programming - Evaluation indicator for a notebook

I have a GUI with a number of TabView and other Manipulate controls. Sometimes clicking from one tab view to the other can take a while, and I would like to have a global "Please wait" indicator.

So one way is to implement it for each button or slider, but I would essentially like to have a visual indicator that will show if any cell in my notebook is being evaluated.

Any ideas or suggestions? (Have searched for answers here but I only found those related to progress bars for a specific calculation)

Answer

First, let's make a 'busy' animation

wait =
 DynamicModule[
    {i = 1, b = Import["http://ims.cartoninjas.net/manifoldtemplate/images/BusyAnimation.gif"]},
    Dynamic@Refresh[b[[i = Mod[i + 1, Length[b], 1]]], 
                    UpdateInterval -> .1, 

                    TrackedSymbols -> {}
    ]
 ]

Now, lets make a radio button bar to control the busy state in this demo:

Column[{"Waiting", RadioButtonBar[Dynamic[waiting], {True, False}]}]

Finally, here's the TabView. I use Overlay to overlay the busy animation in the busy state and prevent selection of the TabView:

g = {"Beethoven", "CastleWall", "Cone", "Cow"};
Overlay[
  {
    TabView[(# -> ExampleData[{"Geometry3D", #}] &) /@ g], 
    Dynamic@If[waiting, wait, "", ""]
  }, 
  {1, 2}, 
  Dynamic[If[waiting, 0, 1, 1]], 
  Alignment -> Top
]

It is the responsibility of your code to set and unset the busy state. Probably somewhere in the beginning and end, respectively, of a Dynamic piece of code in TabView.

---

Update As of Version 10.0.2 Animator can be used to create the busy animation. There are several kinds available, but one resembling the above can be generated using:

Animator[Appearance -> "Necklace"]