Expandability
Certain complex properties are capable of being expandable in the property grid. Categories will auto-expand by default, while expandable properties will not auto-expand by default. This behavior can be changed in several ways.
Determining Property Expandability
The PropertyExpandability option helps guide if and when a property is deemed expandable. The PropertyExpandability enumeration returned by that property has these values:
| Value | Description |
|---|---|
Default |
Indicates that properties will be expandable if the associated type converter allows sub-properties to be retrieved. |
None |
Indicates that properties will never be expandable. |
ForceSimple |
Indicates that properties will be forced to be expandable if a custom type converter has not been specified. |
ForceAlways |
Indicates that properties will be forced to be expandable even if a custom type converter has been specified. If a custom type converter has been specified, then it will only be overridden if it does not allow the property to be expandable. |
Most properties aren't expandable, however they can be expandable if their current value has sub-properties of its own. In that case, the expandability option above governs if a property is expandable.
For the Default case, assigning a TypeConverter that is or inherits ExpandableTypeConverter onto the object type will allow it to be expandable based on the expandability setting.
This code shows how to mark a class as expandable via ExpandableTypeConverter:
[TypeConverter(typeof(ExpandableObjectConverter))]
public class Foo {
...
}
Category Auto-Expansion
Categories auto-expand by default, revealing the properties within them. The AreCategoriesAutoExpanded property can be set to false to not auto-expand categories.
Property Auto-Expansion
Expandable properties don't auto-expand by default. The ArePropertiesAutoExpanded property can be set to true to auto-expand all expandable properties.
Selectively Expanding Categories or Properties
Data factories generate the data models (categories, properties, etc.) that the property grid consumes when building its user interface. The IDataModel.IsExpanded property determines if a data model is expanded. It defaults to false, but as mentioned above, the AreCategoriesAutoExpanded and ArePropertiesAutoExpanded properties can alter the defaults for categories and properties respectively.
There may be certain scenarios where you wish to only expand certain categories or properties. In these cases, set AreCategoriesAutoExpanded or and ArePropertiesAutoExpanded (whichever is appropriate) to false and then make a custom data factory.
In the WPF platform, the custom data factory should inherit TypeDescriptorFactory. Override the CreatePropertyModel or CreateCollectionPropertyModel methods as appropriate and call their base methods. If the IPropertyModel result is for a property that should be expanded, set its IsExpanded property to true.
Note that you could alternatively add this logic in a more generalized GetDataModels method override. In that case, call the base method and iterate through the IPropertyModel results. Look for properties that should be expanded and set their IsExpanded properties to true.