Goal of this post

This post is a good example of how to programmatically associate a Workflow to a list.
The workflow can be standard or designed with SharePoint Designer or Visual Studio.
As a workflow is using a standard tasks list and a specific workflow history list to run properly, the code will check and use or create them if necessary.
It will also take care of associating the workflow with a list.

Code example

We assume that the variable web is a SPWeb object containing the list we want to associate the workflow with.

1. Declare objects we are going to use

SPList myList = null;                               // List to associate workflow to
string myListName = null;                           // My list name
SPList historyList = null;                          // Workflow history list
SPList taskList = null;                             // Workflow tasks list
string workflowTemplateGuid = null;                 // Workflow template Guid
SPWorkflowTemplate workflowTemplate = null;         // Workflow template
SPWorkflowAssociation workflowAssociation = null;   // Workflow association
string workflowAssocName = null;                    // Workflow association name

2. Init

Be sure to use the internal name of the list. And set the workflow association name, this will appair as workflow name in SharePoint list settings.

myListName = "My list name";
workflowAssocName = "My Workflow";

3. Get Workflow template

If you want to use a custom workflow and know its template GUID, use the GUID string.

workflowTemplateGuid = "BAD855B1-32CE-4bf1-A29E-463678304E1A";
workflowTemplate = web.WorkflowTemplates[new Guid(workflowTemplateGuid)];

Instead you can get the workflow template GUID by using the GetTemplateByName method.

workflowTemplate = web.WorkflowTemplates.GetTemplateByName(
        "Template name",
        System.Globalization.CultureInfo.CurrentCulture);

4. Get or create workflow history and tasks lists.

The history list is dedicated to workflows and it's based on the WorkflowHistory list template. Most of times you'll have to create it.

// Try to get workflow history list
try
{
      historyList = web.Lists["Workflow History"];
}
catch (ArgumentException exc)
{
      // Create workflow history list
      Guid listGuid = web.Lists.Add("Workflow History", "", SPListTemplateType.WorkflowHistory);
      historyList = web.Lists[listGuid];
      historyList.Hidden = true;
      historyList.Update();
}

The tasks list is a common tasks list based on Tasks list template. If you want to create a specific tasks list for the workflow, don't use "Tasks" title for it. In the example we want to use a dedicated tasks list and will name it "Workflow Tasks".

// Try to get workflow tasks list
try
{
      taskList = web.Lists["Workflow Tasks"];
}
catch (ArgumentException exc)
{
      // Create workflow tasks list
      Guid listGuid = web.Lists.Add("Workflow Tasks", "", SPListTemplateType.Tasks);
      taskList = web.Lists[listGuid];
      taskList.Hidden = true;
      taskList.Update();
}

5. Create workflow association, configure it and associate it to the list.

// Allow unsafe updates on web
web.AllowUnsafeUpdates = true;

try
{
        // Create workflow association
        workflowAssociation = SPWorkflowAssociation.CreateListAssociation(
                workflowTemplate,
                workflowAssocName, taskList, historyList);

        // Set workflow parameters 
        workflowAssociation.AllowManual = false;
        workflowAssociation.AutoStartCreate = true;
        workflowAssociation.AutoStartChange = false;

        // Add workflow association to my list
        myList.AddWorkflowAssociation(workflowAssociation);

        // Enable workflow
        workflowAssociation.Enabled = true;
}
finally
{
        web.AllowUnsafeUpdates = false;
}