C# 生成1-20随机数 不重复

public void GenerateRandomNums()
{
List list = new List();
Random rand = new Random();
int value;
while(true)
{
if (list.Count == 20)
{
Console.WriteLine("U should get the 20 random numbers. ");
break;
}
value = rand.Next(1, 21);
if(!list.Contains(value))
{
list.Add(value);
}
}
foreach (int temp in list)
{
Console.WriteLine("Num:{0}.", temp);
}
}