Observable.FirstOrDefault<TSource> Method (IObservable<TSource>)

Returns the first element of an observable sequence, or a default value if no value is found.

Namespace:  System.Reactive.Linq
Assembly:  System.Reactive (in System.Reactive.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function FirstOrDefault(Of TSource) ( _
    source As IObservable(Of TSource) _
) As TSource

'Usage
Dim source As IObservable(Of TSource)
Dim returnValue As TSource

returnValue = source.FirstOrDefault()

public static TSource FirstOrDefault<TSource>(
    this IObservable<TSource> source
)

[ExtensionAttribute]
public:
generic<typename TSource>
static TSource FirstOrDefault(
    IObservable<TSource>^ source
)

static member FirstOrDefault : 
        source:IObservable<'TSource> -> 'TSource 

JScript does not support generic types and methods.

Type Parameters

• TSource
  The type of source.

Parameters

• source
  Type: System.IObservable<TSource>
  The source observable sequence.

Return Value

Type: TSource
The first element in the observable sequence, or a default value if no value is found.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IObservable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see or .

See Also

Reference

Observable Class

FirstOrDefault Overload

System.Reactive.Linq Namespace