vb.net - Why using DirectCast assigning Excel Objects

Question

I am struggeling with understanding the following code

Dim _xlsSheet As Excel.Worksheet = DirectCast(xlworkbook.Worksheets(Name), Excel.Worksheet)

or

xlworkbook = DirectCast(xlApp.ActiveWorkbook, Excel.Workbook)

All examples I work throu concerning Excel.Interop I see the use of DirectCast everywhere. what i dont understand is why we have to use DirectCast here. If I declare dim xlworkbook as excel.workbook have using directcast instead of just assigning the workbook?

Answer 1

该xlworkbook.Worksheets()方法返回一个Excel.Sheets集合。集合（通常）返回 type 的项目Object，因此，它们应该转换为您期望的类型。

至于xlworkbook = DirectCast(xlApp.ActiveWorkbook, Excel.Workbook)，似乎DirectCast不需要，除非 xlApp 是在没有引用 using 的情况下创建的，否则CreateObject("Excel.Application")会创建一个对象。