C＃无法隐式转换类型&#39;System.Collections.Generic.List <string> &#39;到&#39;System.Windows.Documents.List&#39;

Question

I want to make a method that returns a list. But when I declare the datatype string tot the list it gives me this error:

Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Windows.Documents.List'

at the return statement.

private List StockCheck(List<string> ListStockCheck, string[] StringProducts, int[,] productstock)
{
    for (int product = 0; product < StringProducts.GetLength(0); product++) 
    {               
        for (int dag = 0; dag < this.productStock.GetLength(1); dag++)
        {
            sumP[product] += this.productStock[product, dag];
        }               
        if(sumP[product] >=115 && sumP[product] <= 190)
        {
            ListVoorraadCheck.Add("De voorraad van " + StringProducts[product] + " is goed!");
        }
    }
    return ListStockCheck;
}

It shows the error on the return ListStockCheck; statement.

Does anyone know how to fix this?

Answer 1

Well you actually don't need to return anything at all as far as I can see. List is not used at all in the method and if it is, you are returning a parameter, so you have it already since you have to pass it to the method. As one of the commentator has written it's not necessary in C# to return something, you can write private void MyMethod() , then you don't need a return.

There can be some cases when you want that like Fluent interface, but it does not look like it's what you want here.

If you still want to return it you need to change the return type to be the same as parameter, eg List<string> .

You can use other types like eg IEnumerable<string> , IList<string> , etc. including non-generic IEnumerable and IList . It depends on what you want to achieve which type to return.

Answer 2

List<T> is a generic Type, Using generic type requires parameters. Since your are returning ListStockCheck I am assuming you want to return list of string ie List<string> . Thus your return type should be something like below

   private List<string> StockCheck(List<string> ListStockCheck, string[] StringProducts, int[,] productstock)
   { 
    // Other code
   }