Class Observer

Provides a set of static methods for creating observers.

Inheritance

Object

Observer

Inherited Members

Object.Equals(Object)

Object.Equals(Object, Object)

Object.GetHashCode()

Object.GetType()

Object.MemberwiseClone()

Object.ToString()

Object.ReferenceEquals(Object, Object)

Namespace: System.Reactive

Assembly: System.Reactive.Core.dll

Syntax

public static class Observer

Methods

AsObserver<T>(IObserver<T>)

Hides the identity of an observer.

Declaration

public static IObserver<T> AsObserver<T>(this IObserver<T> observer)

Parameters

Type	Name	Description
IObserver<T>	observer	An observer whose identity to hide.

Returns

Type	Description
IObserver<T>	An observer that hides the identity of the specified observer.

Type Parameters

Name	Description
T	The type of the elements received by the source observer.

Exceptions

Type	Condition
ArgumentNullException	observer is null.

Checked<T>(IObserver<T>)

Checks access to the observer for grammar violations. This includes checking for multiple OnError or OnCompleted calls, as well as reentrancy in any of the observer methods. If a violation is detected, an InvalidOperationException is thrown from the offending observer method call.

Declaration

public static IObserver<T> Checked<T>(this IObserver<T> observer)

Parameters

Type	Name	Description
IObserver<T>	observer	The observer whose callback invocations should be checked for grammar violations.

Returns

Type	Description
IObserver<T>	An observer that checks callbacks invocations against the observer grammar and, if the checks pass, forwards those to the specified observer.

Type Parameters

Name	Description
T	The type of the elements received by the source observer.

Exceptions

Type	Condition
ArgumentNullException	observer is null.

Create<T>(Action<T>)

Creates an observer from the specified OnNext action.

Declaration

public static IObserver<T> Create<T>(Action<T> onNext)

Parameters

Type	Name	Description
Action<T>	onNext	Observer's OnNext action implementation.

Returns

Type	Description
IObserver<T>	The observer object implemented using the given actions.

Type Parameters

Name	Description
T	The type of the elements received by the observer.

Exceptions

Type	Condition
ArgumentNullException	onNext is null.

Create<T>(Action<T>, Action)

Creates an observer from the specified OnNext and OnCompleted actions.

Declaration

public static IObserver<T> Create<T>(Action<T> onNext, Action onCompleted)

Parameters

Type	Name	Description
Action<T>	onNext	Observer's OnNext action implementation.
Action	onCompleted	Observer's OnCompleted action implementation.

Returns

Type	Description
IObserver<T>	The observer object implemented using the given actions.

Type Parameters

Name	Description
T	The type of the elements received by the observer.

Exceptions

Type	Condition
ArgumentNullException	onNext or onCompleted is null.

Create<T>(Action<T>, Action<Exception>)

Creates an observer from the specified OnNext and OnError actions.

Declaration

public static IObserver<T> Create<T>(Action<T> onNext, Action<Exception> onError)

Parameters

Type	Name	Description
Action<T>	onNext	Observer's OnNext action implementation.
Action<Exception>	onError	Observer's OnError action implementation.

Returns

Type	Description
IObserver<T>	The observer object implemented using the given actions.

Type Parameters

Name	Description
T	The type of the elements received by the observer.

Exceptions

Type	Condition
ArgumentNullException	onNext or onError is null.

Create<T>(Action<T>, Action<Exception>, Action)

Creates an observer from the specified OnNext, OnError, and OnCompleted actions.

Declaration

public static IObserver<T> Create<T>(Action<T> onNext, Action<Exception> onError, Action onCompleted)

Parameters

Type	Name	Description
Action<T>	onNext	Observer's OnNext action implementation.
Action<Exception>	onError	Observer's OnError action implementation.
Action	onCompleted	Observer's OnCompleted action implementation.

Returns

Type	Description
IObserver<T>	The observer object implemented using the given actions.

Type Parameters

Name	Description
T	The type of the elements received by the observer.

Exceptions

Type	Condition
ArgumentNullException	onNext or onError or onCompleted is null.

NotifyOn<T>(IObserver<T>, IScheduler)

Schedules the invocation of observer methods on the given scheduler.

Declaration

public static IObserver<T> NotifyOn<T>(this IObserver<T> observer, IScheduler scheduler)

Parameters

Type	Name	Description
IObserver<T>	observer	The observer to schedule messages for.
IScheduler	scheduler	Scheduler to schedule observer messages on.

Returns

Type	Description
IObserver<T>	Observer whose messages are scheduled on the given scheduler.

Type Parameters

Name	Description
T	The type of the elements received by the source observer.

Exceptions

Type	Condition
ArgumentNullException	observer or scheduler is null.

NotifyOn<T>(IObserver<T>, SynchronizationContext)

Schedules the invocation of observer methods on the given synchonization context.

Declaration

public static IObserver<T> NotifyOn<T>(this IObserver<T> observer, SynchronizationContext context)

Parameters

Type	Name	Description
IObserver<T>	observer	The observer to schedule messages for.
SynchronizationContext	context	Synchonization context to schedule observer messages on.

Returns

Type	Description
IObserver<T>	Observer whose messages are scheduled on the given synchonization context.

Type Parameters

Name	Description
T	The type of the elements received by the source observer.

