7: Constraints and Validation in Visual C#.NET

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7: Constraints and Validation
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one of the ValidationCategory values, but ValidateCustom()takes one or more simple strings to denote a named grouping of validation methods, for instance, MyValidations
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Validation Controller
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Validate()
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Invoke() Validation Method
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Collection <ValidationMessage>
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Validation Observer
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Figure 7-2: Architecture of the validation framework
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Below you can see the set of overrides available for both types; the nonvirtual methods are simply wrappers to call the matching virtual method All methods return true if no validation messages have been logged
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public virtual bool Validate(IEnumerable<ModelElement> subjects, ValidationCategory category); public bool Validate(ModelElement subject, ValidationCategory category); public bool Validate(Partition partition, ValidationCategory category); public bool Validate(Store store, ValidationCategory category); public virtual bool ValidateCustom(IEnumerable<ModelElement> subjects, params string[] customCategories); public bool ValidateCustom(ModelElement subject, params string[] customCategories); public bool ValidateCustom(Partition partition, params string[] customCategories);
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Soft Constraints in the DSL Tools
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public bool ValidateCustom(Store store, params string[] customCategories);
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You can choose to validate either a list or a single ModelElement, the entire content of a Partition or a complete Store When any of the properties of the validation node in the DSL explorer are set to true, a ValidationController object is generated as a member of your designer s DocData class along with a property called ValidationController used to access it Here, then, is an example of code in a custom command to initiate validation Typically, you might manipulate the current UI selection to get a set of ModelElements to validate In this example we ve picked out any PresentationElements or ModelElements that are directly selected and asked for them to be validated using the two custom categories Category1 and Category2 Note how the standard CommandSet base class provides access to the current DocData and thus to the ValidationController in its CurrentData property:
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internal partial class CommandSet { internal void OnMenuCustomValidate(object sender, EventArgs e) { List<ModelElement> toValidate = new List<ModelElement>(); foreach (object selected in thisCurrentSelection) { if (selected is PresentationElement) { toValidateAdd((selected as PresentationElement)ModelElement); } else if (selected is ModelElement) { toValidateAdd(selected as ModelElement); } } if (toValidateCount > 0) { thisCurrentDataValidationControllerValidateCustom( toValidate, "Category1", "Category2"); } } }
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7: Constraints and Validation
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We ve already seen how to mark validation methods to run when a standard category is invoked using the ValidationMethod attribute To mark them for invoking with a custom category, use the named parameter Custom on the ValidationMethod attribute:
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[ValidationMethod(Custom="MyValidations")]
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If needed, you can combine this with one or more of the standard categories:
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[ValidationMethod(ValidationCategoryMenu, Custom="MyValidations")]
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If you need to mark a validation method as being part of more than one custom category, then you can place multiple attributes on the method It is worth noting that the reflective code for determining which methods are validation methods is set up to do efficient caching to minimize its performance impact, especially at designer startup time
Inheriting Validation Behavior By default, validation methods are inherited from their base classes when an inheritance hierarchy of domain classes is used in a model This means that validation can be shared as common behavior, just as any other aspect of a base class The behavior of the ValidationState attribute is, however, different By default, it is not inherited and must be set as Enabled or Disabled on every class It can, however, be forced to inherit its value using the special value Inherited
[ValidationState (ValidationStateInherited)] public partial class SomeDerivedDomainClass { }
Validation Output The output of validation is a collection of ValidationMessage objects that are sent to all of the ValidationObserver objects that the ValidationController knows about By default, the generated designer code uses a Visual Studio speci c subclass, VsValidationController, and is set up with a single observer The generated initialization code looks like this:
Soft Constraints in the DSL Tools
validationController = new VsValidationController(thisServiceProvider); errorListObserver = new ErrorListObserver(thisServiceProvider); validationControllerAddObserver(thiserrorListObserver);
You can add your own extra observers by deriving a class from ValidationObserver to send ValidationMessages to your own custom UI, logger, or database and then calling the AddObserver() method on the controller The ErrorListObserver class presents ValidationMessages that it receives in the Visual Studio error list window (Figure 7-3)