How to Read Excel Files in C# Without Interop: Complete Developer Guide

using IronXL;
using System;

// Get worksheet by name
WorkSheet workSheet = workBook.GetWorkSheet("GDPByCountry");

Console.WriteLine("Worksheet 'GDPByCountry' not found");
// List available worksheets
foreach (var sheet in workBook.WorkSheets)
{
    Console.WriteLine($"Available: {sheet.Name}");
}

Imports IronXL
Imports System

' Get worksheet by name
Dim workSheet As WorkSheet = workBook.GetWorkSheet("GDPByCountry")

Console.WriteLine("Worksheet 'GDPByCountry' not found")
' List available worksheets
For Each sheet In workBook.WorkSheets
    Console.WriteLine($"Available: {sheet.Name}")
Next

using IronXL;

// Create new XLSX workbook (recommended format)
WorkBook workBook = WorkBook.Create(ExcelFileFormat.XLSX);

// Set workbook metadata
workBook.Metadata.Author = "Your Application";
workBook.Metadata.Comments = "Generated by IronXL";

// Create new XLS workbook for legacy support
WorkBook legacyWorkBook = WorkBook.Create(ExcelFileFormat.XLS);

// Save the workbook
workBook.SaveAs("NewDocument.xlsx");

Imports IronXL

' Create new XLSX workbook (recommended format)
Private workBook As WorkBook = WorkBook.Create(ExcelFileFormat.XLSX)

' Set workbook metadata
workBook.Metadata.Author = "Your Application"
workBook.Metadata.Comments = "Generated by IronXL"

' Create new XLS workbook for legacy support
Dim legacyWorkBook As WorkBook = WorkBook.Create(ExcelFileFormat.XLS)

' Save the workbook
workBook.SaveAs("NewDocument.xlsx")

using IronXL;

// Create multiple worksheets with descriptive names
WorkSheet summarySheet = workBook.CreateWorkSheet("Summary");
WorkSheet dataSheet = workBook.CreateWorkSheet("RawData");
WorkSheet chartSheet = workBook.CreateWorkSheet("Charts");

// Set the active worksheet
workBook.SetActiveTab(0); // Makes "Summary" the active sheet

// Access default worksheet (first sheet)
WorkSheet defaultSheet = workBook.DefaultWorkSheet;

Imports IronXL

' Create multiple worksheets with descriptive names
Dim summarySheet As WorkSheet = workBook.CreateWorkSheet("Summary")
Dim dataSheet As WorkSheet = workBook.CreateWorkSheet("RawData")
Dim chartSheet As WorkSheet = workBook.CreateWorkSheet("Charts")

' Set the active worksheet
workBook.SetActiveTab(0) ' Makes "Summary" the active sheet

' Access default worksheet (first sheet)
Dim defaultSheet As WorkSheet = workBook.DefaultWorkSheet

using IronXL;
using Range = IronXL.Range;

// Select range using Excel notation
Range range = workSheet["D2:D101"];

// Alternative: Use Range class for dynamic selection
Range dynamicRange = workSheet.GetRange("D2:D101"); // Row 2_101, Column D

// Perform bulk operations
range.Value = 0; // Set all cells to 0

Imports IronXL

' Select range using Excel notation
Dim range As Range = workSheet("D2:D101")

' Alternative: Use Range class for dynamic selection
Dim dynamicRange As Range = workSheet.GetRange("D2:D101") ' Row 2_101, Column D

' Perform bulk operations
range.Value = 0 ' Set all cells to 0

// Data validation example
public class ValidationResult
{
    public int Row { get; set; }
    public string PhoneError { get; set; }
    public string EmailError { get; set; }
    public string DateError { get; set; }
    public bool IsValid => string.IsNullOrEmpty(PhoneError) && 
                           string.IsNullOrEmpty(EmailError) && 
                           string.IsNullOrEmpty(DateError);
}

// Validate data in rows 2-101
var results = new List<ValidationResult>();

for (int row = 2; row <= 101; row++)
{
    var result = new ValidationResult { Row = row };

    // Get row data efficiently
    var phoneCell = workSheet[$"B{row}"];
    var emailCell = workSheet[$"D{row}"];
    var dateCell = workSheet[$"E{row}"];

