Collection Activities in WF

This topic applies to Windows Workflow Foundation 4 (WF4).

Collection activities are used to work with collection objects in a workflow. .NET Framework version 4 has system-provided activities for adding and removing items from a collection, testing for the existence of an item in a collection, and clearing a collection. ExistsInCollection and RemoveFromCollection have an OutArgument of type Boolean, which indicates the result.

Note:
If a collection activity is executed before setting the underlying collection object, an InvalidOperationException is thrown and the activity faults.

Collection activities

Using collection activities

The following code example demonstrates how to interact with a collection declared as a workflow variable. The collection used is a List of String objects named fruitList.

Variable<ICollection<string>> fruitList = new Variable<ICollection<string>>
{
    Default = new VisualBasicValue<ICollection<string>>("New List(Of String) From {\"Apple\", \"Orange\"}"),
    Name = "FruitList"
};

Variable<bool> result = new Variable<bool>
{
    Name = "Result"
};

Activity wf = new Sequence
{
    Variables = { fruitList, result },

    Activities = 
    {
        new If
        {
            Condition = new ExistsInCollection<string>
            {
                Collection = fruitList,
                Item = "Pear"
            },
            Then = new AddToCollection<string>
            {
                Collection = fruitList,
                Item = "Pear"
            },
            Else = new RemoveFromCollection<string>
            {
                Collection = fruitList,
                Item = "Apple"
            }
        },

        new RemoveFromCollection<string>
        {
            Collection = fruitList,
            Item = "Apple",
            Result = result
        },
        new If
        {
            Condition = result,
            Then = new ClearCollection<string>
            {
                Collection = fruitList,
            }
        }
    }
};

<Sequence
   xmlns="https://schemas.microsoft.com/netfx/2009/xaml/activities"
   xmlns:scg="clr-namespace:System.Collections.Generic;assembly=mscorlib"
   xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml">
  <Sequence.Variables>
    <x:Reference>__ReferenceID0</x:Reference>
    <x:Reference>__ReferenceID1</x:Reference>
  </Sequence.Variables>
  <If>
    <If.Condition>
      <InArgument
         x:TypeArguments="x:Boolean">
        <ExistsInCollection
           x:TypeArguments="x:String"
           Item="Pear">
          <ExistsInCollection.Result>
            <OutArgument
               x:TypeArguments="x:Boolean" />
          </ExistsInCollection.Result>
          <InArgument
             x:TypeArguments="scg:ICollection(x:String)">
            <VariableValue
               x:TypeArguments="scg:ICollection(x:String)">
              <VariableValue.Result>
                <OutArgument
                   x:TypeArguments="scg:ICollection(x:String)" />
              </VariableValue.Result>
              <VariableValue.Variable>
                <Variable
                   x:TypeArguments="scg:ICollection(x:String)"
                   x:Name="__ReferenceID0"
                   Default="[New List(Of String) From {&quot;Apple&quot;, &quot;Orange&quot;}]"
                   Name="FruitList" />
              </VariableValue.Variable>
            </VariableValue>
          </InArgument>
        </ExistsInCollection>
      </InArgument>
    </If.Condition>
    <If.Then>
      <AddToCollection
         x:TypeArguments="x:String"
         Item="Pear">
        <InArgument
           x:TypeArguments="scg:ICollection(x:String)">
          <VariableValue
             x:TypeArguments="scg:ICollection(x:String)"
             Variable="{x:Reference __ReferenceID0}">
            <VariableValue.Result>
              <OutArgument
                 x:TypeArguments="scg:ICollection(x:String)" />
            </VariableValue.Result>
          </VariableValue>
        </InArgument>
      </AddToCollection>
    </If.Then>
    <If.Else>
      <RemoveFromCollection
         x:TypeArguments="x:String"
         Item="Apple"
         Result="{x:Null}">
        <InArgument
           x:TypeArguments="scg:ICollection(x:String)">
          <VariableValue
             x:TypeArguments="scg:ICollection(x:String)"
             Variable="{x:Reference __ReferenceID0}">
            <VariableValue.Result>
              <OutArgument
                 x:TypeArguments="scg:ICollection(x:String)" />
            </VariableValue.Result>
          </VariableValue>
        </InArgument>
      </RemoveFromCollection>
    </If.Else>
  </If>
  <RemoveFromCollection
     x:TypeArguments="x:String"
     Item="Apple">
    <RemoveFromCollection.Result>
      <OutArgument
         x:TypeArguments="x:Boolean">
        <VariableReference
           x:TypeArguments="x:Boolean">
          <VariableReference.Result>
            <OutArgument
               x:TypeArguments="Location(x:Boolean)" />
          </VariableReference.Result>
          <VariableReference.Variable>
            <Variable
               x:TypeArguments="x:Boolean"
               x:Name="__ReferenceID1"
               Name="Result" />
          </VariableReference.Variable>
        </VariableReference>
      </OutArgument>
    </RemoveFromCollection.Result>
    <InArgument
       x:TypeArguments="scg:ICollection(x:String)">
      <VariableValue
         x:TypeArguments="scg:ICollection(x:String)"
         Variable="{x:Reference __ReferenceID0}">
        <VariableValue.Result>
          <OutArgument
             x:TypeArguments="scg:ICollection(x:String)" />
        </VariableValue.Result>
      </VariableValue>
    </InArgument>
  </RemoveFromCollection>
  <If>
    <If.Condition>
      <InArgument
         x:TypeArguments="x:Boolean">
        <VariableValue
           x:TypeArguments="x:Boolean"
           Variable="{x:Reference __ReferenceID1}">
          <VariableValue.Result>
            <OutArgument
               x:TypeArguments="x:Boolean" />
          </VariableValue.Result>
        </VariableValue>
      </InArgument>
    </If.Condition>
    <If.Then>
      <ClearCollection
         x:TypeArguments="x:String">
        <InArgument
           x:TypeArguments="scg:ICollection(x:String)">
          <VariableValue
             x:TypeArguments="scg:ICollection(x:String)"
             Variable="{x:Reference __ReferenceID0}">
            <VariableValue.Result>
              <OutArgument
                 x:TypeArguments="scg:ICollection(x:String)" />
            </VariableValue.Result>
          </VariableValue>
        </InArgument>
      </ClearCollection>
    </If.Then>
  </If>
</Sequence>

See Also

Tasks

Using Collection Activities

Concepts

Authoring Workflows, Activities, and Expressions Using Imperative Code