Delegate.Combine Method (Delegate, Delegate)
Concatenates the invocation lists of two delegates.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Parameters
- a
- Type: System.Delegate
The delegate whose invocation list comes first.
- b
- Type: System.Delegate
The delegate whose invocation list comes last.
Return Value
Type: System.DelegateA new delegate with an invocation list that concatenates the invocation lists of a and b in that order. Returns a if b is null, returns b if a is a null reference, and returns a null reference if both a and b are null references.
| Exception | Condition |
|---|---|
| ArgumentException | Both a and b are not null, and a and b are not instances of the same delegate type. |
The invocation list can contain duplicate entries; that is, entries that refer to the same method on the same object.
 Note |
|---|
Generic delegates that are assignment-compatible because of variance are not necessarily combinable. To be combinable, the types must match exactly. For example, suppose that a class named Derived is derived from a class named Base. A delegate of type Action<Base> (Action(Of Base) in Visual Basic) can be assigned to a variable of type Action<Derived>, as explained in Covariance and Contravariance in Generics, but the two delegates cannot be combined because the types do not match exactly. |
Combine is useful for creating event handlers that call multiple methods each time an event occurs.
- ReflectionPermission
when invoked late-bound through mechanisms such as Type.InvokeMember. Associated enumeration: ReflectionPermissionFlag.MemberAccess
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