    // Validate phone number
    if (!IsValidPhoneNumber(phoneCell.StringValue))
        result.PhoneError = "Invalid phone format";

    // Validate email
    if (!IsValidEmail(emailCell.StringValue))
        result.EmailError = "Invalid email format";

    // Validate date
    if (!dateCell.IsDateTime)
        result.DateError = "Invalid date format";

    results.Add(result);
}

// Helper methods
bool IsValidPhoneNumber(string phone) => 
    System.Text.RegularExpressions.Regex.IsMatch(phone, @"^\d{3}-\d{3}-\d{4}$");

bool IsValidEmail(string email) => 
    email.Contains("@") && email.Contains(".");

' Data validation example
Public Class ValidationResult
	Public Property Row() As Integer
	Public Property PhoneError() As String
	Public Property EmailError() As String
	Public Property DateError() As String
	Public ReadOnly Property IsValid() As Boolean
		Get
			Return String.IsNullOrEmpty(PhoneError) AndAlso String.IsNullOrEmpty(EmailError) AndAlso String.IsNullOrEmpty(DateError)
		End Get
	End Property
End Class

' Validate data in rows 2-101
Private results = New List(Of ValidationResult)()

For row As Integer = 2 To 101
	Dim result = New ValidationResult With {.Row = row}

	' Get row data efficiently
	Dim phoneCell = workSheet($"B{row}")
	Dim emailCell = workSheet($"D{row}")
	Dim dateCell = workSheet($"E{row}")

	' Validate phone number
	If Not IsValidPhoneNumber(phoneCell.StringValue) Then
		result.PhoneError = "Invalid phone format"
	End If

	' Validate email
	If Not IsValidEmail(emailCell.StringValue) Then
		result.EmailError = "Invalid email format"
	End If

	' Validate date
	If Not dateCell.IsDateTime Then
		result.DateError = "Invalid date format"
	End If

	results.Add(result)
Next row

' Helper methods
'INSTANT VB TODO TASK: Local functions are not converted by Instant VB:
'bool IsValidPhoneNumber(string phone)
'{
'	Return System.Text.RegularExpressions.Regex.IsMatch(phone, "^\d{3}-\d{3}-\d{4}$");
'}

'INSTANT VB TODO TASK: Local functions are not converted by Instant VB:
'bool IsValidEmail(string email)
'{
'	Return email.Contains("@") && email.Contains(".");
'}

using IronXL;

// Add formulas to calculate percentages
int lastRow = 50;
for (int row = 2; row < lastRow; row++)
{
    // Calculate percentage: current value / total
    workSheet[$"C{row}"].Formula = $"=B{row}/B{lastRow}";
    // Format as percentage
    workSheet[$"C{row}"].FormatString = "0.00%";
}
// Add summary formulas
workSheet["B52"].Formula = "=SUM(B2:B50)";      // Sum
workSheet["B53"].Formula = "=AVERAGE(B2:B50)";   // Average
workSheet["B54"].Formula = "=MAX(B2:B50)";       // Maximum
workSheet["B55"].Formula = "=MIN(B2:B50)";       // Minimum
                                                 // Force formula evaluation
workBook.EvaluateAll();

Imports IronXL

' Add formulas to calculate percentages
Dim lastRow As Integer = 50
For row As Integer = 2 To lastRow - 1
    ' Calculate percentage: current value / total
    workSheet($"C{row}").Formula = $"=B{row}/B{lastRow}"
    ' Format as percentage
    workSheet($"C{row}").FormatString = "0.00%"
Next
' Add summary formulas
workSheet("B52").Formula = "=SUM(B2:B50)"      ' Sum
workSheet("B53").Formula = "=AVERAGE(B2:B50)"  ' Average
workSheet("B54").Formula = "=MAX(B2:B50)"      ' Maximum
workSheet("B55").Formula = "=MIN(B2:B50)"      ' Minimum
' Force formula evaluation
workBook.EvaluateAll()

using System.Text.RegularExpressions;
using IronXL;

// Validation implementation
for (int i = 2; i <= 101; i++)
{
    var result = new PersonValidationResult { Row = i };
    results.Add(result);
    
    // Get cells for current person
    var cells = workSheet[$"A{i}:E{i}"].ToList();
    
