Error List

The Error List window displays errors, warnings, and messages from builds, analyzers, and extensions. Your extension can add custom entries to help users identify and navigate to problems.

Quick Start with Community Toolkit

// Add an error
await VS.MessageBox.ShowErrorAsync("Something went wrong");

// For Error List entries, use TableDataSource (see complete example below)

Using ErrorListProvider

The ErrorListProvider class is the standard way to add items to the Error List:

using Microsoft.VisualStudio.Shell;
using System;

public class MyErrorListManager : IDisposable
{
    private readonly ErrorListProvider _errorListProvider;

    public MyErrorListManager(IServiceProvider serviceProvider)
    {
        _errorListProvider = new ErrorListProvider(serviceProvider)
        {
            ProviderName = "My Extension",
            ProviderGuid = new Guid("YOUR-GUID-HERE")
        };
    }

    public void AddError(string message, string filePath, int line, int column)
    {
        var task = new ErrorTask
        {
            Category = TaskCategory.BuildCompile,
            ErrorCategory = TaskErrorCategory.Error,
            Text = message,
            Document = filePath,
            Line = line - 1,      // Error List uses 0-based line numbers
            Column = column - 1,  // Error List uses 0-based column numbers
            CanDelete = true,
            HierarchyItem = null
        };

        // Enable navigation to the error location
        task.Navigate += (s, e) =>
        {
            task.Line++; // Navigate uses 1-based
            _errorListProvider.Navigate(task, Guid.Empty);
            task.Line--;
        };

        _errorListProvider.Tasks.Add(task);
    }

    public void AddWarning(string message, string filePath, int line, int column)
    {
        var task = new ErrorTask
        {
            Category = TaskCategory.BuildCompile,
            ErrorCategory = TaskErrorCategory.Warning,
            Text = message,
            Document = filePath,
            Line = line - 1,
            Column = column - 1
        };

        task.Navigate += (s, e) => _errorListProvider.Navigate(task, Guid.Empty);
        _errorListProvider.Tasks.Add(task);
    }

    public void AddMessage(string message)
    {
        var task = new ErrorTask
        {
            Category = TaskCategory.BuildCompile,
            ErrorCategory = TaskErrorCategory.Message,
            Text = message
        };

        _errorListProvider.Tasks.Add(task);
    }

    public void Clear()
    {
        _errorListProvider.Tasks.Clear();
    }

    public void Show()
    {
        _errorListProvider.Show();
        _errorListProvider.BringToFront();
    }

    public void Dispose()
    {
        _errorListProvider?.Dispose();
    }
}

ErrorTask Properties

Property	Type	Description
`ErrorCategory`	`TaskErrorCategory`	Error, Warning, or Message
`Category`	`TaskCategory`	BuildCompile, CodeSense, Comments, etc.
`Text`	`string`	The message displayed
`Document`	`string`	Full path to the file
`Line`	`int`	0-based line number
`Column`	`int`	0-based column number
`HelpKeyword`	`string`	F1 help keyword
`CanDelete`	`bool`	Whether user can delete the entry
`Priority`	`TaskPriority`	High, Normal, or Low
`Subcategory`	`string`	Additional categorization

Error Categories

// Errors - Red X icon, blocks build success
task.ErrorCategory = TaskErrorCategory.Error;

// Warnings - Yellow triangle icon
task.ErrorCategory = TaskErrorCategory.Warning;

// Messages - Blue info icon
task.ErrorCategory = TaskErrorCategory.Message;

Task Categories

The TaskCategory determines which filter shows the error:

// Build errors (shown in Build + IntelliSense filter)
task.Category = TaskCategory.BuildCompile;

// IntelliSense errors (shown in IntelliSense filter only)
task.Category = TaskCategory.CodeSense;

// Comment tasks like TODO (shown in Tasks view)
task.Category = TaskCategory.Comments;

// General/other
task.Category = TaskCategory.Misc;

Enable clicking an error to navigate to the source location:

public void AddNavigableError(string message, string filePath, int line, int column)
{
    var task = new ErrorTask
    {
        ErrorCategory = TaskErrorCategory.Error,
        Text = message,
        Document = filePath,
        Line = line - 1,
        Column = column - 1
    };

    // Handle double-click navigation
    task.Navigate += (sender, e) =>
    {
        // Open the document and navigate to line/column
        VsShellUtilities.OpenDocument(
            _serviceProvider,
            filePath,
            Guid.Empty,
            out _,
            out _,
            out var windowFrame);

        windowFrame?.Show();

        // Move to the specific line
        var textView = VsShellUtilities.GetTextView(windowFrame);
        textView?.SetCaretPos(line - 1, column - 1);
    };

    _errorListProvider.Tasks.Add(task);
}

ErrorListProvider.Navigate handles most navigation automatically:

task.Navigate += (s, e) =>
{
    // Navigate uses 1-based line numbers internally
    var originalLine = task.Line;
    task.Line++; // Convert to 1-based
    _errorListProvider.Navigate(task, VSConstants.LOGVIEWID_Code);
    task.Line = originalLine; // Restore
};

