C# Feature - Partial events

Partial events

Partial events allow one partial type declaration to define an event and another partial declaration to provide the implementation.

Introduced In

This feature was introduced in C# 14 under the broader “more partial members” work. The official Microsoft Learn page for C# 14 is dated November 18, 2025 and states that C# 14 ships with .NET 10 and Visual Studio 2026.

Why This Feature Exists

Partial events are mainly useful in source-generation and framework scenarios where one part of a type is generated and another part is handwritten.

Example

public partial class OrderMonitor
{
  public partial event EventHandler? Changed;
}

public partial class OrderMonitor
{
  private EventHandler? _changed;

  public partial event EventHandler? Changed
  {
    add => _changed += value;
    remove => _changed -= value;
  }
}

Rules

• A partial event needs exactly one defining declaration and one implementing declaration.
• The defining declaration uses field-like event syntax.
• The implementing declaration must provide add and remove accessors.

Common Pitfalls

• This is a specialized feature; it is rarely needed in typical line-of-business application code.
• Keep generator-produced and handwritten event declarations synchronized exactly.

Related Features

• Partial properties
• Partial constructors