SHARED VARIABLES IN MS CRM 2011

Shared Variables in Microsoft Dynamics crm 2011

 

Here is the nice explaination  from Microsoft MSDN Article

The message pipeline model for Microsoft Dynamics CRM defines a parameter collection of custom data values in the execution context that is passed through the pipeline and shared among registered plug-ins, even from different 3rd party developers.

 This collection of data can be used by different plug-ins to communicate information between plug-ins and enable chain processing where data processed by one plug-in can be processed by the next plug-in in the sequence and so on.

This feature is especially useful in pricing engine scenarios where multiple pricing plug-ins pass data between one another to calculate the total price for a sales order or invoice. Another potential use for this feature is to communicate information between a plug-in registered for a pre-event and a plug-in registered for a post-event.

The name of the parameter that is used for passing information between plug-ins is SharedVariables. This is a collection of key\value pairs. At run time, plug-ins can add, read, or modify properties in the SharedVariables collection. This provides a method of information communication among plug-ins.
This sample shows how to use SharedVariables to pass data from a pre-event registered plug-in to a post-event registered plug-in.

C#

 

using System;

// Microsoft Dynamics CRM namespace(s)
using Microsoft.Xrm.Sdk;

namespace Microsoft.Crm.Sdk.Samples
{
    /// <summary>
    /// A plug-in that sends data to another plug-in through the SharedVariables
    /// property of IPluginExecutionContext.
    /// </summary>
    /// <remarks>Register the PreEventPlugin for a pre-operation stage and the
    /// PostEventPlugin plug-in on a post-operation stage.
    /// </remarks>
    public class PreEventPlugin : IPlugin
    {
        public void Execute(IServiceProvider serviceProvider)
        {
            // Obtain the execution context from the service provider.
            Microsoft.Xrm.Sdk.IPluginExecutionContext context = (Microsoft.Xrm.Sdk.IPluginExecutionContext)
                serviceProvider.GetService(typeof(Microsoft.Xrm.Sdk.IPluginExecutionContext));

            // Create or retrieve some data that will be needed by the post event
            // plug-in. You could run a query, create an entity, or perform a calculation.
            //In this sample, the data to be passed to the post plug-in is
            // represented by a GUID.
            Guid contact = new Guid("{74882D5C-381A-4863-A5B9-B8604615C2D0}");

            // Pass the data to the post event plug-in in an execution context shared
            // variable named PrimaryContact.
            context.SharedVariables.Add("PrimaryContact", (Object)contact.ToString());
        }
    }

    public class PostEventPlugin : IPlugin
    {
        public void Execute(IServiceProvider serviceProvider)
        {
            // Obtain the execution context from the service provider.
            Microsoft.Xrm.Sdk.IPluginExecutionContext context = (Microsoft.Xrm.Sdk.IPluginExecutionContext)
                serviceProvider.GetService(typeof(Microsoft.Xrm.Sdk.IPluginExecutionContext));

            // Obtain the contact from the execution context shared variables.
            if (context.SharedVariables.Contains("PrimaryContact"))
            {
                Guid contact =
                    new Guid((string)context.SharedVariables["PrimaryContact"]);

                // Do something with the contact.
            }
        }
    }
}

It is important that any type of data added to the shared variables collection be serializable otherwise the server will not know how to serialize the data and plug-in execution will fail.

For a plug-in registered in stage 20 or 40, to access the shared variables from a stage 10 registered plug-in that executes on create, update, delete, or by a RetrieveExchangeRateRequest, you must access the ParentContext.SharedVariables collection. For all other cases, IPluginExecutionContext.SharedVariables contains the collection.