Enumerable.TakeWhile(TSource) Method (IEnumerable(TSource), Func(TSource, Int32, Boolean))
Returns elements from a sequence as long as a specified condition is true. The element's index is used in the logic of the predicate function.
Assembly: System.Core (in System.Core.dll)
The type of the elements of source.
- Type: System.Collections.Generic.IEnumerable()
The sequence to return elements from.
Return ValueType: System.Collections.Generic.IEnumerable()
An IEnumerable(T) that contains elements from the input sequence that occur before the element at which the test no longer passes.
Usage NoteIn Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(). When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).
source or predicate is a null reference (Nothing in Visual Basic).
This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.
The method tests each element of source by using predicate and yields the element if the result is true. Enumeration stops when the predicate function returns false for an element or when source contains no more elements.
The first argument of predicate represents the element to test. The second argument represents the zero-based index of the element within source.
The TakeWhile and SkipWhile methods are functional complements. Given a sequence coll and a pure function p, concatenating the results of coll.TakeWhile(p) and coll.SkipWhile(p) yields the same sequence as coll.
In Visual Basic query expression syntax, a Take While clause translates to an invocation of TakeWhile.
Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.