在为其分配值之前使用的空例外错误'

Question

我的代码中出现了一个null异常错误，我无法理解为什么。

我在'Resources'中添加了一个名为'FilterXpath'的excel文件添加到我的项目中。我的代码如下：

Dim FilterXpath As Microsoft.Office.Interop.Excel.Application
Dim w As Microsoft.Office.Interop.Excel.worksheet
Dim sheet As Worksheet

w = FilterXpath.Workbooks.Open("C:\Users\sridevi\Documents\Visual Studio 2008\Projects\WindowsApplication2\WindowsApplication2\Resources\FilterXpath.xlsx")
''I got null exception here stating that FilterXpath is used before it has been assigned a value.

Answer 1

将它们声明为New实例

Dim FilterXpath As New Microsoft.Office.Interop.Excel.Application 
Dim w As New Microsoft.Office.Interop.Excel.worksheet Dim sheet As Worksheet