包含

MSDN：

使用指定的 IEqualityComparer<T> 確定序列是否包含指定的元素

List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };
var result1 = numbers.Contains(4); // true
var result2 = numbers.Contains(8); // false

List<int> secondNumberCollection = new List<int> { 4, 5, 6, 7 };
// Note that can use the Intersect method in this case
var result3 = secondNumberCollection.Where(item => numbers.Contains(item)); // will be true only for 4,5

使用使用者定義的物件：

public class Person
{
   public string Name { get; set; }
}

List<Person> objects = new List<Person>
{
    new Person { Name = "Nikki"},
    new Person { Name = "Gilad"},
    new Person { Name = "Phil"},
    new Person { Name = "John"}
};

//Using the Person's Equals method - override Equals() and GetHashCode() - otherwise it
//will compare by reference and result will be false
var result4 = objects.Contains(new Person { Name = "Phil" }); // true

使用 Enumerable.Contains(value, comparer) 過載：

public class Compare : IEqualityComparer<Person>
{
    public bool Equals(Person x, Person y)
    {
        return x.Name == y.Name;
    }
    public int GetHashCode(Person codeh)
    {
        return codeh.Name.GetHashCode();
    }
}

var result5 = objects.Contains(new Person { Name = "Phil" }, new Compare()); // true

Contains 的一個聰明用法是將多個 if 子句替換為 Contains 呼叫

所以不要這樣做：

if(status == 1 || status == 3 || status == 4)
{
    //Do some business operation
}
else
{
    //Do something else
}

做這個：

if(new int[] {1, 3, 4 }.Contains(status)
{
    //Do some business operaion
}
else 
{
    //Do something else
}