Formula attribute added to support in rows with dto or dynamic attrib…

src/MiniExcel/Attributes/ExcelColumnAttribute.cs

@@ -21,6 +21,8 @@ public class ExcelColumnAttribute : Attribute
 
         public bool Ignore { get; set; }
 
+        public bool Formula { get; set; } = false;
+
         public int Index
         {
             get => _index;

src/MiniExcel/OpenXml/Constants/WorksheetXml.cs

@@ -52,8 +52,8 @@ internal static string Column(int? colIndex, double? columnWidth)
         internal static string EmptyCell(string cellReference, string styleIndex)
             => $"<x:c r=\"{cellReference}\" s=\"{styleIndex}\"></x:c>";
         //t check avoid format error ![image](https://user-images.githubusercontent.com/12729184/118770190-9eee3480-b8b3-11eb-9f5a-87a439f5e320.png)
-        internal static string Cell(string cellReference, string cellType, string styleIndex, string cellValue, bool preserveSpace = false)
-            => $"<x:c r=\"{cellReference}\"{(cellType == null ? string.Empty : $" t=\"{cellType}\"")} s=\"{styleIndex}\"{(preserveSpace ? " xml:space=\"preserve\"" : string.Empty)}><x:v>{cellValue}</x:v></x:c>";
+        internal static string Cell(string cellReference, string cellType, string styleIndex, string cellValue, bool preserveSpace = false, bool formula = false)
+            => $"<x:c r=\"{cellReference}\"{(cellType == null ? string.Empty : $" t=\"{cellType}\"")} s=\"{styleIndex}\"{(preserveSpace ? " xml:space=\"preserve\"" : string.Empty)}><x:{(formula ? "f" : "v")}>{cellValue}</x:{(formula ? "f" : "v")}></x:c>";
 
         internal static string Autofilter(string dimensionRef)
             => $"<x:autoFilter ref=\"{dimensionRef}\" />";

src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.Async.cs

@@ -462,7 +462,7 @@ private async Task WriteCellAsync(MiniExcelAsyncStreamWriter writer, int rowInde
 
             /*Prefix and suffix blank space will lost after SaveAs #294*/
             var preserveSpace = cellValue != null && (cellValue.StartsWith(" ", StringComparison.Ordinal) || cellValue.EndsWith(" ", StringComparison.Ordinal));
-            await writer.WriteAsync(WorksheetXml.Cell(columnReference, dataType, styleIndex, cellValue, preserveSpace: preserveSpace));
+            await writer.WriteAsync(WorksheetXml.Cell(columnReference, dataType, styleIndex, cellValue, preserveSpace: preserveSpace, formula: p.ExcelFormula));
         }
 
         private async Task GenerateEndXmlAsync(CancellationToken cancellationToken)

src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.DefaultOpenXml.cs

@@ -103,6 +103,7 @@ private ExcelColumnInfo GetColumnInfosFromDynamicConfiguration(string columnName
 
             prop.Nullable = true;
             prop.ExcelIgnore = dynamicColumn.Ignore;
+            prop.ExcelFormula = dynamicColumn.Formula;
             prop.ExcelColumnIndex = dynamicColumn.Index;
             prop.ExcelColumnWidth = dynamicColumn.Width;
             //prop.ExcludeNullableType = item2[key]?.GetType();

src/MiniExcel/OpenXml/ExcelOpenXmlSheetWriter.cs

@@ -582,7 +582,8 @@ private void WriteCell(MiniExcelStreamWriter writer, int rowIndex, int cellIndex
 
             /*Prefix and suffix blank space will lost after SaveAs #294*/
             var preserveSpace = cellValue != null && (cellValue.StartsWith(" ", StringComparison.Ordinal) || cellValue.EndsWith(" ", StringComparison.Ordinal));
-            writer.Write(WorksheetXml.Cell(columnReference, dataType, styleIndex, cellValue, preserveSpace: preserveSpace));
+            var isFormula = columnInfo?.ExcelFormula ?? false;
+            writer.Write(WorksheetXml.Cell(columnReference, dataType, styleIndex, cellValue, preserveSpace: preserveSpace, formula: isFormula));
         }
 
         private static void WriteCell(MiniExcelStreamWriter writer, string cellReference, string columnName)

src/MiniExcel/Utils/CustomPropertyHelper.cs

@@ -24,6 +24,7 @@ internal class ExcelColumnInfo
         public string ExcelIndexName { get; internal set; }
         public bool ExcelIgnore { get; internal set; }
         public int ExcelFormatId { get; internal set; }
+        public bool ExcelFormula { get; internal set; }
     }
 
     internal class ExcellSheetInfo
@@ -206,7 +207,8 @@ private static IEnumerable<ExcelColumnInfo> ConvertToExcelCustomPropertyInfo(Pro
                     ExcelIndexName = p.GetAttribute<ExcelColumnIndexAttribute>()?.ExcelXName ?? excelColumn?.IndexName,
                     ExcelColumnWidth = p.GetAttribute<ExcelColumnWidthAttribute>()?.ExcelColumnWidth ?? excelColumn?.Width,
                     ExcelFormat = excelFormat ?? excelColumn?.Format,
-                    ExcelFormatId = excelColumn?.FormatId ?? -1
+                    ExcelFormatId = excelColumn?.FormatId ?? -1,
+                    ExcelFormula = excelColumn?.Formula ?? false
                 };
             }).Where(_ => _ != null);
         }
@@ -307,6 +309,7 @@ internal static void SetDictionaryColumnInfo(List<ExcelColumnInfo> _props, objec
                         p.ExcelColumnName = dynamicColumn.Name;
                     isIgnore = dynamicColumn.Ignore;
                     p.ExcelColumnWidth = dynamicColumn.Width;
+                    p.ExcelFormula = dynamicColumn.Formula;
                 }
             }
             if (!isIgnore)