BackgroundTaskAdd (Function)

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Operating mode
Handling background tasks
Specific features for Android
Specific features for iOS

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BackgroundTaskAdd (Function)

In french: TâcheEnArrièrePlanAjoute

Adds a new background task. This task will be performed periodically when the application is stopped or when it is running in the background.

Example

// Asks to process the incoming emails once a day
BackgroundTaskAdd(ProcBackgroundEmailProcess, 24*60)

PROCEDURE ProcBackgroundEmailProcess()
// Process the pending emails
n is int = ProcessIncomingEmails()
IF n > 0 THEN
// Notifies the user
notif is Notification
notif.Title = "Process completed"
notif.Message = StringBuild("%1 emails have been processed", n)
NotifAdd(notif)
END

Syntax

<Result> = BackgroundTaskAdd(<WLanguage procedure> [, <Time interval>])

<Result>: Integer

Identifier of added task,
0 if an error occurs. To get the details of the error, use ErrorInfo.

<WLanguage procedure>: Procedure name

WLanguage procedure ("callback" procedure) called when running the task.
This procedure must be a global procedure of project and it must expect no parameter. Otherwise, a fatal error will occur during the call to BackgroundTaskAdd.

<Time interval>: Optional integer

Minimum time interval (expressed in minutes) between two task executions. Used to guarantee that the task will not be run during this time interval. However, the system can increase the time interval according to several factors (important workload, low battery, etc.). Therefore, the real time interval can change and it can be quite long (several hours).
By default:
the time interval between two task executions is set to 1 hour.
the minimum time interval allowed is set to 15 minutes.
This parameter can correspond to:
an integer corresponding to the number of minutes,
a Duration variable,
Versions 23 and later
the duration in a readable format (e.g., '20min').
New in version 23
the duration in a readable format (e.g., '20min').
the duration in a readable format (e.g., '20min').

Remarks

Operating mode

Once added, the background task is automatically run by the system at regular time interval.

The task is persistent, it will continue to be run periodically when the application is stopped, even when the device is restarted.

If the task is triggered while the application is not started, the application will be run in background (without opening the first project window), the initialization process of project and the declaration process of classes and sets of procedures will be run before calling the procedure associated with the task.

The task will be run when the application is not started or when the application is in background. If the application is displayed in the foreground, its execution will be postponed.

As the task can be run in a secondary thread of the application, the code of the WLanguage procedure must not contain an access to the application's UI or open dialog boxes (via Info, Error, etc.). If the task must interact with the users, you can use notifications (Notifxxx functions).

Handling background tasks

To delete a task added by BackgroundTaskAdd, use BackgroundTaskDelete.
To list the added background tasks, use BackgroundTaskList.
InBackgroundMode is used to find out whether a procedure is run in "background" mode or not.

From the editor, you can specify that a procedure must be run in background task by enabling the corresponding option from the setting window of procedure automation. The task will be automatically added during the next application start: In this case, it is not necessary to call BackgroundTaskAdd.

Specific features for Android

If the task is to run while the device is in standby mode, it is recommended to ask the user to disable battery optimization for this application with SysBatteryOptimBackground.
Debugging:
For debugging purposes, you can force the execution of a background task via ADB by using the following command line:

adb shell cmd jobscheduler run -f <application> <id>

where:
- <application> corresponds to the package name of application as defined in the generation wizard (ex: com.mycompany.myapplication).
- <id> is the identifier of task to run (returned by BackgroundTaskAdd).
Required version:
Background tasks can only be added on devices running Android 5.0 or later (API level 21).
A fatal error occurs if the function is used with an earlier system version.
To determine the version of Android the application is running on, use SysAndroidVersion.
Required permissions:
The call to this function modifies the permissions required by the application.
Required permissions:
RECEIVE_BOOT_COMPLETED: allows an application to receive the ACTION_BOOT_COMPLETED that is diffused after the system finishes booting.
Once run, the task in background continues to operate as long as the application is installed.
The tasks in background are not called in the simulator.

Specific features for iOS

Runtime duration:
The background tasks have a total of 30 seconds to be run. If this time-out is exceeded, the application is directly stopped (this time-out can be reduced according to the system availability). Therefore, the task execution must be as fast as possible.
Practically, the system is using the execution time of task to define the real frequency at which it must be called.
Debugging:
You have the ability to debug the background tasks via Xcode, by triggering them manually via "Debug .. Simulate Background Fetch".
In order for the system to consider that the application can run background tasks, the application must perform network requests (calls to Webservices, HTTP requests, access to a HFSQL database, GPS, Email, ...). Indeed, iOS checks whether the application exploits data coming from the network.
The application must be able to run background tasks. On the device, in the "Device parameters .. Application name", the option "Refresh in background" must be checked.
When the application is specifically closed by a double press on the Home button and a swipe, the background procedure has less chances to be run.
The procedure will not be called anymore if the devices switches to "energy saving" mode.
The time-out between two procedure executions will be reduced if the device is plugged and connected to a WiFi network.
The frequency at which the application is enabled by the user will impact the call frequency of procedure.
The faster the request execution is, the shorter the time between two executions. In most cases, a long execution time of procedure means that the calls will be spaced out in time. The system gives priority to the procedures that consume less CPU.

Business / UI classification: Business Logic

Component: wd260android.jar