Attributes

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New to the .NET framework is the concept of attribute-based development. Attributes provide an extensibility mechanism for classes, properties, methods, parameters, and return values. By applying attributes to a particular entity, the default behavior can be altered to produce a new desired result. For a complete description of attributes, refer to the MSDN help.

The .NET designer architecture makes heavy use of attributes to simplify common development tasks. Examples include defining the default value for a property, assigning a category and description to properties, and indicating the default event for a control, to name a few. No discussion of the designer architecture would be complete without a list of attributes commonly used for designers, controls, serialization, licensing, and the PropertyGrid. Table 5.12 lists the attributes found in the System.ComponentModel namespace, along with descriptions.

Table 5.13 and Table 5.14 list the attributes found in the System.ComponentModel.Design.Serialization and System.Drawing namespaces, respectively.

Table 5.12. System.ComponentModel Attributes

Attribute	Description
AmbientValueAttribute	The value for this property originates for another source, generally the containing control.
BrowsableAttribute	Used by the PropertyGrid to determine whether the property should be displayed.
CategoryAttribute	Defines the category for the property or event within the PropertyTab of the PropertyGrid.
DefaultEventAttribute	Defines the default event for the component.
DefaultPropertyAttribute	Defines the default property for a component.
DefaultValueAttribute	Defines the default value for a property.
DescriptionAttribute	Defines the description for the property or event.
DesignerAttribute	Identifies the designer for the specified component.
DesignerCategoryAttribute	Defines the category for the designer.
DesignerSeralizationVisibiltyAttribute	Specifies how the designer should serialize a property.
DesignOnlyAttribute	Specifies that the property is available only at design-time.
EditorAttribute	Specifies the UITypeEditor for the component property.
EditorBrowsableAttribute	Specifies whether the property is available to the UITypeEditor.
ImmutableObjectAttribute	Specifies that the component has no editable properties.
LicenseProviderAttribute	Specifies the LicenseProvider for the class.
ListBindableAttribute	Specifies a list can be used for data binding.
LocalizableAttribute	Localization for a property.
MergablePropertyAttribute	Specifies that a property can be combined with properties of other objects in the property window.
NotifyParentPropertyAttribute	Specifies that the parent property should be notified when the property is modified.
ParenthesizePropertyNameAttribute	Specifies that the property value should appear within a set of parentheses. Example: (Collection) appears next to collection-based properties such as the Tabs property of the Tab control.
PropertyTabAttribute	Identifies the property tab(s) to display for the class or classes.
ProvidePropertyAttribute	Defines the name of a property provided by the class that implements the IExtenderProvider interface. The ToolTip class is an extender provider.
ReadOnlyAttribute	Specifies that the property is read-only within the PropertyGrid.
RecommendedAsConfigurableAttribute	Specifies that the property can be used as an application setting.
RefreshPropertiesAttribute	Defines how the designer refreshes when the property is modified.
ToolboxItemAttribute	Specifies whether the component should be loaded in the toolbox.
ToolboxItemFilterAttribute	Specifies that the component will accept only other ToolboxItems belonging to the specified namespace, or type.

Table 5.13. System.ComponentModel.Design.Serialization Attributes

Attribute	Description
DesignerSerializerAttribute	Indicates the serializer for the serialization manager to use in order to serialize objects of this type.
RootDesignerSerializer	Indicates the base serializer for the root object designer.

Table 5.14. System.Drawing Attributes

Attribute	Description
ToolboxBitmapAttribute	Associates an image with the specified component. Support for small and large images.

Attributes are a prominent theme in .NET development, and custom control development is no exception.