C# | Check if every List element matches the predicate conditions

List<T>.TrueForAll(Predicate<T>) is used to check whether every element in the List<T> matches the conditions defined by the specified predicate or not. Syntax:

public bool TrueForAll (Predicate<T> match);

Parameter:

match: It is the Predicate<T> delegate which defines the conditions to check against the elements.

Return Value: This method returns true if every element in the List<T> matches the conditions defined by the specified predicate otherwise it returns false. If the list has no elements, the return value is true. Exception: This method will give ArgumentNullException if the match is null. Below programs illustrate the use of List<T>.TrueForAll(Predicate<T>) Method: Example 1:

CSharp

// C# Program to check if every element
// in the List matches the conditions
// defined by the specified predicate
using System;
using System.Collections;
using System.Collections.Generic;

class Geeks {

    // function which checks whether an
    // element is even or not. Or you can
    // say it is the specified condition
    private static bool isEven(int i)
    {
        return ((i % 2) == 0);
    }

    // Main Method
    public static void Main(String[] args)
    {

        // Creating a List<T> of Integers
        List<int> firstlist = new List<int>();

        // Adding elements to List
        for (int i = 0; i <= 10; i+=2) {
            firstlist.Add(i);
        }

        Console.WriteLine("Elements Present in List:\n");

        // Displaying the elements of List
        foreach(int k in firstlist)
        {
            Console.WriteLine(k);
        }

        Console.WriteLine(" ");

        Console.Write("Result: ");

        // Checks if all the elements of firstlist
        // matches the condition defined by predicate
        Console.WriteLine(firstlist.TrueForAll(isEven));
    }
}

Output:

Elements Present in List:

0
2
4
6
8
10
 
Result: True

Example 2:

CSharp

// C# Program to check if every element
//in the List matches the conditions
//defined by the specified predicate
using System;
using System.Collections;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        List<string> lang = new List<string>();

        lang.Add("C# language");
        lang.Add("C++ language");
        lang.Add("Java language");
        lang.Add("Python language");
        lang.Add("Ruby language");

        Console.WriteLine("Elements Present in List:\n");

        foreach(string language in lang)
        {
            Console.WriteLine(language);
        }

        Console.WriteLine(" ");

        Console.Write("TrueForAll(EndsWithLanguage): ");

        // Checks if all the elements of lang
        // matches the condition defined by predicate
        Console.WriteLine(lang.TrueForAll(EndsWithLanguage));
    }

    // Search predicate returns
    // true if a string ends in "language".
    private static bool EndsWithLanguage(String s)
    {
        return s.ToLower().EndsWith("language");
    }
}

Output:

Elements Present in List:

C# language
C++ language
Java language
Python language
Ruby language
 
TrueForAll(EndsWithLanguage): True

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1.trueforall?view=netframework-4.7.2