INTRODUCTION TO WORKFLOW AND WINDOWS WORKFLOW FOUNDATION in Visual C#.NET

Generation ECC200 in Visual C#.NET INTRODUCTION TO WORKFLOW AND WINDOWS WORKFLOW FOUNDATION

The preceding section showed how to create each of the new types of workflow projects. However, without an understanding of the out-of-the-box activities, you won t be able to create effective workflow projects. This section will describe all the out-of-the-box activities and indicate which chapter within this book to find out more information about this activity. Code activity: The Code activity allows you to add your own VB or C# code to the workflow. This is a simple form of the custom activity. The actual code resides in a code beside file and gets compiled with the workflow. Any code entered here executes synchronously, so the workflow must wait for it to complete. More information about this activity will follow in 2. Compensate activity: This is an error activity, and can only be added to an exception handler activity. You use this activity to undo actions already performed by the workflow after an error has occurred. This is the equivalent of rolling back a transaction. For more information about the Compensate activity, read 7. Conditional Activity Group: This is a conditional activity that executes other activities based on a condition that applies to the Conditional Activity Group (CAG) or to the activity that s linked to the CAG. Use this grouping of activities to execute a set of activities based on criteria specified for each activity in the group, until some condition is met for the group as a whole. This would allow a group of activities to be executed in parallel, because they each have their own criteria for defining when the activity is complete. You can use a WhenCondition on an activity within the group and an UntilCondition on the group as a whole. All activities continue to execute, if a WhenCondition is provided for the activities, unless the UntilCondition on the group is met. When the UntilCondition on the group is satisfied, the entire group will stop executing. For more information about the CAG, refer to 3. Delay activity: This is a flow activity that allows you to build interval-based pauses into your workflow. With this activity, you can set a duration so that the workflow will pause before continuing to execute. For more information about the Delay activity, refer to 4.

EventDriven activity: This is a flow activity that contains other activities that are to be executed when an event occurs. The event is subscribed to by child activities, such as the Delay activity, which wait for external events to happen. For more information about the EventDriven activity, refer to 4. Fault Handler activity: This is an error handling activity. The Fault Handler activity performs much like the Catch block in code. A workflow can have many of these activities to handle the various types of exceptions that could occur within the workflow. The Fault Handler activity can contain other activities that are fired when an exception is encountered, including a Compensate activity. For more information about the Fault Handler activity, refer to 7. IfElse activity: This is a conditional activity. Use the IfElse activity to execute a branch of activities based on a condition. The first branch must have a condition, but the last branch doesn t require a condition (this is the else part of the activity). The execution is the same as an If Else statement: the first successful branch execution ends the execution of the activity. For more information about the IfElse activity, refer to 3. Invoke Web Service activity: This activity invokes a Web service using a proxy class, and can pass and receive parameters. When invoking a Web service with this activity, you specify a method of the Web service to invoke. For more information about the Invoke Web Service activity, refer to 6. Listen activity: This activity is a composite activity (made up of a minimum of two activities). Each activity that makes up the Listen activity must be an EventDriven activity. The first event raised by an EventDriven activity is executed, and the other EventDriven activity or activities within the Listen activity isn t executed. You can t use a Listen activity in a State Machine workflow. For more information about the Listen activity, refer to 7. Parallel activity: This activity is a composite activity, made up of two or more Sequence activities. The Parallel activity allows the execution of more than one activity at the same time. The activity isn t complete until all Sequence activities that make up the Parallel activity have completed. You need to be careful with the Parallel activity, as more than one Sequence activity within the Parallel activity might attempt to access the same data and could cause conflicts. For more information about the Parallel activity, refer to 4. Policy activity: You can use the Policy activity to represent a collection of rules. A rule has a condition and action or actions that should be taken when that condition is met. The Policy activity allows you to set up a rules-based workflow that can have many conditions, instead of using a series of IfElse activities. For more information about the Policy activity, refer to 5. Replicator activity: The Replicator activity is a conditional activity that s similar to the For Each statement. The Replicator activity creates a number of instances of a single activity while running. All instances must complete before the Replicator activity can complete. For more information about the Replicator activity, refer to 5.