While Activity in Visual C#

Encoding ECC200 in Visual C# While Activity

The While activity allows you to perform another activity multiple times, as long as a condition is evaluated to True. The While activity can only have one activity within it, so you might need to use composite activities to perform multiple tasks. The process the While activity goes though is first to evaluate the condition. If the condition is True, the activity within the While activity is executed; otherwise, the While activity completes.

Create a new VB Sequential Workflow Console Application called VBWhileSequentialExample. Open the Workflow.vb file and view the code. Add a private integer variable called IntCounter and assign 0 to the variable using the following code: Private IntCounter As Integer = 0 This not only creates the variable, but also initializes it to 0. Next, add a sub called WhileCondition that assigns the value of IntCounter to e.Result, then increments IntCounter: Public Sub WhileCondition(ByVal sender As Object, ByVal e As ConditionalEventArgs) e.Result = IntCounter < 10 IntCounter = IntCounter + 1 End Sub This sub will be the condition for the While activity. The setup of this condition is the same as the condition for an IfElse activity. The preceding code first determines if the local variable IntCounter is less than 10, then also increments the variable by 1. Next, view the Workflow Designer and add a While activity to the workflow. Leave the name the same, but change the Condition property to be CodeCondition, and choose WhileCondition from the second Condition property drop-down box. This sets up the While activity to look at the WhileCondition. Finally, add a Code activity to the While activity. Leave the name the same, but generate handlers. Within the code handler, add a message box that displays the value of the local variable IntCounter: Private Sub codeActivity1_ExecuteCode(ByVal sender As System.Object, ByVal e As System.EventArgs) MsgBox(IntCounter) End Sub Add a breakpoint to the While activity and debug the workflow. You ll see the While activity is entered first, and then the Code activity. Once inside the loop, the Code activity is the only activity being executed. The Code activity displays the counter each time, until the counter is 10. Although the condition states less than 10, the counter is incremented after that test so the condition stops at 9. However, there s another increment after the condition is met, which displays 10 as the final number. The C# code is only slightly different from the VB code. Create a new C# Sequential Workflow Console Application called CWhileSequentialExample. View the code of the Workflow.cs file and add a new int variable called IntCounter that s initialized to 0: private int IntCounter=0; View the designer and drop a While activity onto the designer. Leave the name the same, but change the condition to a CodeCondition called WhileCondition. Remember, in C# if you enter the name of the condition within the properties, the template code is created for you. Add the assignment to e.Result and the increment, as follows:

private void WhileCondition(object sender, ConditionalEventArgs e) { e.Result = IntCounter < 10; IntCounter++; } Add a Code activity and write to the console the value of IntCounter each time the Code activity is executed. Add a breakpoint to the While activity and debug the application. The console shows each increment of the variable until 10.

Create a new VB State Machine Workflow Console Application called VBWhileStateMachineExample. View the code and create a private integer variable called IntCounter and initialize it to 0: Private IntCounter As Integer = 0 Also, add the WhileCondition sub with the same code as the Sequential workflow example: Public Sub WhileCondition(ByVal sender As Object, ByVal e As ConditionalEventArgs) e.Result = IntCounter < 10 IntCounter = IntCounter + 1 End Sub Name the default state CompletedState and set it as the CompletedState. Add a new State activity with a name of FirstState. Add a StateInitialization activity to the FirstState activity. Within the StateInitialization activity, add a While activity with a Condition property pointing to the WhileCondition sub that was created earlier. Within the While activity, add a Code activity and leave the default name. Generate the handlers for the Code activity and add a message box that displays the value of IntCounter: Private Sub codeActivity1_ExecuteCode(ByVal sender As System.Object, ByVal e As System.EventArgs) MsgBox(IntCounter) End Sub Finally, to avoid an issue with the state machine not completing, add another SetState activity after the While activity. This SetState activity should have the CompletedState as its target state. When the While activity is completed, this SetState activity will complete the workflow; otherwise, when the While activity is completed, the state machine would wait and never complete. The FirstState activity should look like Figure 3-6. Add a breakpoint to the FirstState activity and debug the workflow. Each time the While activity is executed, the Code activity is executed. If you try to use a SetState activity within the While activity to set the state to another state that would have the Code activity in it, the Code activity will never be executed. If you want to execute an activity within the While activity of a state machine, that activity needs to be within the While activity. As with the IfElse example, the code for a C# example of the state machine isn t significantly different from an example for a Sequential workflow, so I won t show that code.