Export (0) Print
Expand All
Expand Minimize
7 out of 25 rated this helpful - Rate this topic

Predicate Generic Delegate

Represents the method that defines a set of criteria and determines whether the specified object meets those criteria.

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

public delegate bool Predicate<T> (
	T obj
)
J# supports the use of generic types and methods, but not the declaration of new ones.
JScript does not support generic types and methods.
Not applicable.

Type Parameters

T

The type of the object to compare.

Parameters

obj

The object to compare against the criteria defined within the method represented by this delegate.

Return Value

true 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 classes to search for elements in the collection.

The following code example uses a Predicate delegate with the Array.Find 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 method calls the delegate for each element of the array, stopping at the first point that meets the test condition.

NoteNote:

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.

using System;
using System.Drawing;

public class Example
{
    public static void Main()
    {
        // Create an array of five Point structures.
        Point[] points = { 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. 
        Point first = Array.Find(points, ProductGT10);

        // Note that you do not need to create the delegate 
        // explicitly, or to specify the type parameter of the 
        // generic method, because the C# 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);
    }

    // This method implements the test condition for the Find
    // method.
    private static bool ProductGT10(Point p)
    {
        if (p.X * p.Y > 100000)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

/* This code example produces the following output:

Found: X = 275, Y = 395
 */

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

.NET Compact Framework

Supported in: 2.0

XNA Framework

Supported in: 1.0
Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback

Community Additions

ADD
Show:
© 2014 Microsoft. All rights reserved.