    // Validate phone (column B)
    string phone = cells[1].StringValue;
    if (!Regex.IsMatch(phone, @"^\+?1?\d{10,14}$"))
    {
        result.PhoneNumberErrorMessage = "Invalid phone format";
    }
    
    // Validate email (column D)
    string email = cells[3].StringValue;
    if (!Regex.IsMatch(email, @"^[^@\s]+@[^@\s]+\.[^@\s]+$"))
    {
        result.EmailErrorMessage = "Invalid email address";
    }
    
    // Validate date (column E)
    if (!cells[4].IsDateTime)
    {
        result.DateErrorMessage = "Invalid date format";
    }
}

Imports System.Text.RegularExpressions
Imports IronXL

' Validation implementation
For i As Integer = 2 To 101
    Dim result As New PersonValidationResult With {.Row = i}
    results.Add(result)
    
    ' Get cells for current person
    Dim cells = workSheet($"A{i}:E{i}").ToList()
    
    ' Validate phone (column B)
    Dim phone As String = cells(1).StringValue
    If Not Regex.IsMatch(phone, "^\+?1?\d{10,14}$") Then
        result.PhoneNumberErrorMessage = "Invalid phone format"
    End If
    
    ' Validate email (column D)
    Dim email As String = cells(3).StringValue
    If Not Regex.IsMatch(email, "^[^@\s]+@[^@\s]+\.[^@\s]+$") Then
        result.EmailErrorMessage = "Invalid email address"
    End If
    
    ' Validate date (column E)
    If Not cells(4).IsDateTime Then
        result.DateErrorMessage = "Invalid date format"
    End If
Next i

// Create results worksheet
var resultsSheet = workBook.CreateWorkSheet("ValidationResults");

// Add headers
resultsSheet["A1"].Value = "Row";
resultsSheet["B1"].Value = "Valid";
resultsSheet["C1"].Value = "Phone Error";
resultsSheet["D1"].Value = "Email Error";
resultsSheet["E1"].Value = "Date Error";

// Style headers
resultsSheet["A1:E1"].Style.Font.Bold = true;
resultsSheet["A1:E1"].Style.SetBackgroundColor("#4472C4");
resultsSheet["A1:E1"].Style.Font.Color = "#FFFFFF";

// Output validation results
for (int i = 0; i < results.Count; i++)
{
    var result = results[i];
    int outputRow = i + 2;
    
    resultsSheet[$"A{outputRow}"].Value = result.Row;
    resultsSheet[$"B{outputRow}"].Value = result.IsValid ? "Yes" : "No";
    resultsSheet[$"C{outputRow}"].Value = result.PhoneNumberErrorMessage ?? "";
    resultsSheet[$"D{outputRow}"].Value = result.EmailErrorMessage ?? "";
    resultsSheet[$"E{outputRow}"].Value = result.DateErrorMessage ?? "";
    
    // Highlight invalid rows
    if (!result.IsValid)
    {
        resultsSheet[$"A{outputRow}:E{outputRow}"].Style.SetBackgroundColor("#FFE6E6");
    }
}

// Auto-fit columns
for (int col = 0; col < 5; col++)
{
    resultsSheet.AutoSizeColumn(col);
}

// Save validated workbook
workBook.SaveAs(@"Spreadsheets\PeopleValidated.xlsx");

Imports System

' Create results worksheet
Dim resultsSheet = workBook.CreateWorkSheet("ValidationResults")

' Add headers
resultsSheet("A1").Value = "Row"
resultsSheet("B1").Value = "Valid"
resultsSheet("C1").Value = "Phone Error"
resultsSheet("D1").Value = "Email Error"
resultsSheet("E1").Value = "Date Error"

' Style headers
resultsSheet("A1:E1").Style.Font.Bold = True
resultsSheet("A1:E1").Style.SetBackgroundColor("#4472C4")
resultsSheet("A1:E1").Style.Font.Color = "#FFFFFF"

