已经为类型参数“Chart”指定了 constraint 子句。必须在单个 where 子句中指定类型参数的所有约束

public abstract class FillWorkBook<TModel, Chart>
    where TModel : struct
    where Chart : new()
    where Chart : CreateExcelBase
{

    public void FillDataToWorkbook(Workbook workbook)
    {
        List<TModel> sheetData = GetData();
        if (sheetData == null)
        {
            sheetData = new List<TModel>();
        }
        DataTable dt = AsConvert.ListToDataTable(sheetData);
        CreateExcelBase chart = new Chart();
        chart.FillData = dt;
        chart.CreateCharts(workbook);

    }

    public abstract List<TModel> GetData();
}

public abstract class FillWorkBook<TModel, Chart>
    where TModel : struct
    where Chart : CreateExcelBase,new()