尝试这个（LINQ方法语法）：

  string [] columnNames = dt.Columns.Cast< DataColumn>（）
 .Select（x => x.ColumnName ）
 .ToArray（）; 
 

或LINQ查询语法：

  string [] columnNames =（from dc in dt.Columns.Cast< DataColumn>（）
 select dc.ColumnName）.ToArray（）; 
 

需要投放，因为列是键入DataColumnCollection，它是一个 IEnumerable ，而不是 IEnumerable< DataColumn> 。其他部分应该是明显的。

I know we can easily do this by a simple loop, but I want to persue this LINQ/Predicate?

string[] columnNames = dt.Columns.?

or

string[] columnNames = from DataColumn dc in dt.Columns select dc.name;

Try this (LINQ method syntax):

string[] columnNames = dt.Columns.Cast<DataColumn>()
                                 .Select(x => x.ColumnName)
                                 .ToArray();  

or in LINQ Query syntax:

string[] columnNames = (from dc in dt.Columns.Cast<DataColumn>()
                        select dc.ColumnName).ToArray();

Cast is required, because Columns is of type DataColumnCollection which is a IEnumerable, not IEnumerable<DataColumn>. The other parts should be obvious.