' Output validation results
For i As Integer = 0 To results.Count - 1
    Dim result = results(i)
    Dim outputRow As Integer = i + 2

    resultsSheet($"A{outputRow}").Value = result.Row
    resultsSheet($"B{outputRow}").Value = If(result.IsValid, "Yes", "No")
    resultsSheet($"C{outputRow}").Value = If(result.PhoneNumberErrorMessage, "")
    resultsSheet($"D{outputRow}").Value = If(result.EmailErrorMessage, "")
    resultsSheet($"E{outputRow}").Value = If(result.DateErrorMessage, "")

    ' Highlight invalid rows
    If Not result.IsValid Then
        resultsSheet($"A{outputRow}:E{outputRow}").Style.SetBackgroundColor("#FFE6E6")
    End If
Next

' Auto-fit columns
For col As Integer = 0 To 4
    resultsSheet.AutoSizeColumn(col)
Next

' Save validated workbook
workBook.SaveAs("Spreadsheets\PeopleValidated.xlsx")

using System;
using System.ComponentModel.DataAnnotations;
using Microsoft.EntityFrameworkCore;
using IronXL;

// Define entity model
public class Country
{
    [Key]
    public Guid Id { get; set; } = Guid.NewGuid();

    [Required]
    [MaxLength(100)]
    public string Name { get; set; }

    [Range(0, double.MaxValue)]
    public decimal GDP { get; set; }

    public DateTime ImportedDate { get; set; } = DateTime.UtcNow;
}

Imports System
Imports System.ComponentModel.DataAnnotations
Imports Microsoft.EntityFrameworkCore
Imports IronXL

' Define entity model
Public Class Country
	<Key>
	Public Property Id() As Guid = Guid.NewGuid()

	<Required>
	<MaxLength(100)>
	Public Property Name() As String

	<Range(0, Double.MaxValue)>
	Public Property GDP() As Decimal

	Public Property ImportedDate() As DateTime = DateTime.UtcNow
End Class

public class CountryContext : DbContext
{
    public DbSet<Country> Countries { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        // Configure SQLite connection
        optionsBuilder.UseSqlite("Data Source=CountryGDP.db");

        // Enable sensitive data logging in development
        #if DEBUG
        optionsBuilder.EnableSensitiveDataLogging();
        #endif
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Configure decimal precision
        modelBuilder.Entity<Country>()
            .Property(c => c.GDP)
            .HasPrecision(18, 2);
    }
}

Public Class CountryContext
	Inherits DbContext

	Public Property Countries() As DbSet(Of Country)

	Protected Overrides Sub OnConfiguring(ByVal optionsBuilder As DbContextOptionsBuilder)
		' Configure SQLite connection
		optionsBuilder.UseSqlite("Data Source=CountryGDP.db")

		' Enable sensitive data logging in development
		#If DEBUG Then
		optionsBuilder.EnableSensitiveDataLogging()
		#End If
	End Sub

	Protected Overrides Sub OnModelCreating(ByVal modelBuilder As ModelBuilder)
		' Configure decimal precision
		modelBuilder.Entity(Of Country)().Property(Function(c) c.GDP).HasPrecision(18, 2)
	End Sub
End Class

using System.Threading.Tasks;
using IronXL;
using Microsoft.EntityFrameworkCore;

public async Task ImportGDPDataAsync()
{
    try
    {
        // Load Excel file
        var workBook = WorkBook.Load(@"Spreadsheets\GDP.xlsx");
        var workSheet = workBook.GetWorkSheet("GDPByCountry");

        using (var context = new CountryContext())
        {
            // Ensure database exists
            await context.Database.EnsureCreatedAsync();

            // Clear existing data (optional)
            await context.Database.ExecuteSqlRawAsync("DELETE FROM Countries");

            // Import data with progress tracking
            int totalRows = 213;
            for (int row = 2; row <= totalRows; row++)
            {
                // Read country data
                var countryName = workSheet[$"A{row}"].StringValue;
                var gdpValue = workSheet[$"B{row}"].DecimalValue;

                // Skip empty rows
                if (string.IsNullOrWhiteSpace(countryName))
                    continue;

                // Create and add entity
                var country = new Country
                {
                    Name = countryName.Trim(),
                    GDP = gdpValue * 1_000_000 // Convert to actual value if in millions
                };

                await context.Countries.AddAsync(country);

                // Save in batches for performance
                if (row % 50 == 0)
                {
                    await context.SaveChangesAsync();
                    Console.WriteLine($"Imported {row - 1} of {totalRows} countries");
                }
            }

