leak from Dynamic exported to NB format

Question

This is closely related to the recent: Creating self destructing notebook.

However the answer doesn't work in my case.

A small example is:

ExportString[Dynamic[Print[1]], "NB"]

and it prints 1 :-(

A real word case is to save a notebook without triggering dynamics inside:

nb = Notebook[{
   Cell @ BoxData @ ToBoxes @ DynamicModule[{},
       "whatever",
       Initialization :> {Print["initialization"]}
   ]},
   NotebookDynamicExpression :> Refresh[Print["dynamicExpression"], None]
];

Now, I want to save a notebook without prompting Dynamic print statements.

Export[
 FileNameJoin[{$HomeDirectory, "Desktop", "silent.nb"}],
 nb, "NB"
]

Can I prevent that?

Answer 1

Explanation

It is not a leak if this is intended, right? It happens because MMA is trying to determine ImageSizeCache for DynamicBox that will be generated.

ImageSizeCache is explained in

tutorial / AdvancedDynamicFunctionality / ImageSizeCache in Dynamic

My approach to fix it

This tutorial will teach us the the fix is to use a fixed value of ImageSizeCache and SynchronousUpdating -> Automatic.

The problem is that one may want to have a better control over SynchronousUpdating at the end.

To circumvent that we can add additional Dynamic which won't be triggered more than needed and will alow to preserve inner Dynamic's options:

ExportString[
  Dynamic[
    Dynamic[
      Print@1
    ],
    SingleEvaluation    -> True,
    SynchronousUpdating -> Automatic,
    ImageSizeCache      -> {28., {0., 9.}}
  ],
  "NB"
]

WRI support response

I felt like it is something very fundamental for working with UI developement in MMA so I asked WRI Support to help me.

It took a while but I received an answer, which is to suspend DynamicUpdating when Export takes place.

[...]

For the effect you want, turn off the global DynamicUpdating option for the fronend just before the call to Export, and then clear that setting after Export.

For example:

CurrentValue[$FrontEnd, DynamicUpdating] = False;
Export[file, nbexpr] 
CurrentValue[$FrontEnd, DynamicUpdating] = Inherited;

[...]

One should know it may not work well with Dynamics that have UpdateInterval option: Toggling DynamicUpdating aborts dynamics with UpdateInterval