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# DeviceActivityMonitor

The object that monitors scheduled device activity.

```
@objc class DeviceActivityMonitor
```

## Overview

`DeviceActivityMonitor` provides the entry point into a device activity monitor extension.
You should subclass `DeviceActivityMonitor` and designate your subclass as the principal class of your app extension.

The following code implements `DeviceActivityMonitor` in an app:

```swift
class MyMonitorExtension: DeviceActivityMonitor {
  let store = ManagedSettingsStore()

  // You can use the `store` property to shield apps when an interval starts, ends, or meets a threshold.
  override func intervalDidStart(for activity: DeviceActivityName) {
      super.intervalDidStart(for: activity)

      // Shield selected applications.
      let model = MyModel()
      let applications = model.selectionToShield.applications
      store.shield.applications = applications.isEmpty ? nil : applications
   }
```

> Note: Shielding an app dims the app’s icon on the homescreen and applies an hourglass symbol.
> When the app launches, the system covers it with a view that your app can configure.

## Topics

### Configuring a Monitor

[`init()`](/documentation/DeviceActivity/DeviceActivityMonitor/init())

Creates a new monitor instance implemented by subclasses.

### Monitoring Scheduled Intervals

[`intervalDidEnd(for:)`](/documentation/DeviceActivity/DeviceActivityMonitor/intervalDidEnd(for:))

Indicates that the device activity interval ended.

[`intervalDidStart(for:)`](/documentation/DeviceActivity/DeviceActivityMonitor/intervalDidStart(for:))

Indicates that the device activity interval started.

[`intervalWillEndWarning(for:)`](/documentation/DeviceActivity/DeviceActivityMonitor/intervalWillEndWarning(for:))

Warns your app of an ongoing activity’s conclusion a specified time before the activity ends.

[`intervalWillStartWarning(for:)`](/documentation/DeviceActivity/DeviceActivityMonitor/intervalWillStartWarning(for:))

Warns your app of an upcoming activity a specified time before the activity starts.

### Monitoring Event Thresholds

[`eventDidReachThreshold(_:activity:)`](/documentation/DeviceActivity/DeviceActivityMonitor/eventDidReachThreshold(_:activity:))

Indicates that the activity reached its threshold.

[`eventWillReachThresholdWarning(_:activity:)`](/documentation/DeviceActivity/DeviceActivityMonitor/eventWillReachThresholdWarning(_:activity:))

Warns your app that an activity is about to reach its threshold.


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