List<'T>.Exists Method (Predicate<'T>)

 

Determines whether the List<'T> contains elements that match the conditions defined by the specified predicate.

Namespace:   System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

member Exists : 
        match:Predicate<'T> -> bool

Parameters

match
Type: System.Predicate<'T>

The Predicate<'T> delegate that defines the conditions of the elements to search for.

Return Value

Type: System.Boolean

true if the List<'T> contains one or more elements that match the conditions defined by the specified predicate; otherwise, false.

Exception Condition
ArgumentNullException

match is null.

The Predicate<'T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of the current List<'T> are individually passed to the Predicate<'T> delegate, and processing is stopped when a match is found.

This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

The following example demonstrates the Contains and Existsmethods on a List<'T> that contains a simple business object that implements Equals.

No code example is currently available or this language may not be supported.

The following example demonstrates the Exists method and several other methods that use the Predicate<'T> generic delegate.

A List<'T> of strings is created, containing 8 dinosaur names, two of which (at positions 1 and 5) end with "saurus". The example also defines a search predicate method named EndsWithSaurus, which accepts a string parameter and returns a Boolean value indicating whether the input string ends in "saurus".

The Find, FindLast, and FindAll methods are used to search the list with the search predicate method, and then the RemoveAll method is used to remove all entries ending with "saurus".

Finally, the Exists method is called. It traverses the list from the beginning, passing each element in turn to the EndsWithSaurus method. The search stops and the method returns true if the EndsWithSaurus method returns true for any element. The Exists method returns false because all such elements have been removed.

System_CAPS_noteNote

In C# and Visual Basic, it is not necessary to create the Predicate<string> delegate (Predicate(Of String) in Visual Basic) explicitly. These languages infer the correct delegate from context and create it automatically.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
Return to top
Show: