Controlling the Visibility of an Icon or Decorator

Article
04/28/2015

A decorator is an icon or line of text that appears on a shape in a domain-specific language (DSL). You can make the decorator appear and disappear depending on the state of properties in the model. For example, on a shape representing a Person, you could have different icons that appear depending on the person's gender, number of children, and so on.

Controlling the visibility of an icon or decorator

The following procedure assumes that you have already defined a shape and its mapping to a domain class. For more information, see How to Define a Domain-Specific Language.

To control the visibility of an icon or text decorator

In the DSL Definition diagram, add to the shape class the icons or text decorators that you want to appear.
1. Right-click the shape class, point to Add, and then click the required type of decorator.
2. Set the decorator's Position property. More than one decorator can have the same position. For example, you could have icons for male and female sharing the same position.
3. Set the Default Icon property of an icon decorator.
Select the diagram element map, which is the gray line between the shape class and the domain class on the DSL Definition diagram.
In the DSL Details window, in the Decorator Maps tab, select a decorator. For example, the MaleDecorator.
Check the Visibility Filter box.
If the domain property that should control visibility is on the immediate domain class, leave Path to Filter Property blank.

Otherwise, click the drop-down menu and navigate to the relationship or class where the property is located.
- To avoid an error report, you should not navigate through a relationship marked with "*" in the navigation tool.
Set the Filter Property to a domain property. For example, Gender.
In the Visibility Entries list, add values of this domain property for which the decorator should be visible. For example, Male.
Repeat the steps for each icon.
Transform All Templates, build and run, and open a test diagram.
When you change the controlling property value, the decorators should appear and disappear.

Frequently, you want visibility to be controlled by a more complex formula than a simple set of values. For example, to have an icon depend on the number of links of a particular type, or to make it depend on a whether a number is in a particular range. In that case, use the following procedure.

To control the visibility of a decorator based on a formula

Add a calculated domain property to the domain class. In the Properties window, set the following values:

IsBrowsable = False - this hides the property from the user

Kind = Calculated - this means that you will provide code that calculates its value

Name for example DecoratorControl

Type = Boolean

For more information, see Calculated and Custom Storage Properties.
Make the new property control the decorator visibility.
1. Select the diagram element map, which is the gray line from the domain class to the shape. In the DSL Details window, open the DecoratorMap tab.
2. Check the Visibility Filter box.
3. In Filter Property, select the control property DecoratorControl.
4. Under Visibility Entries, enter True.
Click Transform All Templates in the Solution Explorer toolbar.
Click Build Solution on the Build menu.
Double-click the error report that has appeared: "YourClass does not contain a definition for GetDecoratorControlValue ...".

The text editor opens on Dsl\GeneratedCode\DomainClasses.cs. Above the highlighted error is a comment that requests you to add a method.
Note the namespace, class and method that are missing. For example, Company.FamilyTree.Person.GetDecoratorControlValue().
In a separate code file, write a partial class definition that contains the missing method. For example:
```
namespace Company.FamilyTree
{ partial class Person
  { bool GetDecoratorControlValue()
    {
      return this.Children.Count > 0;
} } }
```
For more information about customizing the model with program code, see Navigating and Updating a Model in Program Code.
Rebuild and run the solution.

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Controlling the Visibility of an Icon or Decorator