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The Background task sample provides a few examples of these triggers. In Scenario 1,
js/sample-background-task-with-condition.js, we can see the use of timeZoneChange along with the
userPresent condition (where BackgroundTaskSample is again a helper object in global.js):
BackgroundTaskSample.registerBackgroundTask(BackgroundTaskSample.sampleBackgroundTaskEntryPoint,
BackgroundTaskSample.sampleBackgroundTaskWithConditionName,
new Windows.ApplicationModel.Background.SystemTrigger(
Windows.ApplicationModel.Background.SystemTriggerType.timeZoneChange, false),
new Windows.ApplicationModel.Background.SystemCondition(
Windows.ApplicationModel.Background.SystemConditionType.userPresent));
This is clearly a case where I’d use another variable to not type the Windows.Application-
Model.Background namespace out every time, but at least you can’t make a mistake in reading this code!
In any case, the same sample, in Scenario 4 and js/global.js, also shows use of the servicing-Complete
trigger within a helper function registerServicingCompleteTask, which also checks if the task is already
registered:
"registerServicingCompleteTask": function () {
// Check whether the servicing-complete background task is already registered.
var iter =
Windows.ApplicationModel.Background.BackgroundTaskRegistration.allTasks.first();
var hascur = iter.hasCurrent;
while (hascur) {
var cur = iter.current.value;
if (cur.name === BackgroundTaskSample.servicingCompleteTaskName) {
BackgroundTaskSample.updateBackgroundTaskStatus(
BackgroundTaskSample.servicingCompleteTaskName, true);
return;
}
hascur = iter.moveNext();
}
},
// The servicing-complete background task is not already registered.
BackgroundTaskSample.registerBackgroundTask(
BackgroundTaskSample.servicingCompleteTaskEntryPoint,
BackgroundTaskSample.servicingCompleteTaskName,
new Windows.ApplicationModel.Background.SystemTrigger(
Windows.ApplicationModel.Background.SystemTriggerType.servicingComplete, false),
null);
In the sample, the tasks associated with these triggers are implemented in C#, within a WinRT
component found in the Tasks project of the sample’s solution. I won’t show the code here because
we’ll be looking at the general structure of WinRT components in Chapter 16. What it does
demonstrate, though, is that you can use a mixed-language approach for background tasks. In these
cases, the Entry Point field for the tasks in the manifest point to the C# class/method that implements
the background task, such as Tasks.ServicingComplete. If you go to the Background task sample page,
you can also download the C# and C++ versions of the sample to see even more structural variants.
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