How to abort running evaluation?

Question

I would like to implement a "Stop" Button into a program that basically consists of a loop. Unfortunately I do not how to interrupt the running evaluation. Minimal Example:

Grid[{
{Button["Start", {i = 1; While[i < 10, Print[i]; Pause[1]; i++]}, 
Method -> "Queued"]},
{Button["Stop", {Quit[]}, Method -> "Queued"]}
}]

In this Case the "Stop" Button evaluates after the Evaluation from the "Start" Button has finished. Is there any possibility to quit the calculation immediately by a "Stop" Button? Thanks in advance for any Help!

Answer 1

From my perspective, the best way to interrupt a computation is with the menu command Evaluation/Abort Evaluation, or from the keyboard, as described here.

However, if using Button is desirable for other reasons, delete Method -> "Queued" so that the "Stop" code is executed immediately. Be aware, though, that Quit[] terminates the Kernel, losing definitions and the like; see its documentation. Instead, use Interrupt. In either case , Mathematica will stop responding for several seconds, then beginning responding again. With these changes, your code becomes

Grid[{{Button["Start", {i = 1; While[i < 10, Print[i]; Pause[1]; i++]}, 
    Method -> "Queued"]}, {Button["Stop", Interrupt[]]}}]

Note that Abort[] is ineffective in the code above.

Addendum

However, if the goal literally is to escape on command from a loop, like that in the test problem, Abort[], Break[], and a few other functions can be used, depending on the details of the loop. For instance,

Dynamic[break = False]
Grid[{{Button["Start", {i = 1; While[i < 10, If[break == True, Abort[]]; Print[i]; Pause[1]; 
  i++]}, Method -> "Queued"]}, {Button["Stop", Dynamic[break = True]]}}]

The advantage of this approach is that Mathematica does not temporarily become unresponsive when "Stop" is clicked. The disadvantage is that the loop terminates only where If[break == True, Abort[]] is encountered, although it can be located in multiple places in a large loop. Also, Dynamic can be temperamental.