打开excel文件报错！！！

Question

Excel.Application app=new Excel.ApplicationClass();
if (app == null) 
{
statusBar1.Text = "ERROR: EXCEL couldn't be started!";
return ;
}
app.Visible = true; 
app.UserControl = true;
Excel.WorkbookClass workbook =(Excel.WorkbookClass)   app.Workbooks.Add("c:\\t1.xls");
Excel.WorksheetClass worksheet=(Excel.WorksheetClass)workbook.Sheets.get_Item(0）///这里错误，该怎么改？？？
if(worksheet==null)
{
statusBar1.Text =  "ERROR: worksheet == null";
return;
}
Excel.Range range1=worksheet.get_Range("A1","A5");

Answer 1

Excel.WorkbookClass workbook =(Excel.WorkbookClass)   app.Workbooks.Add("c:\\t1.xls");
Excel.WorksheetClass worksheet=(Excel.WorksheetClass)workbook.Sheets.get_Item(0）
改为：
app.Workbooks.Add("c:\\t1.xls");
Excel.Workbook workbook = app.Workbooks[1];
Excel.Worksheet worksheet=(Excel.Worksheet)workbook.Sheets[1];