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ContractHandle Class

Provides methods that control the lifetime of an add-in.

Namespace:  System.AddIn.Pipeline
Assembly:  System.AddIn (in System.AddIn.dll)

public class ContractHandle : IDisposable

Because the add-in model provides the ability for add-ins to communicate between application domains and between processes, it cannot rely on the garbage collector to reclaim them. This class provides a reference counting mechanism for the add-in by obtaining a lifetime token to its contract.

When a ContractHandle object is constructed, it calls the AcquireLifetimeToken method on the contract that is passed to the constructor. When the ContractHandle object is disposed or finalized, it calls the RevokeLifetimeToken method on the contract, which removes its hold on the contract.

Adapters implement the contract. The ContractHandle class is designed to be used in a contract-to-view adapter to help pipeline developers manage the lifetime of the contract that is being adapted. Typically, an instance of this class is instantiated during the construction of the adapter class and is stored in an instance field of the adapter. When the adapter class is garbage-collected, the ContractHandle object will also be collected and the ContractHandle object will revoke the lifetime token on the contract.

It is recommended that your view-to-contract adapters inherit from the ContractBase class. You can then use a default implementation for the members of IContract, which means you need to implement only the members of your specific contract.

The following example shows how to set the lifetime token handle in a contract-to-view adapter on the add-in side of a pipeline.

private CalculatorContracts.ICalc2Contract _contract;

private System.AddIn.Pipeline.ContractHandle _handle;

public CalculatorContractToViewHostAdapter(ICalc2Contract contract) {
    _contract = contract;
    _handle = new System.AddIn.Pipeline.ContractHandle(contract);


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5