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Observable.FirstOrDefault<TSource> Method (IObservable<TSource>, Func<TSource, Boolean>)

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

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


<ExtensionAttribute> _
Public Shared Function FirstOrDefault(Of TSource) ( _
    source As IObservable(Of TSource), _
    predicate As Func(Of TSource, Boolean) _
) As TSource
Dim source As IObservable(Of TSource)
Dim predicate As Func(Of TSource, Boolean)
Dim returnValue As TSource

returnValue = source.FirstOrDefault(predicate)
public static TSource FirstOrDefault<TSource>(
    this IObservable<TSource> source,
    Func<TSource, bool> predicate
generic<typename TSource>
static TSource FirstOrDefault(
    IObservable<TSource>^ source, 
    Func<TSource, bool>^ predicate
static member FirstOrDefault : 
        source:IObservable<'TSource> * 
        predicate:Func<'TSource, bool> -> 'TSource 
JScript does not support generic types and methods.

Type Parameters

  • TSource
    The type of source.


  • predicate
    Type: System.Func<TSource, Boolean>
    A predicate function to evaluate for elements in the sequence.

Return Value

Type: TSource
The first element in the observable sequence for which the predicate holds, 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


Observable Class

FirstOrDefault Overload

System.Reactive.Linq Namespace