如何定义IList <T> 在界面中

Question

I have method readExcelFile() which takes parameter and generic type where generic type is class so the idea is give this method require parameter to read excel file and I get List of object having excel records.

The all is working fine that state above but I also need to define interface

public interface IProcessExcel 
{
    IList<T> ReadExcelFile(string filePath, int readExcelRowFrom, int headerRow);  
}

and in above code I am getting error

 The Type or namespace T could not be found(missing directive or assembly )

implementation code

 public class ProcessExcel<T>: IProcessExcel where T: class
{
    private static Excel.Application xlApp;
    private static Excel.Workbook xlWorkbook;
    private static Excel.Worksheet xlWorkSheet;
    private static Excel.Range xlRange;
    private string GivenFilePath = string.Empty;        
    private IList<string> ExcelFileExtensionList = new string[] { ".xls", ".xlsx", ".xlsm", ".xltx", ".xltm" };
    private T newObject;
    List<T> ExcelRecordList = new List<T>();

    public ProcessExcel()
    {
    }


    public IList<T> ReadExcelFile(string filePath, int readExcelRowFrom, int headerRow) 
    {
        this.FilePath = filePath;
        this.ReadExcelRowFrom = readExcelRowFrom;
        this.HeaderRow = headerRow;
        this.ReferenceClass = typeof(T);
        this.ValidateExcelFile();
         this.ProcessReadExcelFile();

        return ReadExcelFile;
    }

Answer 1

You need to define a generic interface as well

public interface IProcessExcel<T> where T:class
{
    IList<T> ReadExcelFile(string filePath, int readExcelRowFrom, int headerRow);  
}

The compiler doesn't know how to determine the T later.

The class then, will be defined like this:

public class ProcessExcel<T>: IProcessExcel<T> where T: class

Answer 2

You need to implement the generic method correctly in both Interface and in Class Like this :

public interface IProcessExcel { IList<T> ReadExcelFile<T>(string filePath, int readExcelRowFrom, int headerRow);
}

Notice the declaration of 'T' after the Method Name.