Tasker: Flow Control

Flow Control

Overview

Task flow control is based on the following elements:

variable values
conditions on individual actions
If / Endif actions for conditional grouping of following actions
Goto action (jumping around within a task).
Perform Task action (calling other tasks as subroutines)
Stop action (terminate task immediately)

On the Wiki there is a detailed example of processing a file contents [External Link].

Tip: if you accidentally create a task that never ends when experimenting with loops, use the KillAll button in the Task Edit screen to end it manually.

Conditions

Every action can have a condition associated with it (do this in the Action Edit screen). If the condition does not match, the action will be skipped.

A condition consists of an operator ('equals' etc) and two parameters. The possible operators are:

Matches (~)
The right parameter is a pattern which the left parameter is matched against.
Not Matches (!~)
As above, but the match must fail for the action to be executed.
Less Than (<)
Both parameters (after variables are substitued) must be numbers or mathematical expressions and the first must be less than the second e.g. 3 < 6. Expressions can use the four basic operators, which bind in the order / * - + e.g. if %COUNT is 3, then %COUNT * 20 + 5 is 65. Operations are performed in floating-point arithmetic.
Greater Than (>)
As above, but the first parameter must evaluate to more than the second.
Equals (=)
As above, but the two parameters must be numerically equal.
Not Equals (!=)
As above, but the two parameters must be not numerically equal.

Expressions which are not mathematically valid e.g. I Am The Walrus > 5 give a warning and evaluate to false when used with a mathematical operator.

Until Loop

Goal: perform a Task X until some condition is met (at least once)

1.	Action One	...
2.	Action Two	...
3.	Goto Action 1 If %QTIME < 20	Return to action 1 if runtime < 20

Result: Action One and Action Two are performed until %QTIME contains the value 20 or more i.e. until the task has been running for 20 seconds.

While Loop

Goal: perform a Task X while some condition is met.

1.	Stop If %FRUIT != Apple	Stop task if it's not crunchy, otherwise go to next action
2.	Action One	...
3.	Action Two	...
4.	Goto Action 1	Go back and see if we're still crunchy

Result: Action One and Action Two are performed while %FRUIT contains the value Apple.

Counter Loop

Goal: perform a Task X a set number of times.

1.	Variable Set %COUNT, 0	Initialize the counter
2.	Action One	...
3.	Action Two	...
4.	Variable Add %COUNT, 1	Add one to %COUNT
5.	Goto Action 2 If %COUNT < 10	Return to action 2 if count < 10

Result: after initialization of %COUNT to 0, the task loops around the actions from 2-5 until %COUNT reaches 10, at which point the condition on the Goto Action fails and the end of the task is reached.

If / Then / Else Condition

Goal: perform certain Tasks if conditions are met, otherwise perform a different task.

1.	Perform Task X, Stop = On If %FRUIT = Apple	Stop and do task X if crunchy fruit, otherwise next action
2.	Perform Task Y, Stop = On If %FRUIT = Banana	Stop and do task Y if squashy fruit, otherwise next action
3.	Perform Task Z	Other fruit: task Z

Subroutines

To call another task, use the Perform Task action. To use it as a subroutine, you just need to ensure that the priority of the calling task is less than the priority of the called task (more info: scheduling).

Scheduling

Be sure to read the information on Task Scheduling if you plan to have tasks sticking around for a while in a loop.