调试一些代码并找到??在代码里面。这是什么意思?
答案 0 :(得分:16)
??
是可以为空的类型的null-coalescing operator。
object obj = canBeNull ?? alternative;
// equivalent to:
object obj = canBeNull != null ? canBeNull : alternative;
答案 1 :(得分:5)
http://msdn.microsoft.com/en-us/library/ms173224.aspx请参阅此说明。这是一个运营商
??
运算符定义了将可空类型分配给非可空类型时要返回的默认值。
// ?? operator example.
int x = null;
// y = x, unless x is null, in which case y = -1.
int y = x ?? -1;
// Assign i to return value of method, unless
// return value is null, in which case assign
// default value of int to i.
int i = GetNullableInt() ?? default(int);
string s = GetStringValue();
// ?? also works with reference types.
// Display contents of s, unless s is null,
// in which case display "Unspecified".
Console.WriteLine(s ?? "Unspecified");