c# 判断是否为空然后赋值的4种实现方法

class Aj  {    public void DemoNUll()    {      string str = null;      string result = "";         }  }

if (str == null)        result = "";      else        result = str;

if (str != null){  result = str;}

result = str == null ? "" : str;

result = str ?? "";