Module[Monitor[ ... ]] doesn't work when called by Manipulate?

Question

My example function

progressFunction[time_] := Module[{t}, Monitor[For[t = 0, t <= time, t++, Pause[1]], ProgressIndicator[t, {0, time}]]]

does exactly what I intend when I call it directly:

progressFunction[5]

(displays progress bar increasing from 0% to 100% over 5 seconds).

But when this function is called from within Manipulate:

Manipulate[progressFunction[time], {time}]

the Monitor cell displays:

Interestingly, when I copy/paste the above text into a new cell, it displays correctly in the new cell.

Any idea what's going on and how to fix this? This is pretty annoying because my real Manipulate expression calls functions that take a long time to complete, so I have implemented Monitor on all of them, but they all become useless under Manipulate.

Answer 1

I'm not sure exactly how you want the interface. Here's way to monitor the progress but without Monitor:

ClearAll[progressFunction];
progressFunction[time_, t_] := Module[{},
   If[time > 0,
    For[t = 0, t <= time, t++, Pause[1]]
    ];
   t = 0;
   ];

Manipulate[
 progressFunction[time, Unevaluated@progress];
 {time, progress},
 {{time, 0}, InputField},
 {{progress, progress}, 0, time,
  Replace[Hold[##], 
    Hold[Dynamic[p_], i__] :> Dynamic@ProgressIndicator[p, i]] &},
 TrackedSymbols :> {time}]

Here's a way using Monitor but it's not as good since it evaluates twice. I cannot be sure whether that would happen in your actual use case, though.

ClearAll[progressFunction];
progressFunction[time_, t_] :=
  Monitor[
   For[t = 0, t <= time, t++, Pause[1]],
   ProgressIndicator[t, {0, time}]
   ];

Manipulate[
 progressFunction[time, Unevaluated@timer];
 {time, timer},
 {time, InputField}, {{timer, timer}, None},
 TrackedSymbols :> {time}]