Exceptions

Type	Condition
ArgumentNullException	observer or context is null.

Synchronize<T>(IObserver<T>)

Synchronizes access to the observer such that its callback methods cannot be called concurrently from multiple threads. This overload is useful when coordinating access to an observer. Notice reentrant observer callbacks on the same thread are still possible.

Declaration

public static IObserver<T> Synchronize<T>(IObserver<T> observer)

Parameters

Type	Name	Description
IObserver<T>	observer	The observer whose callbacks should be synchronized.

Returns

Type	Description
IObserver<T>	An observer that delivers callbacks to the specified observer in a synchronized manner.

Type Parameters

Name	Description
T	The type of the elements received by the source observer.

Remarks

Because a Monitor is used to perform the synchronization, there's no protection against reentrancy from the same thread. Hence, overlapped observer callbacks are still possible, which is invalid behavior according to the observer grammar. In order to protect against this behavior as well, use the Synchronize<T>(IObserver<T>, Boolean) overload, passing true for the second parameter.

Exceptions

Type	Condition
ArgumentNullException	observer is null.

Synchronize<T>(IObserver<T>, Boolean)

Synchronizes access to the observer such that its callback methods cannot be called concurrently. This overload is useful when coordinating access to an observer. The preventReentrancy parameter configures the type of lock used for synchronization.

Declaration

public static IObserver<T> Synchronize<T>(IObserver<T> observer, bool preventReentrancy)

Parameters

Type	Name	Description
IObserver<T>	observer	The observer whose callbacks should be synchronized.
Boolean	preventReentrancy	If set to true, reentrant observer callbacks will be queued up and get delivered to the observer in a sequential manner.

Returns

Type	Description
IObserver<T>	An observer that delivers callbacks to the specified observer in a synchronized manner.

Type Parameters

Name	Description
T	The type of the elements received by the source observer.

Remarks

When the preventReentrancy parameter is set to false, behavior is identical to the Synchronize<T>(IObserver<T>) overload which uses a Monitor for synchronization. When the preventReentrancy parameter is set to true, an AsyncLock is used to queue up callbacks to the specified observer if a reentrant call is made.

Exceptions

Type	Condition
ArgumentNullException	observer is null.

Synchronize<T>(IObserver<T>, Object)

Synchronizes access to the observer such that its callback methods cannot be called concurrently by multiple threads, using the specified gate object for use by a Monitor-based lock. This overload is useful when coordinating multiple observers that access shared state by synchronizing on a common gate object. Notice reentrant observer callbacks on the same thread are still possible.

Declaration

public static IObserver<T> Synchronize<T>(IObserver<T> observer, object gate)

Parameters

Type	Name	Description
IObserver<T>	observer	The observer whose callbacks should be synchronized.
Object	gate	Gate object to synchronize each observer call on.

Returns

Type	Description
IObserver<T>	An observer that delivers callbacks to the specified observer in a synchronized manner.

Type Parameters

Name	Description
T	The type of the elements received by the source observer.

Remarks

Because a Monitor is used to perform the synchronization, there's no protection against reentrancy from the same thread. Hence, overlapped observer callbacks are still possible, which is invalid behavior according to the observer grammar. In order to protect against this behavior as well, use the Synchronize<T>(IObserver<T>, AsyncLock) overload.

Exceptions

Type	Condition
ArgumentNullException	observer or gate is null.

Synchronize<T>(IObserver<T>, AsyncLock)

Synchronizes access to the observer such that its callback methods cannot be called concurrently, using the specified asynchronous lock to protect against concurrent and reentrant access. This overload is useful when coordinating multiple observers that access shared state by synchronizing on a common asynchronous lock.

Declaration

public static IObserver<T> Synchronize<T>(IObserver<T> observer, AsyncLock asyncLock)

Parameters

Type	Name	Description
IObserver<T>	observer	The observer whose callbacks should be synchronized.
AsyncLock	asyncLock	Gate object to synchronize each observer call on.

Returns

Type	Description
IObserver<T>	An observer that delivers callbacks to the specified observer in a synchronized manner.

Type Parameters

Name	Description
T	The type of the elements received by the source observer.

Exceptions

Type	Condition
ArgumentNullException	observer or asyncLock is null.

ToNotifier<T>(IObserver<T>)

Creates a notification callback from an observer.

Declaration

public static Action<Notification<T>> ToNotifier<T>(this IObserver<T> observer)

Parameters

Type	Name	Description
IObserver<T>	observer	Observer object.

Returns

Type	Description
Action<Notification<T>>	The action that forwards its input notification to the underlying observer.

Type Parameters

Name	Description
T	The type of the elements received by the observer.

Exceptions

Type	Condition
ArgumentNullException	observer is null.

ToObserver<T>(Action<Notification<T>>)

Creates an observer from a notification callback.

Declaration

public static IObserver<T> ToObserver<T>(this Action<Notification<T>> handler)

Parameters

Type	Name	Description
Action<Notification<T>>	handler	Action that handles a notification.

Returns

Type	Description
IObserver<T>	The observer object that invokes the specified handler using a notification corresponding to each message it receives.

Type Parameters

Name	Description
T	The type of the elements received by the observer.

Exceptions

Type	Condition
ArgumentNullException	handler is null.