Emulating a button push or a mouse click with Mathematica code

Question

I need to perform a long action with a button. I tried setting the DynamicEvaluationTimeout, but it seems it doesn't work for me. So I want to try using several buttons to compute pieces of the whole task and here's where my problem starts: How to tell Mathematica that a button should be pressed (or have its action performed) without actually pressing the button by user? Is there a way to emulate such a thing from within the code? I need to use the preemptive link, so Method -> "Queued" is not the solution I'm looking for.

Answer 1

One can come up with some messy method to evaluate a front-end button programmatically, but I think it is easier to separate the button functionality from the button itself, as listenerButtonFunction[]. Here I introduce a timer button that, if pushed, counts down simulating a long calculation. When it finishes, it switches the flag active to True. The second button has a Dynamic wrapper and thus it listens to the changes made to active: whenever active is set to True, the appearance of the listener button is changed. Now the functionality of the listener button is separated, so we can call it right after setting active = True in the first button, simulating the manual push of the listener button.

Note that I only used Method -> "Queued" to see how the timer goes down. If omitted, the listener still will be activated in due time. Also, the listener button can be pushed on its own.

active = False;
n = 0;
listenerButtonFunction[] := Print["Listener activated"];
Row@{Button["Timer", active = False; n = 100; 
   Do[Pause[.02]; n = n - 1, {i, 100}]; active = True; 
   listenerButtonFunction[], Method -> "Queued"], Spacer@5, Dynamic@n}
Dynamic@If[active,
  Button["Listener: ACTIVE", active = False, 
   Appearance -> {Automatic, "Pressed"}],
  Button["Listener: inactive", listenerButtonFunction[], 
   Appearance -> Automatic]
  ]

Update

The following method creates a button that is wrapped in Dynamic that listens to the state change of the switch active, which can be changed by either hitting the second button or waiting for the calculation of the first button to finish (just like above). The function of this second button is actually performed by the Dynamic wrapper whenever active becomes True. The Print statement is redirected by default to the Messages window, but if listenerFunction is e.g. a long calculation that does not print anything, this shouldn't matter.

active = False; n = 0;
listenerFunction[] := Print["Listener pushed"];

Row@{Button["First", active = False; n = 100; 
   Do[Pause[.005]; n = n - 1, {i, 100}]; active = True;, 
   Method -> "Queued"], Spacer@5, Dynamic@n}

Dynamic[If[active, listenerFunction[]]; 
 Button[If[active, "active", "inactive"], active = ! active]]