            // Save remaining records
            await context.SaveChangesAsync();
            Console.WriteLine($"Successfully imported {await context.Countries.CountAsync()} countries");
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Import failed: {ex.Message}");
        throw;
    }
}

Imports System.Threading.Tasks
Imports IronXL
Imports Microsoft.EntityFrameworkCore

Public Async Function ImportGDPDataAsync() As Task
	Try
		' Load Excel file
		Dim workBook = WorkBook.Load("Spreadsheets\GDP.xlsx")
		Dim workSheet = workBook.GetWorkSheet("GDPByCountry")

		Using context = New CountryContext()
			' Ensure database exists
			Await context.Database.EnsureCreatedAsync()

			' Clear existing data (optional)
			Await context.Database.ExecuteSqlRawAsync("DELETE FROM Countries")

			' Import data with progress tracking
			Dim totalRows As Integer = 213
			Dim row As Integer = 2
			Do While row <= totalRows
				' Read country data
				Dim countryName = workSheet($"A{row}").StringValue
				Dim gdpValue = workSheet($"B{row}").DecimalValue

				' Skip empty rows
				If String.IsNullOrWhiteSpace(countryName) Then
					row += 1
					Continue Do
				End If

				' Create and add entity
				Dim country As New Country With {
					.Name = countryName.Trim(),
					.GDP = gdpValue * 1_000_000
				}

				Await context.Countries.AddAsync(country)

				' Save in batches for performance
				If row Mod 50 = 0 Then
					Await context.SaveChangesAsync()
					Console.WriteLine($"Imported {row - 1} of {totalRows} countries")
				End If
				row += 1
			Loop

			' Save remaining records
			Await context.SaveChangesAsync()
			Console.WriteLine($"Successfully imported {Await context.Countries.CountAsync()} countries")
		End Using
	Catch ex As Exception
		Console.WriteLine($"Import failed: {ex.Message}")
		Throw
	End Try
End Function

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;
using Newtonsoft.Json;
using IronXL;

// Define data model matching API response
public class RestCountry
{
    public string Name { get; set; }
    public long Population { get; set; }
    public string Region { get; set; }
    public string NumericCode { get; set; }
    public List<Language> Languages { get; set; }
}

public class Language
{
    public string Name { get; set; }
    public string NativeName { get; set; }
}

// Fetch and process API data
public async Task ImportCountryDataAsync()
{
    using var httpClient = new HttpClient();

    try
    {
        // Call REST API
        var response = await httpClient.GetStringAsync("https://restcountries.com/v3.1/all");
        var countries = JsonConvert.DeserializeObject<List<RestCountry>>(response);

        // Create new workbook
        var workBook = WorkBook.Create(ExcelFileFormat.XLSX);
        var workSheet = workBook.CreateWorkSheet("Countries");

        // Add headers with styling
        string[] headers = { "Country", "Population", "Region", "Code", "Language 1", "Language 2", "Language 3" };
        for (int col = 0; col < headers.Length; col++)
        {
            var headerCell = workSheet[0, col];
            headerCell.Value = headers[col];
            headerCell.Style.Font.Bold = true;
            headerCell.Style.SetBackgroundColor("#366092");
            headerCell.Style.Font.Color = "#FFFFFF";
        }

        // Import country data
        await ProcessCountryData(countries, workSheet);

        // Save workbook
        workBook.SaveAs("CountriesFromAPI.xlsx");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"API import failed: {ex.Message}");
    }
}

Imports System
Imports System.Collections.Generic
Imports System.Net.Http
Imports System.Threading.Tasks
Imports Newtonsoft.Json
Imports IronXL

' Define data model matching API response
Public Class RestCountry
	Public Property Name() As String
	Public Property Population() As Long
	Public Property Region() As String
	Public Property NumericCode() As String
	Public Property Languages() As List(Of Language)
End Class

Public Class Language
	Public Property Name() As String
	Public Property NativeName() As String
End Class

' Fetch and process API data
Public Async Function ImportCountryDataAsync() As Task
	Dim httpClient As New HttpClient()

