Converting an object T into a List<T> in C#

I have a stupid yet braincracker issue about casting types. As you can see from the code I have a variable lprod_monthylReport that depending on the ytm value can be a List<Monthly_Report> or simply a Monthly_Report. I need the variable to have the same name in both cases.

var lprod_monthlyReport = new List<Monthly_Report>;

if (ytm == true)
{
   lprod_monthlyReport = _ProductRep.GetSpecificArchiveReport(prod.Prod_ID, lmonth, lyear, item.item_ID);
}
else
   lprod_monthlyReport = 开发者_运维技巧_ProductRep.GetSpecificYTMReport(prod.Prod_ID, item.item_ID);

The problem is that if I declare the variable inside each if (or else) section the compilers gives error because it says that the variable is already declared in this context.

I already tried casting

lprod_monthlyReport = (Monthly_Report) _ProductRep.GetSpecificArchiveReport(prod.Prod_ID, lmonth, lyear, item.Item_ID);

But it does not work. I also tried the as keyword without success.

May you please help me with this one? Thanks

Francesco

This should work: in case you've got a Monthly_Report just add it to the list...

    List<Monthly_Report> lprod_monthlyReport;
    if (ytm == true)
    {
       lprod_monthlyReport  = new List<Monthly_Report>();
       lprod_monthlyReport.add(_ProductRep.GetSpecificArchiveReport(prod.Prod_ID, lmonth, lyear, item.item_ID));
    }
    else{
       lprod_monthlyReport = _ProductRep.GetSpecificYTMReport(prod.Prod_ID, item.item_ID));
    }

The first line of code

var lprod_monthlyReport = new List<Monthly_Report>;

means that the variable is of type List<Monthly_Report> so it cannot contain a single Monthly_Report object.

This code should be refactored to work differently or have that one method return a List<Monthly_Report> with only one Monthly_Report in it.

The important thing about the var keyword is that it doesn't mean "variant". var is used for type inference by the compiler, which means where you declare:

var something = new List<Something>();

...you are declaring something to be of type List<Something>. This means you can't then do:

something = new Something();

... as you've already declared it as something else. var from a usability perspective is syntactic sugar. The compiler (and the Visual Studio intellisense engine) are using type inference to know that something is actually List<Something>.

This is not going to work, alas.

But you could as alternative wrap the single instance into a list if you wanted. Then you only have to make your code deal with a List<Monthly_Report> of either one or more Monthly_Report items.

declare lprod_monthlyReport as an 'object'. There is no is relationship between Monthly_Report and List<Monthly_Report>.

You will have issues when you come to use the 'lprod_monthlyReport' because you won't know what type it is, other than object, the 'is' keyword could help you then.

Consider that and think about restructuring your code.

Try this

List<Monthly_Report> lprod_monthlyReport;

if (ytm == true) 
{
    lprod_monthlyReport = _ProductRep.GetSpecificArchiveReport(prod.Prod_ID, lmonth, lyear, item.item_ID);
} 
else
{ 
   lprod_monthlyReport = new List<Monthly_Report>() 
    {
       _ProductRep.GetSpecificYTMReport(prod.Prod_ID, item.item_ID)
    };
}