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opInsert

opInsert = 0

Example​

function IsInsertionNotification(Operation: TOperation): Boolean;
begin
  Result := Operation = opInsert;
end;

Usage​

opInsert identifies a Velox component notification sent after a component has been inserted into an owner's component list.

Additional Technical Info​

opInsert is the first value in Delphi's TOperation enumeration. It tells notification-handling code that a component has just been inserted into an owner's component list. Velox registers TOperation as a hidden scripting type, while exposing its two constants for comparisons and for APIs whose signatures use the type.

The example only classifies a received value. Comparing a value with opInsert does not insert, own, create or initialise a component.

Exact lifecycle position

In the current Delphi implementation, TComponent.InsertComponent performs these operations before it sends this notification:

  1. asks an attached designer whether insertion is permitted;
  2. validates that the component can be contained by the proposed owner;
  3. removes it from any previous owner;
  4. validates that its name is empty or unique in the new owner;
  5. inserts it into the new owner's component collection;
  6. establishes the component reference and propagates design state when applicable; and
  7. calls the owner's Notification(AComponent, opInsert).

Consequently, notification code observes the component after its owner/list relationship has changed. It must not treat the callback as a cancellable before insert event. Earlier validation can raise an exception; if that happens before insertion completes, no opInsert notification is sent by this path.

The base TComponent.Notification implementation forwards the notification through the owner's current component tree. It iterates defensively because a callback can change that collection. Overrides should perform minimal work and preserve inherited propagation unless they deliberately replace the component framework contract.

Velox-specific behavior and quirks

Velox's internal TvxNotification helper translates opInsert to its OnAdd callback. However, its public Subscribe method uses Delphi FreeNotification, which registers for destruction/removal notification and does not itself insert the subscribed component into an owner. A subscription therefore normally produces opRemove when the component is destroyed, not an opInsert event. Do not interpret OnAdd as proof that Subscribe was called.

Most Velox source consumers use opRemove to clear dependencies; there is no corresponding product-wide rule that every reference assignment emits opInsert. Component-property assignment, ownership insertion and free-notification registration are separate mechanisms.

Side effects, errors and performance

The enumeration value has no side effects and comparison is constant-time. The operation that generated it may have already changed ownership and may have invoked other notification handlers. Component ownership and notification lists are mutable framework state, not a thread-safe event bus; process them on the component's owning thread and avoid blocking, recursive ownership changes or retaining unverified references.

External references

Created 2026-07-15