C# check whether value is present in the List<> or not

Question

检查该值是否存在于List然后在c＃中插入该值的有效方法是什么？

Answer 1

You can use Contains method to check whether value is in the list:

if(!valuesList.Contains(value)) 
{
  valuesList.Add(value);
}

Answer 2

Use Contains and Add :

if (!myList.Contains(myValue)) {
    myList.Add(myValue);
}

Answer 3

You're looking for Contains() and Add() , quick example:

if (!theList.Contains(theValue))
{
    theList.Add(theValue);
}

Answer 4

use method bool List.Contains(T) for check, and void List.Add(T) for addition

or create extension:

public static void AddIfNotExist<T>(this List<T> list, T item)
{
    if (list.Contain(item))
    {
        list.Add(item);
    }
}

using list.AddIfNotExist(item)