Creating Custom Activities

Article
01/09/2007

To create a basic custom activity, you inherit from the Activity class or a derived type. To create a custom composite activity, you inherit from the CompositeActivity class or a derived type.

Note
Creating a custom activity that inherits from a custom activity containing child activities is not supported.

The custom activity class you create defines the properties, events, and execution logic for the custom activity.

Properties

You may use two types of activity properties in your custom activity: meta properties and instance properties. A meta property is immutable at run time, so the property must be set to a literal value at design time. An instance property can be set at design time or the property can be bound to instance data, in which case the actual value is not determined until run time. Instance properties can also be modified directly during workflow execution.

For more information about activity properties, see Using Activity Properties.

Execution Logic

When you create a custom activity, you must explicitly handle the execution logic of your activity through the Execute method. Additional Activity methods may be overridden as required in your activity.

Attributes

Your custom activity can be decorated with various attributes to indicate such things as which activity designer should be loaded, what validator should be used when validating your activity, and so on. The following table lists all the attributes that you can use to decorate your custom activity.

Attribute	Description
ActivityCodeGeneratorAttribute	Indicates which ActivityCodeGenerator-derived class will be used to generate compile-time code for your custom activity.
ActivityValidatorAttribute	Indicates which ActivityValidator-derived class will be used to validate your custom activity.
AlternateFlowActivityAttribute	Indicates that the activity supports an alternative flow.
ContentPropertyAttribute	Indicates that the property name of a particular property in your custom activity will not be serialized.
DefaultEventAttribute	Indicates the default event of your custom activity.
DesignerAttribute	Indicates which ActivityDesigner-derived class will be used to implement design-time services for your custom activity.
DesignerCategoryAttribute	Indicates that the designer for your custom activity belongs to a certain category.
DesignerSerializerAttribute	Indicates which serializer (ActivityMarkupSerializer, ActivityCodeDomSerializer, ActivityTypeCodeDomSerializer, CompositeActivityMarkupSerializer, or a derivative of any one of them) will be used to serialize your custom activity.
PersistOnCloseAttribute	Indicates that the current workflow instance must be persisted when the adorned activity completes its execution.
RuntimeNamePropertyAttribute	Indicates the run-time name for your custom activity.
ToolboxBitmapAttribute	Indicates the icon to use to represent your custom activity in a container, such as a custom workflow designer.
ToolboxItemAttribute	Indicates which ActivityToolboxItem-derived class will be used with your custom activity in a container, such as a custom workflow designer.
ToolboxItemFilterAttribute	Indicates the filter string and filter type to use for your custom activity when it is used in a container, such as a custom workflow designer.

Caution
If your custom activity uses the PersistOnCloseAttribute, the workflow that uses your custom activity must specify a persistence service to use or an exception is thrown when the workflow is started.

Attributes can be "overridden" in the sense that if you decorate your custom activity with attributes used by your base activity, your overridden values are used against your custom activity. For example, you may want to create your own toolbox bitmap for your custom activity, but still use the default serializer and activity validator of your base activity. To do this, you would only have to decorate your custom activity with the ToolboxItemAttribute and set the value accordingly.