尝试catch语句C＃中的变量范围问题

Question

I hate to ask this simple of a question on here but I've researched this for a while and to no avail. And it's significantly limiting my application.

Why am I getting a red squiggly on the excelWorksheet variable inside the try block (a local or parameter named 'excelWorksheet' cannot be declared in this scope because that name is used in an enclosing local scope). If I delete the null declaration, then all instances of 'excelWorksheet' after the try catch statement turn red. Any help is extremely appreciated.Here's the code:

 Excel.Worksheet excelWorksheet = null;          
        try
        {
            //declare the worksheet variable raw data
            string currentSheet = "Raw Data";
            Excel.Worksheet excelWorksheet = (Excel.Worksheet)ExcelSheets.get_Item(currentSheet);
        }
        catch(Exception r)
        {
            MessageBox.Show("The Raw Data sheet in the report does not exist. " + r);
            return;
        }

Answer 1

a local or parameter named 'excelWorksheet' cannot be declared in this scope because that name is used in an enclosing local scope

You're trying to re-declare the variable. Remove the declaration and simply use the variable that was declared in the enclosing scope:

string currentSheet = "Raw Data";
excelWorksheet = (Excel.Worksheet)ExcelSheets.get_Item(currentSheet);

Answer 2

Could you try the below?.

Excel.Worksheet excelWorksheet = null;          
            try
            {
                //declare the worksheet variable raw data
                string currentSheet = "Raw Data";

//excelWorksheet variable already exists in the scope, so no need to declare it again

                excelWorksheet = (Excel.Worksheet)ExcelSheets.get_Item(currentSheet);
            }
            catch(Exception r)
            {
                MessageBox.Show("The Raw Data sheet in the report does not exist. " + r);
                return;
            }

Answer 3

Excel.Worksheet excelWorksheet = null;          

with the above statement you already declare the excelWorksheet variable. You do not need to declare again. The code below:

Excel.Worksheet excelWorksheet = null;          
            try
            {
                //declare the worksheet variable raw data
                excelWorksheet = ExcelSheets.get_Item("Raw Data") as Excel.Worksheet;
            }
            catch(Exception r)
            {
                MessageBox.Show("The Raw Data sheet in the report does not exist. " + r);
                return;
            }

Use as for casting. Its a good practice.