Custom Activity to Switch on a Range of Values

  • Article

This topic applies to Windows Workflow Foundation 4 (WF4).

This sample demonstrates how to create a custom activity that extends the use of a Switch. A conventional Switch statement allows switching based upon a single value. But, there are business scenarios where an activity must switch based upon a range of values. For example, an activity might execute one action when the value being switched upon is between 1 and 5, another action when the value is between 6 and 10, and a default action for all other values. This custom activity enables exactly that scenario.

The SwitchRange Activity

The SwitchRange activity schedules a child activity when the result value of its expression is included within the range of one of its Cases.

The following code example is a custom activity that switches based upon a range of values.

public sealed class SwitchRange<T> : NativeActivity where T : IComparable
{
   [RequiredArgument]
   [DefaultValue(null)]
   public InArgument<T> Expression { get; set; }

   public IList<CaseRange<T>> Cases

   [DefaultValue(null)]
   public Activity Default { get; set; }}
}

Property

Description

Expression

This is the expression to be evaluated and compared against the ranges in the Cases list. The result of the expression is of type T.

Cases

Each case consists of a range (From and To) and an activity (Body). The expression is evaluated and compared against the ranges. If the result of the expression is within the range of one of the cases, the corresponding activity is executed.

Default

The activity that is executed when no case is matched. When set to null, no action is taken.

CaseRange Class

The CaseRange class represents a range within a SwitchRange activity. Every instance of CaseRange contains a range (composed of a From and a To) and a Body activity that is scheduled if the expression in the SwitchRange is evaluated within the range.

The following code example is the definition for the CaseRange class.

public class CaseRange<T> where T : IComparable
{
    public T From { get; set; }

    public T To { get; set; }

    public Activity Action { get; set; }
}

Note

Both the SwitchRange and CaseRange classes, which are defined in the sample are generic classes that can work with any type that implements IComparable, like the Switch class.

Sample Usage

The following code example demonstrates how to use the SwitchRange activity.

Activity SwitchRange = new SwitchRange<int>
{
    Expression = new InArgument<int>(value),
    Cases = 
    {
        new CaseRange<int>                    
        {
            From = 1,
            To = 5,
            Action = new WriteLine
            {
                Text = "Case 1-5 selected",
            }
        },
        new CaseRange<int>
        {
            From = 6,
            To = 10,
            Action = new WriteLine
            {
                Text = "Case 6-10 selected",
            }
        }
    },
    Default = new WriteLine { Text = "Default Case selected" }
};

To use this sample

  1. Using Visual Studio 2010, open the SwitchRange.sln solution file.

  2. To build the solution, press CTRL+SHIFT+B.

  3. To run the solution, press CTRL+F5.

Dd797581.Important(en-us,VS.100).gif Note:
The samples may already be installed on your computer. Check for the following (default) directory before continuing.

<InstallDrive>:\WF_WCF_Samples

If this directory does not exist, go to Windows Communication Foundation (WCF) and Windows Workflow Foundation (WF) Samples for .NET Framework 4 to download all Windows Communication Foundation (WCF) and WF samples. This sample is located in the following directory.

<InstallDrive>:\WF_WCF_Samples\WF\Scenario\ActivityLibrary\SwitchRange