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C# predicate

时间: 2025-01-23 11:03:24 浏览: 38

### C# Predicate Usage and Examples In C#, `Predicate<T>` represents a method that takes an object of type T as its parameter and returns a boolean value indicating whether the specified object meets certain criteria[^1]. Predicates are commonly used in methods like `Find`, `FindAll`, among others to filter elements from collections. #### Basic Syntax A predicate delegate is defined using the following signature: ```csharp public delegate bool Predicate<in T>(T obj); ``` Here, `T` specifies the type of the argument passed into the method represented by this delegate. The method must take one parameter of type `T` and return a Boolean value. #### Example Code Demonstrating Predicate Use To illustrate how predicates work within lists, consider the example below where a list of integers gets filtered based on custom conditions provided via predicates: ```csharp using System; using System.Collections.Generic; class Program { static void Main() { List<int> numbers = new List<int>{ 1, 2, 3, 4, 5 }; // Define a simple predicate function. Predicate<int> greaterThanThree = delegate(int i) { return i > 3; }; int firstMatchedNumber = numbers.Find(greaterThanThree); Console.WriteLine($"First number greater than three: {firstMatchedNumber}"); // Using lambda expression instead of anonymous method var evenNumbers = numbers.FindAll(x => x % 2 == 0); foreach(var num in evenNumbers){ Console.WriteLine(num); } } } ``` This code snippet demonstrates defining both traditional delegates and lambda expressions for filtering purposes. It also shows practical application scenarios such as finding all matching items (`FindAll`) versus just locating the first occurrence (`Find`).

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