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)
Syntax
'Declaration
<ExtensionAttribute> _
Public Shared Function FirstOrDefault(Of TSource) ( _
source As IObservable(Of TSource), _
predicate As Func(Of TSource, Boolean) _
) As TSource
'Usage
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
)
[ExtensionAttribute]
public:
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.
Parameters
- source
Type: System.IObservable<TSource>
The source observable sequence.
- 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 .