Szerkesztés

Megosztás a következőn keresztül:

Use a maintenance trigger

  • Cikk

Important APIs

Learn how to use the MaintenanceTrigger class to run lightweight code in the background while the device is plugged in.

Create a maintenance trigger object

This example assumes that you have lightweight code you can run in the background to enhance your app while the device is plugged in. This topic focuses on the MaintenanceTrigger, which is similar to SystemTrigger.

More information on writing a background task class is available in Create and register an in-process background task or Create and register an out-of-process background task.

Create a new MaintenanceTrigger object. The second parameter, OneShot, specifies whether the maintenance task will run only once or continue to run periodically. If OneShot is set to true, the first parameter (FreshnessTime) specifies the number of minutes to wait before scheduling the background task. If OneShot is set to false, FreshnessTime specifies how often the background task will run.

Note

If FreshnessTime is set to less than 15 minutes, an exception is thrown when attempting to register the background task.

This example code creates a trigger that runs once an hour.

uint waitIntervalMinutes = 60;
MaintenanceTrigger taskTrigger = new MaintenanceTrigger(waitIntervalMinutes, false);

uint32_t waitIntervalMinutes{ 60 };
Windows::ApplicationModel::Background::MaintenanceTrigger taskTrigger{ waitIntervalMinutes, false };

unsigned int waitIntervalMinutes = 60;
MaintenanceTrigger ^ taskTrigger = ref new MaintenanceTrigger(waitIntervalMinutes, false);

(Optional) Add a condition

  • If necessary, create a background task condition to control when the task runs. A condition prevents your background task from running until the condition is met - for more information, see Set conditions for running a background task

In this example, the condition is set to InternetAvailable so that maintenance runs when the Internet is available (or when it becomes available). For a list of possible background task conditions, see SystemConditionType.

The following code adds a condition to the maintenance task builder:

SystemCondition exampleCondition = new SystemCondition(SystemConditionType.InternetAvailable);

Windows::ApplicationModel::Background::SystemCondition exampleCondition{
    Windows::ApplicationModel::Background::SystemConditionType::InternetAvailable };

SystemCondition ^ exampleCondition = ref new SystemCondition(SystemConditionType::InternetAvailable);

Register the background task

  • Register the background task by calling your background task registration function. For more information on registering background tasks, see Register a background task.

The following code registers the maintenance task. Note that it assumes your background task runs in a separate process from your app because it specifies entryPoint. If your background task runs in the same process as your app, you do not specify entryPoint.

string entryPoint = "Tasks.ExampleBackgroundTaskClass";
string taskName   = "Maintenance background task example";

BackgroundTaskRegistration task = RegisterBackgroundTask(entryPoint, taskName, taskTrigger, exampleCondition);

std::wstring entryPoint{ L"Tasks.ExampleBackgroundTaskClass" };
std::wstring taskName{ L"Maintenance background task example" };

Windows::ApplicationModel::Background::BackgroundTaskRegistration task{
    RegisterBackgroundTask(entryPoint, taskName, taskTrigger, exampleCondition) };

String ^ entryPoint = "Tasks.ExampleBackgroundTaskClass";
String ^ taskName   = "Maintenance background task example";

BackgroundTaskRegistration ^ task = RegisterBackgroundTask(entryPoint, taskName, taskTrigger, exampleCondition);

Note

For all device families except desktop, if the device becomes low on memory, background tasks may be terminated. If an out of memory exception is not surfaced, or the app does not handle it, then the background task will be terminated without warning and without raising the OnCanceled event. This helps to ensure the user experience of the app in the foreground. Your background task should be designed to handle this scenario.

Note

Universal Windows Platform apps must call RequestAccessAsync before registering any of the background trigger types.

To ensure that your Universal Windows app continues to run properly after you release an update to your app, you must call RemoveAccess and then call RequestAccessAsync when your app launches after being updated. For more information, see Guidelines for background tasks.

Note

Background task registration parameters are validated at the time of registration. An error is returned if any of the registration parameters are invalid. Ensure that your app gracefully handles scenarios where background task registration fails - if instead your app depends on having a valid registration object after attempting to register a task, it may crash.