DeviceWatcher Class

Definition

Namespace:

Windows.Devices.Enumeration

Enumerates devices dynamically, so that the app receives notifications if devices are added, removed, or changed after the initial enumeration is complete.

[Windows.Foundation.Metadata.ContractVersion(typeof(Windows.Foundation.UniversalApiContract), 65536)]
[Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
public sealed class DeviceWatcher

Inheritance

Object DeviceWatcher

Attributes

ContractVersionAttribute MarshalingBehaviorAttribute

Windows requirements

Device family	Windows 10 (introduced in 10.0.10240.0)
API contract	Windows.Foundation.UniversalApiContract (introduced in v1.0)

Examples

For complete examples in C# and C++, see the Device enumeration and pairing sample.

Remarks

An app calls Start to begin the search for devices. During this initial enumeration, the DeviceWatcher raises an Added event for each device that's found, until all devices are found. The DeviceWatcher raises an EnumerationCompleted event when the initial enumeration is complete, and continues to raise events if a device is added, updated, or removed.

The following diagram shows how the DeviceWatcher transitions between the states represented by DeviceWatcherStatus enumeration.

The Start method can only be called when the DeviceWatcher is in the Created, Stopped or Aborted state. The Status property indicates the DeviceWatcher state. When re-starting the watcher, wait for the Stopped event before calling Start.

Stop transitions the DeviceWatcher to the Stopping state and completes immediately. The watcher will transition to the Stopped state once all events that are already in the process of being raised have completed.

Apps may wait for the Stopped event if they need to know when the DeviceWatcher has stopped. Callers must wait for the Stopped event before they can call Start to restart the watcher. Callers may unsubscribe from events if they do not want to receive any additional events after Stop but do not want to wait for the Stopped event.

Note

An app must subscribe to all of the added, removed, and updated events to be notified when there are device additions, removals or updates. If an app handles only the added event, it will not receive an update if a device is added to the system after the initial device enumeration completes.

Properties

Status

The status of the DeviceWatcher.

Methods

GetBackgroundTrigger(IIterable<DeviceWatcherEventKind>)	Gets a DeviceWatcherTrigger object monitoring for changes to the list of devices.
Start()	Starts a search for devices, and subscribes to device enumeration events.
Stop()	Stop raising the events that add, update and remove enumeration results.

Events

Added	Event that is raised when a device is added to the collection enumerated by the DeviceWatcher.
EnumerationCompleted	Event that is raised when the enumeration of devices completes.
Removed	Event that is raised when a device is removed from the collection of enumerated devices.
Stopped	Event that is raised when the enumeration operation has been stopped.
Updated	Event that is raised when a device is updated in the collection of enumerated devices.

Applies to

See also

• Device enumeration and pairing sample