private void menageNormalClientList()
        {
            BankClient people = new BankClient();
            while (true)
            {
                if (normalBankClientList.Count > 0)
                {
                    people = normalBankClientList[0];
                    foreach (IBankWindow bw in bankWindowList)
                    {
                        if (!((BankWindow)bw).HasBankClient && ((BankWindow)bw).BankType == BankType.普通)
                        {
                            thread = new Thread(bw.DoSomething);
                            thread.Start(people);
                            ((BankWindow)bw).HasBankClient = true;
                            normalBankClientList.Remove(people);
                            break;
                        }
                    }
                }
            }
        }
people会引发空引用异常，我看了很久都不知道原因

空引用异常是个什么异常

NullReferenceException

设个断点，调试一下就可以了。

调试+研究了很多遍了，就是不知道为什么people会为空，设了list.conunt>0的条件了，如果list里没有对象应该不会执行
people = normalBankClientList[0];
就算执行，也应该抛index越界的异常，所以百思不得其解

也许normalBankClientList[0]的值为null  然后这是normalBankClientList.Count也是大于0的  所以  最终 people被设为null。引发了空异常

检查一下你的BankClient内部吧，问题应该和这个有关吧