Treat tabs and line breaks as blanks when exporting strings

src/MiniExcel.OpenXml/Constants/ExcelXml.cs

@@ -78,7 +78,7 @@ internal static string SharedStrings(Dictionary<string, int> sharedStrings)
         {
             sb.Append("<x:si><x:t");
 
-            if (text.StartsWith(" ") || text.EndsWith(" "))
+            if (XmlHelper.HasLeadingOrTrailingWhiteSpace(text))
                 sb.Append(" xml:space=\"preserve\"");
 
             sb.Append($">{XmlHelper.EncodeXml(text)}</x:t></x:si>");

src/MiniExcel.OpenXml/Helpers/XmlHelper.cs

@@ -42,6 +42,12 @@ internal static partial class XmlHelper
         return XmlConvert.DecodeName(decodeStr);
     }
 
+    /// <summary>
+    /// Excel drops leading and trailing blanks (spaces, tabs, line breaks) from a &lt;t&gt; without xml:space="preserve".
+    /// </summary>
+    public static bool HasLeadingOrTrailingWhiteSpace(string? text)
+        => text is { Length: > 0 } && (char.IsWhiteSpace(text[0]) || char.IsWhiteSpace(text[text.Length - 1]));
+
     public static string MinifyXml(string xml) => xml
         .Replace("\r", "")
         .Replace("\n", "")

src/MiniExcel.OpenXml/Writer/OpenXmlWriter.cs

@@ -482,7 +482,7 @@ private async Task WriteCellAsync(MiniExcelStreamWriter writer, int rowIndex, in
         }
 
         /*Prefix and suffix blank space will lost after SaveAs #294*/
-        var preserveSpace = cellValue.StartsWith(" ") || cellValue.EndsWith(" ");
+        var preserveSpace = XmlHelper.HasLeadingOrTrailingWhiteSpace(cellValue);
         await writer.WriteAsync(WorksheetXml.Cell(columnReference, dataType, styleIndex, cellValue, preserveSpace: preserveSpace, columnType: columnType), cancellationToken).ConfigureAwait(false);
     }
 

tests/MiniExcel.OpenXml.Tests/Issues/MiniExcelGithubIssuesTests.cs

@@ -1538,6 +1538,25 @@ public void TestIssue294()
         }
     }
 
+    /// A leading or trailing tab or line break is a blank too, inline and shared - https://github.com/mini-software/MiniExcel/issues/294
+    [Theory]
+    [InlineData("\tJack", StringStorageMode.Inline, true)]
+    [InlineData("Jack\n", StringStorageMode.Inline, true)]
+    [InlineData("Ja\tck", StringStorageMode.Inline, false)]
+    [InlineData("\tJack", StringStorageMode.Shared, true)]
+    [InlineData("Jack\n", StringStorageMode.Shared, true)]
+    [InlineData("Ja\tck", StringStorageMode.Shared, false)]
+    public void TestIssue294WhiteSpace(string name, StringStorageMode mode, bool preserved)
+    {
+        using var path = AutoDeletingPath.Create();
+        var value = new[] { new { Name = name } };
+        _excelExporter.Export(path.ToString(), value, configuration: new OpenXmlConfiguration { StringStorageMode = mode });
+
+        var part = mode == StringStorageMode.Shared ? "xl/sharedStrings.xml" : "xl/worksheets/sheet1.xml";
+        var xml = SheetHelper.GetZipFileContent(path.ToString(), part);
+        Assert.Contains(preserved ? $"<x:t xml:space=\"preserve\">{name}</x:t>" : $"<x:t>{name}</x:t>", xml);
+    }
+
     /// Prefix and suffix blank space are hidden by Excel after FillTemplate - https://github.com/mini-software/MiniExcel/issues/295
     [Fact]
     public void TestIssue295()