Yuno's Note of Coding

// 判斷字串是不是 null
string value1 = null;
bool result1 = (value1 == null);

// 判斷字串是不是空字串
string value2A = string.Empty;
bool result2A = (value2A == string.Empty);

string value2B = "";
bool result2B = (value2B == string.Empty);

// 判斷字串是不是連續空白
string value3 = "     ";
bool result3 = (value3.Trim() == string.Empty); // Trim() 用來將字串左右的空白刪除, 但不刪除字串中間的空白(ex:"te st")

// 判斷字串是不是null 或空字串
value1 = null;
result1 = string.IsNullOrEmpty(value1);
value2A = string.Empty;
result2A = string.IsNullOrEmpty(value2A);

// 判斷字串是不是null, 空字串,或連續空白字串
value1 = null;
result1 = string.IsNullOrWhiteSpace(value1);
value2A = string.Empty;
result2A = string.IsNullOrWhiteSpace(value2A);
value3 = "   ";
result3 = string.IsNullOrWhiteSpace(value3);

參考資料：

https://docs.microsoft.com/zh-tw/dotnet/api/system.string.isnullorempty

https://docs.microsoft.com/zh-tw/dotnet/api/system.string.isnullorwhitespace