The Problem Solver

Validating custom activities in the Workflow designer

Create a derived class from ActivityValidator and add it to your custom activity using the ActivityValidatorAttribute. For example:

[ActivityValidator(typeof(ValidatedActivityValidator))]
public partial class ValidatedActivity : SequenceActivity
{
}

The validator class now look like this:

class ValidatedActivityValidator : ActivityValidator
{
    public override ValidationErrorCollection Validate(ValidationManager manager, object obj)
    {
        ValidationErrorCollection result = base.Validate(manager, obj);

        ValidatedActivity activity = obj as ValidatedActivity;
        if (activity != null && activity.Parent != null)
        {
            if (activity.AValueBetween1And250 < 1)
                result.Add(
                    new ValidationError("The value is to small", 
                        102, false, "AValueBetween1And250"));

            if (activity.AValueBetween1And250 > 250)
                result.Add(
                    new ValidationError("The value is to big", 
                        103, true, "AValueBetween1And250"));
        }

        return result;
    }
}

Note that the object parameter (obj) is the activity to be validated.

The ActivityValidator type contains two virtual function Validate and ValidateProperties. It doesn't really matter which you use as the Validate actually calls the ValidateProperties function. This means they are both called at the same time unless you change the behavior by not calling the base.Validate() function.

To indicate errors or warnings you can add a ValidationError object to the ValidationErrorCollection to be returned. Adding the property name makes life easy on the developer using your activity because it allows the designer to automatically select the property by double clicking the error.

Another thing to keep in mind is that the validator will be called when the activity itself is compiles. To see if this is the case check the activity Parent class which will be null.

The validator is also called when the workflow is executed allowing for runtime property checking.

Enjoy!

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