C# 4 and .NET 4

Custom activities ❘ OC291
With all of these changes in place, you can compile the assembly and then create a new workflow project.
To add the activity to the toolbox, open a workflow and then display the context menu for the toolbox and
click Choose Items.
You can then browse for the assembly containing your activity, and once you
have added it to the toolbox, it will look something like Figure 57-12. The icon is
somewhat less than perfect, but it’s close enough.
You revisit the ActivityToolboxItem in the next section on custom composite activities, because there are
some extra facilities available with that class that are necessary only when adding composite activities to the
design surface.
To recap, you’ve created a custom WriteLineActivity, added validation logic by creating the
WriteLineValidator, created a designer and a theme with the WriteLineDesigner and WriteLineTheme
classes, created a bitmap for the activity, and lastly created the WriteLineToolboxItem class to alter the
display name of the activity.
Custom Composite activities
There are two main types of activity. Activities that derive from Activity can be thought of as callable
functions from the workflow. Activities that derive from CompositeActivity (such as ParallelActivity,
IfElseActivity, and the ListenActivity) are containers for other activities. Their design-time behavior
is considerably different from simple activities in that they present an area on the Designer where child
activities can be dropped.
In this section, you create an activity that you can call the DaysOfWeekActivity. This activity can be used
to execute different parts of a workflow based on the current date. You might, for instance, need to execute
a different path in the workflow for orders that arrive over the weekend than for those that arrive during
the week. In this example, you learn about a number of advanced workflow topics, and by the end of this
section, you should have a good understanding of how to extend the system with your own composite
activities. The code for this example is also available in the 03 CustomActivities solution.
To begin, you create a custom activity that has a property that will default to the current date/time. You will
allow that property to be set to another value that could come from another activity in the workflow or a
parameter that is passed to the workflow when it executes. This composite activity will contain a number
of branches — these will be user defined. Each of these branches will contain an enumerated constant that
defines which day(s) that branch will execute. The following example defines the activity and two branches:
DaysOfWeekActivity
SequenceActivty: Monday, Tuesday, Wednesday, Thursday, Friday
SequenceActivity: Saturday, Sunday
For this example, you need an enumeration that defines the days of the week — this will include the
[Flags] attribute (so you can’t use the built-in DayOfWeek enum defined within the System namespace,
because this doesn’t include the [Flags] attribute).
[Flags]
[Editor(typeof(FlagsEnumEditor), typeof(UITypeEditor))]
public enum WeekdayEnum: byte
{
None = 0x00,
Sunday = 0x01,
Monday = 0x02,
Tuesday = 0x04,
Wednesday = 0x08,
Thursday = 0x10,
Friday = 0x20,
Saturday = 0x40
}
figure 57-12
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