Adding Error Codes

Include an error code for documentation lookup:

var task = new ErrorTask
{
    ErrorCategory = TaskErrorCategory.Error,
    Text = "Null reference detected",
    Subcategory = "MY001", // Appears in Code column
    HelpKeyword = "MY001", // F1 help lookup
    Document = filePath,
    Line = line - 1
};

Project-Specific Errors

Associate errors with a specific project:

public async Task AddProjectErrorAsync(string message, Project project, string filePath, int line)
{
    await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync();

    var hierarchy = await project.ToHierarchyItemAsync();

    var task = new ErrorTask
    {
        ErrorCategory = TaskErrorCategory.Error,
        Text = message,
        Document = filePath,
        Line = line - 1,
        HierarchyItem = hierarchy // Associates with project
    };

    _errorListProvider.Tasks.Add(task);
}

Complete Example

A validation service that reports errors to the Error List:

using Microsoft.VisualStudio.Shell;
using Microsoft.VisualStudio.Shell.Interop;
using System;
using System.Collections.Generic;

public class ValidationService : IDisposable
{
    private readonly ErrorListProvider _errorListProvider;
    private readonly IServiceProvider _serviceProvider;

    public ValidationService(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
        _errorListProvider = new ErrorListProvider(serviceProvider)
        {
            ProviderName = "My Validator",
            ProviderGuid = new Guid("12345678-1234-1234-1234-123456789012")
        };
    }

    public void ValidateDocument(string filePath, string content)
    {
        // Clear previous errors for this file
        ClearErrorsForFile(filePath);

        var errors = PerformValidation(content);

        foreach (var error in errors)
        {
            AddError(error, filePath);
        }

        if (errors.Count > 0)
        {
            _errorListProvider.Show();
        }
    }

    private void AddError(ValidationError error, string filePath)
    {
        var task = new ErrorTask
        {
            Category = TaskCategory.CodeSense,
            ErrorCategory = error.Severity,
            Text = error.Message,
            Document = filePath,
            Line = error.Line - 1,
            Column = error.Column - 1,
            Subcategory = error.Code,
            HelpKeyword = error.Code
        };

        task.Navigate += (s, e) =>
        {
            task.Line++;
            _errorListProvider.Navigate(task, VSConstants.LOGVIEWID_Code);
            task.Line--;
        };

        _errorListProvider.Tasks.Add(task);
    }

    public void ClearErrorsForFile(string filePath)
    {
        for (int i = _errorListProvider.Tasks.Count - 1; i >= 0; i--)
        {
            if (_errorListProvider.Tasks[i] is ErrorTask task &&
                string.Equals(task.Document, filePath, StringComparison.OrdinalIgnoreCase))
            {
                _errorListProvider.Tasks.RemoveAt(i);
            }
        }
    }

    public void ClearAll()
    {
        _errorListProvider.Tasks.Clear();
    }

    private List<ValidationError> PerformValidation(string content)
    {
        // Your validation logic here
        return new List<ValidationError>();
    }

    public void Dispose()
    {
        _errorListProvider?.Dispose();
    }
}

public class ValidationError
{
    public string Code { get; set; }
    public string Message { get; set; }
    public int Line { get; set; }
    public int Column { get; set; }
    public TaskErrorCategory Severity { get; set; }
}

Integration with Package

[PackageRegistration(UseManagedResourcesOnly = true, AllowsBackgroundLoading = true)]
[Guid(PackageGuids.MyPackageString)]
public sealed class MyPackage : AsyncPackage
{
    private ValidationService _validationService;

    protected override async Task InitializeAsync(
        CancellationToken cancellationToken,
        IProgress<ServiceProgressData> progress)
    {
        await base.InitializeAsync(cancellationToken, progress);
        await JoinableTaskFactory.SwitchToMainThreadAsync(cancellationToken);

        _validationService = new ValidationService(this);
    }

    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            _validationService?.Dispose();
        }
        base.Dispose(disposing);
    }
}

Best Practices

Clear old errors - Remove stale errors when re-validating a file
Use appropriate categories - BuildCompile for build errors, CodeSense for live analysis
Enable navigation - Users expect to click errors to go to the source
Include error codes - Helps users search for documentation
Don’t flood the list - Too many errors can be overwhelming
Dispose properly - Clean up ErrorListProvider when your extension unloads

Warning

Line and column numbers in ErrorTask are 0-based, but most editors display 1-based numbers. Remember to convert when setting values.

Tip

For Roslyn-based analyzers, use the DiagnosticAnalyzer API instead of ErrorListProvider. Roslyn handles Error List integration automatically.

IVsErrorList Interface

For advanced scenarios, use the IVsErrorList service directly:

var errorList = await VS.Services.GetErrorListAsync();
// or
var errorList = (IVsErrorList)GetService(typeof(SVsErrorList));

// Bring Error List to front
errorList.BringToFront();

// Force refresh
errorList.ForceShowErrors((uint)(__VSERRORCATEGORY.EC_WARNING | __VSERRORCATEGORY.EC_ERROR), out _);

Error List

Quick Start with Community Toolkit

Using ErrorListProvider

ErrorTask Properties

Error Categories

Task Categories

Navigation Support

Simplified Navigation

Adding Error Codes

Project-Specific Errors

Complete Example

Integration with Package

Best Practices

IVsErrorList Interface

See Also