TBoldElementHandle

Super class to handles that hold a value

Unit: BoldHandles

Declaration

TBoldElementHandle = class(TBoldSubscribableComponent)

Hierarchy

1. TComponent
2. TBoldSubscribableComponent
3. TBoldElementHandle
4. Direct subclasses
5. TBoldAbstractSystemHandle
6. TBoldFormSaver
7. TBoldNonSystemHandle
8. TBoldSystemTypeInfoHandle

Description

The element-handles in Bold (i.e. the subclasses to TBoldElementHandle) are the Delphi IDE programmer's main tool for accessing the domain objects in a system using Bold. The handles themselves have several main functions:

• Holding a value
• Allowing Chained Evaluation of OCL-expressions
• Holding a type, in the case when the value is **nil**

Value

The most important property of a handle is Value which refers to a TBoldElement in the domain object layer of the system. The different types of handles get their value in different ways. The value can be **nil**.

Typing
Each handle also has a number of properties related to the (potential) type of Value. This type information is used both for design-time support (i.e. for the OCL-editor), and by components that change their behavior dynamically depending on the type, such as the grid with automatic columns. There are three basic type properties:

• StaticBoldType: A type that is defined on the handle at design-time, and which therefore is known whether the handle has a value or not.
• DynamicBoldType: The type of Value, and thus **nil** if Value is **nil**.
• BoldType: "The best you can get", i.e. DynamicBoldType if (Value <> **nil**), otherwise StaticBoldType

Bold events

TBoldElementHandle is a subclass of TBoldSubscribableComponent, and can therefore by subscribed to using AddSmallSubscription. A TBoldElementHandle can send the following events:

• beDestroying: Sent when the handle is about to be destroyed
• beValueIdentityChanged: Sent when Value has changed, i.e. when Value points to a new TBoldElement. Also sent if anything influencing BoldStaticType has changed. The event will not be sent if it has previously been sent, and the Value property has not been accessed since then. Note that the event is not send when the contents of Value is changed. This is found out by subscribing to Value itself.

It is important to note that there is a difference between the fact that the Value property changes, and that the contents of the element referred to by Value changes.

Any event leading to a (possible) change in Value will lead to a beValueIdentityChanged event being sent to all the subscribers of the handle.

Any event leading to a possible change of the contents of Value will lead to the subscribers to Value being notified according to their subscriptions.

If a convenient way is needed to subscribe to the Value of a handle, without worrying about these two types of subscriptions, a TBoldPlaceableSubscriber should be used.

Properties

Name	Summary	Notes
BoldType	The type of the Value property, or the static type if Value is nil	read-only
DynamicBoldType	The type of Value, or nil if Value is nil	read-only
StaticBoldType	The type of Value, as defined at design-time.	read-only
StaticSystemTypeInfo	Best static determination of which type system the Value will belong to.	read-only
StrictType	Ensure checking of type for handle.
Value	The value of the handle.	read-only

BoldType

property BoldType: TBoldElementTypeInfo;

The type of the Value property, or the static type if Value is **nil**.

It is primarily intended to be used e.g. by Bold-aware controls that have some dynamic behavior based on the type of the handle they are pointing at, such as the automatic column headers on a grid. BoldType is DynamicBoldType if Value <> **nil**, otherwise it is StaticBoldType.

Bold Events
Since BoldType is a readonly property setting it can't directly give rise to events. The following event will however be sent when the value of the property has changed (or rather may have changed, since it may have "changed" to the same value):

• beValueIndentityChanged: Since BoldType depends on Value and StaticBoldType this event will be sent whenever BoldType can have changed.

The event will not be sent if it has previously been sent, and the Value property has not been accessed since then.

DynamicBoldType

property DynamicBoldType: TBoldElementTypeInfo;

The type of Value, or **nil** if Value is currently **nil**. In most cases BoldType is more interesting.

