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

Returns the first element of an observable sequence that matches the predicate.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function First(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.First(predicate)

public static TSource First<TSource>(
    this IObservable<TSource> source,
    Func<TSource, bool> predicate
)

[ExtensionAttribute]
public:
generic<typename TSource>
static TSource First(
    IObservable<TSource>^ source, 
    Func<TSource, bool>^ predicate
)

static member First : 
        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 of an observable sequence for which the predicate holds.

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

First Overload

System.Reactive.Linq Namespace