如何使int数组为Nullable？

Question

我有这段代码：

var contractsID = contracts.Select(x => x.Id);
int?[] contractsIDList = contractsID.ToArray();//for debug

在这一行：

int?[] contractsIDList = contractsID.ToArray();//for debug

我收到此错误：

  

无法将int []类型隐式转换为int

我尝试做的是使contractIDList为Nullable类型。

如何使int数组为Nullable？

Answer 1

应该获取的错误是：

  

无法将int []类型隐式转换为int？[]

因此您需要转换值：

int?[] contractsIDList = contractsId.Cast<int?>().ToArray();//for debug

Answer 2

您的最简单方法是从int?获取Select：

var contractsID = contracts.Select(x => (int?)x.Id);
int?[] contractsIDList = contractsID.ToArray();

Answer 3

Arrays are always reference types - so they're already nullable.

但我想您实际上想从int?[]获得int[]（因为Id不可为空）。您可以使用Array.ConvertAll：

int[] contractsID = contracts.Select(x => x.Id).ToArray();
int?[] contractsIDList = Array.ConvertAll(contractsID, i => (int?)i);

或直接在LINQ查询中投射：

int?[] contractsIDList = contracts.Select(x => (int?) x.Id).ToArray();

Answer 4

使用此

int?[] contractsIDList = contractsID.ConvertAll<int?>((i) => { int? ni = i; return ni; }).ToArray();