Bold Events

Since BoldType is a read only property setting it can't directly give rise to events. The following event will however be sent when the value of the property has changed (or rather may have changed, since it may have "changed" to the same value):

• beValueIndentityChanged: Since Dynamic BoldType depends on Value this event will be sent whenever DynamicBoldType can have changed.

The event may not be sent if it has previously been sent, and the Value property has not been accessed since then.

StaticBoldType

property StaticBoldType: TBoldElementTypeInfo;

The type of Value, as defined at design-time. Different concrete subclasses of TBoldElementHandle get their static type in different ways. For each handle type this is described on the overview of the class.

Bold events

Since StaticBoldType is a read only property setting it can't directly give rise to events. The following event will however be sent when the value of the property has changed (or rather may have changed, since it may have "changed" to the same value):

• beValueIndentityChanged: Will be sent whenever the conditions defining StaticBoldType have changed.

StaticSystemTypeInfo

property StaticSystemTypeInfo: TBoldSystemTypeInfo;

For all TBoldNonSystemHandles it is determined from StaticSystemHandle if given, otherwise the SystemTypeInfo of the DefaultBoldSystemHandle is used.

This property is mainly intended for the internal use of the handle when defining StaticBoldType and for property-editors used in defining the type.

StrictType

property StrictType: Boolean;

Enforce type on handle. If StrictType is true, an exception will be raised if DynamicBoldType of the handle is not a subtype of StaticBoldType.

Warning

This property has not been implemented yet

Value

property Value: TBoldElement;

The Value of the handle is always a TBoldElement. Different concrete subclasses of TBoldElement get their value in different ways. For each handle type this is described on the overview of the class.

A TBoldElementHandle will always subscribe to beDestroying of its Value (regardless of how it is obtained), so that if the element is removed, Value will be set to **nil**, and a beValueIdentityChanged will be sent to all subscribers of the handle.

Bold events

Since Value is a read only property (for all subclasses except TBoldReferenceHandle), setting it can't directly give rise to events. The following event will however be sent when the value of the property has changed (or rather may have changed, since it may have "changed" to the same value):

• beValueIndentityChanged: Sent when Value has changed, i.e. when Value points to a new TBoldElement.

Note

Note that the event is not send when the contents of Value is changed. This is found out by subscribing to Value itself.

The event will not be sent if it has previously been sent, and the Value property has not been accessed since then.

Methods

Name	Summary	Notes
Destroy	Destroys an instance of a TBoldElementHandle	override
GetStaticBoldType	Get-method for the StaticBoldType property	protected, abstract
GetStaticSystemTypeInfo	Get-method for the StaticSystemTypeInfo property	protected, abstract
GetValue	Get-method for the Value property	protected, abstract
RefersToComponent	Used to determine relationships between a TBoldElementHandle and the component passed as parameter	virtual
StaticBoldTypeChanged	Bold-internal	protected, virtual

Destroy

destructor Destroy; override; See also Ancestor Method

Destroy destroys an instance of TBoldElementHandle. Do not call Destroy directly, use Free instead.

GetStaticBoldType

function GetStaticBoldType: TBoldElementTypeInfo; virtual; abstract;

Get-method for the StaticBoldType property

GetStaticSystemTypeInfo

function GetStaticSystemTypeInfo: TBoldSystemTypeInfo; virtual; abstract;

Get-method for the StaticSystemTypeInfo property

GetValue

function GetValue: TBoldElement; virtual; abstract;

Get-method for the Value property

RefersToComponent

function RefersToComponent(Component: TBoldSubscribableComponent): Boolean; virtual;

RefersToComponent is used internally to avoid circular relations between handles and other components.

StaticBoldTypeChanged

procedure StaticBoldTypeChanged; virtual;

Bold-internal

---

Generated from the Bold 4.0 help (Help/BfD.chm) by Tools/chm2mkdocs.py; member lists reflect Bold 4.0, see the source for members added since.