Predicate(Of T) Delegate
Represents the method that defines a set of criteria and determines whether the specified object meets those criteria.
Assembly: mscorlib (in mscorlib.dll)
'Declaration Public Delegate Function Predicate(Of T) ( _ obj As T _ ) As Boolean 'Usage Dim instance As New Predicate(Of T)(AddressOf HandlerMethod)
Type Parameters
- T
The type of the object to compare.
Parameters
- obj
- Type: T
The object to compare against the criteria defined within the method represented by this delegate.
Return Value
Type: System.Booleantrue if obj meets the criteria defined within the method represented by this delegate; otherwise, false.
This delegate is used by several methods of the Array and List(Of T) classes to search for elements in the collection.
The following code example uses a Predicate(Of T) delegate with the Array.Find(Of T) method to search an array of Point structures. The method the delegate represents, ProductGT10, returns true if the product of the X and Y fields is greater than 100,000. The Find(Of T) method calls the delegate for each element of the array, stopping at the first point that meets the test condition.
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Visual Basic and C# users do not need to create the delegate explicitly, or to specify the type argument of the generic method. The compilers determine the necessary types from the method arguments you supply. |
Imports System Imports System.Drawing Public Class Example Public Shared Sub Main() ' Create an array of five Point structures. Dim points() As Point = { new Point(100, 200), _ new Point(150, 250), new Point(250, 375), _ new Point(275, 395), new Point(295, 450) } ' To find the first Point structure for which X times Y ' is greater than 100000, pass the array and a delegate ' that represents the ProductGT10 method to the Shared ' Find method of the Array class. Dim first As Point = Array.Find(points, _ AddressOf ProductGT10) ' Note that you do not need to create the delegate ' explicitly, or to specify the type parameter of the ' generic method, because the compiler has enough ' context to determine that information for you. ' Display the first structure found. Console.WriteLine("Found: X = {0}, Y = {1}", _ first.X, first.Y) End Sub ' This method implements the test condition for the Find ' method. Private Shared Function ProductGT10(ByVal p As Point) As Boolean If p.X * p.Y > 100000 Then Return True Else Return False End If End Function End Class ' This code example produces the following output: ' 'Found: X = 275, Y = 395
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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.
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