How to - Validate Windows Workflow custom activity input
Windows Workflow allow us to perform custom validator input that is executed at design and compile time. The error output is similar as Biztalk Orchestration shape errors.
Adding a validator to a custom activity involves two steps:
- Create a class that derives from ActivityValidator class and override Validate method;
- Add a ActivityValidator attribute with the validator type to the custom activity;
As an example, i'm going to show a validator creation that verifies if a specific property is set.
I have already created a custom activity that is called Hello and have a property that receives the user name. To validate if the activity proprety is set, i'm going to create a validator.
ActivityValidator class creation:
As said early, to create a validator i have to create a class that derives from ActivityValidator. To perform the validation i have to override the validate method and set the validation code.
using System;
using
System.Text.RegularExpressions;
using
System.Workflow.ComponentModel.Compiler;
internal sealed class ExampleValidator : ActivityValidator {
public override ValidationErrorCollection Validate (ValidationManager manager, object obj)
{
if (manager == null throw new ArgumentNullException("Invalid manager.");)
if (obj == null throw new ArgumentNullException("Invalid activity.");)
HelloActivity activity = obj as HelloActivity
if (activity == null) throw new InvalidOperationException("Activity should be a HelloActivity.");
ValidationErrorCollection errors = base.Validate(manager, obj);
// Validate UserName property setting validationErrorCollection with information
// about the property that causes the error.
if (string.IsNullOrEmpty(activity.UserName)) {
errors.Add(ValidationError.GetNotSetValidationError("Username"));
}
return errors;
}
}
Custom activity and validator association
To associate the validator with the custom activity it's used the activityvalidator attribute.
[ActivityValidator(typeof(ExampleValidator))]
public sealed class HelloActivity : System.Workflow.ComponentModel.Activity {..
In the end the custom activity validator error will be show like this:
