microsoft press windows workflow foundation step by step phần 5 pps

142 Part II Working with Activities

2. Click the View Fault Handlers button to activate the fault handlers visual designer. The

View Fault Handlers button is the right button of the three-button group at the lower-left

corner of the designer window. The designer should appear as you see here:

3. Select the FaultHandler activity from the Toolbox, drag it over the workflow designer’s

fault handler surface, and drop it between the blue arrows.

Your designer surface should now look like this:

4. As with other activities, we have some properties to set to make this fault handler fully

operational. The first property we’ll set is the FaultType property. Select the FaultType

Chapter 7 Basic Activity Operations 143

property in Visual Studio’s Properties pane, and click the browse button (the button

with the three dots) to activate the Browse And Select A .NET Type dialog box.

5. With the Browse And Select A .NET Type dialog box active, select the Type tab if it’s not

already selected and then expand the mscorlib tree node. From there, select System (for

the System assembly) and scroll down the resulting list in the right pane until you find

the list item Exception in the Type Name column. Select this by clicking the Exception

line in the right pane’s ListView control. This places the text “System.Exception” in the

Type Name edit control. Click OK to accept System.Exception as the exception type and

dismiss the dialog box. You should find the value System.Exception has been assigned to

the FaultType property.

Note It’s no coincidence that the exception we’re asking this FaultHandler activity

to use is the same as the exception type thrown by the Throw activity we used earlier

in the chapter. They’re a matched set. If you don’t have a corresponding fault handler

for a Throw activity in your workflow, keep in mind that if the exception is thrown at

runtime, the WorkflowTerminated event is where you’ll soon find your workflow

executing. If this isn’t what you want, add the appropriate FaultHandler activity.

144 Part II Working with Activities

Note Although you see the Fault property in the preceding graphic, it’s actually

disabled and therefore cannot be set. Ignore it.

6. So far, we’ve added a FaultHandler activity and we’ve told it what type of exception it will

be handling, but we’ve not actually provided any code to deal with the exception if it’s

thrown. To do that, drag a Code activity from the Toolbox and drop it into the area below

where we dropped the FaultHandler activity itself. This area, identified by the name

faultHandlerActivity1, is like a miniature workflow visual designer. So it readily accepts

the Code activity, and as we’ve done with other instances of the Code activity, assign a

value to its ExecuteCode property. In this case, type in OnException and press Enter.

7. Visual Studio then adds the OnException event handler to Workflow1 and opens the code

editor for editing. To the OnException event handler, add this code:

Console.WriteLine(

"Exception handled within the workflow! The exception was: '{0}'",

WorkflowException != null ? WorkflowException.Message :

"Exception property not set, generic exception thrown");