Share via

IObserver<T>.OnError(Exception) Method


Notifies the observer that the provider has experienced an error condition.

 void OnError(Exception ^ error);
public void OnError (Exception error);
abstract member OnError : Exception -> unit
Public Sub OnError (error As Exception)



An object that provides additional information about the error.


The following example provides an implementation of the OnError method in a latitude/longitude tracking application. The method simply reports that data is currently unavailable; it does not make use of the Exception object passed to it as a parameter. See the Example section of the IObserver<T> topic for the complete example.

public virtual void OnError(Exception e)
   Console.WriteLine("{0}: The location cannot be determined.", this.Name);
member _.OnError(_) =
    printfn $"{name}: The location cannot be determined."
Public Overridable Sub OnError(ByVal e As System.Exception) Implements System.IObserver(Of Location).OnError
   Console.WriteLine("{0}: The location cannot be determined.", Me.Name)
End Sub


Although error is an object that is derived from System.Exception, it does not necessarily represent an exception that is thrown by the provider. It can also represent a routine or expected error condition, such as data that is missing or unavailable. The OnError method should be seen as informational, and the provider should not expect the observer to provide error handling.

Applies to

See also