一、空值判断效率
string s = "";

1. if(s == ""){}
2. if(s == string.Empty){}
3. if (string.IsNullOrEmpty(s)) {}
4. if(s != null && s.Length ==0) {}
5. if((s+"").Length == 0){}

1,2最慢；3较快；4,5最快
1,2几乎没区别；4,5几乎没区别

二、空值和null判断

1. if (string.IsNullOrEmpty(s)) {}
2. if(s == null || s.Length == 0) {}
3. string.IsNullOrWhiteSpace性能更高

推荐用2,3