	Try
		' Call REST API
		Dim response = Await httpClient.GetStringAsync("https://restcountries.com/v3.1/all")
		Dim countries = JsonConvert.DeserializeObject(Of List(Of RestCountry))(response)

		' Create new workbook
		Dim workBook = WorkBook.Create(ExcelFileFormat.XLSX)
		Dim workSheet = workBook.CreateWorkSheet("Countries")

		' Add headers with styling
		Dim headers() As String = { "Country", "Population", "Region", "Code", "Language 1", "Language 2", "Language 3" }
		For col As Integer = 0 To headers.Length - 1
			Dim headerCell = workSheet(0, col)
			headerCell.Value = headers(col)
			headerCell.Style.Font.Bold = True
			headerCell.Style.SetBackgroundColor("#366092")
			headerCell.Style.Font.Color = "#FFFFFF"
		Next col

		' Import country data
		Await ProcessCountryData(countries, workSheet)

		' Save workbook
		workBook.SaveAs("CountriesFromAPI.xlsx")
	Catch ex As Exception
		Console.WriteLine($"API import failed: {ex.Message}")
	End Try
End Function

private async Task ProcessCountryData(List<RestCountry> countries, WorkSheet workSheet)
{
    for (int i = 0; i < countries.Count; i++)
    {
        var country = countries[i];
        int row = i + 1; // Start from row 1 (after headers)

        // Write basic country data
        workSheet[$"A{row}"].Value = country.Name;
        workSheet[$"B{row}"].Value = country.Population;
        workSheet[$"C{row}"].Value = country.Region;
        workSheet[$"D{row}"].Value = country.NumericCode;

        // Format population with thousands separator
        workSheet[$"B{row}"].FormatString = "#,##0";

        // Add up to 3 languages
        for (int langIndex = 0; langIndex < Math.Min(3, country.Languages?.Count ?? 0); langIndex++)
        {
            var language = country.Languages[langIndex];
            string columnLetter = ((char)('E' + langIndex)).ToString();
            workSheet[$"{columnLetter}{row}"].Value = language.Name;
        }

        // Add conditional formatting for regions
        if (country.Region == "Europe")
        {
            workSheet[$"C{row}"].Style.SetBackgroundColor("#E6F3FF");
        }
        else if (country.Region == "Asia")
        {
            workSheet[$"C{row}"].Style.SetBackgroundColor("#FFF2E6");
        }

        // Show progress every 50 countries
        if (i % 50 == 0)
        {
            Console.WriteLine($"Processed {i} of {countries.Count} countries");
        }
    }

    // Auto-size all columns
    for (int col = 0; col < 7; col++)
    {
        workSheet.AutoSizeColumn(col);
    }
}

Private Async Function ProcessCountryData(ByVal countries As List(Of RestCountry), ByVal workSheet As WorkSheet) As Task
	For i As Integer = 0 To countries.Count - 1
		Dim country = countries(i)
		Dim row As Integer = i + 1 ' Start from row 1 (after headers)

		' Write basic country data
		workSheet($"A{row}").Value = country.Name
		workSheet($"B{row}").Value = country.Population
		workSheet($"C{row}").Value = country.Region
		workSheet($"D{row}").Value = country.NumericCode

		' Format population with thousands separator
		workSheet($"B{row}").FormatString = "#,##0"

		' Add up to 3 languages
		For langIndex As Integer = 0 To Math.Min(3, If(country.Languages?.Count, 0)) - 1
			Dim language = country.Languages(langIndex)
			Dim columnLetter As String = (ChrW(AscW("E"c) + langIndex)).ToString()
			workSheet($"{columnLetter}{row}").Value = language.Name
		Next langIndex

		' Add conditional formatting for regions
		If country.Region = "Europe" Then
			workSheet($"C{row}").Style.SetBackgroundColor("#E6F3FF")
		ElseIf country.Region = "Asia" Then
			workSheet($"C{row}").Style.SetBackgroundColor("#FFF2E6")
		End If

		' Show progress every 50 countries
		If i Mod 50 = 0 Then
			Console.WriteLine($"Processed {i} of {countries.Count} countries")
		End If
	Next i

	' Auto-size all columns
	For col As Integer = 0 To 6
		workSheet.AutoSizeColumn(col)
	Next col
End Function