System.Messaging.TMessageManager.SubscribeToMessage
Delphi
function SubscribeToMessage(const AMessageClass: TClass; const AListener: TMessageListener): TMessageSubscriptionId; overload; virtual;
function SubscribeToMessage(const AMessageClass: TClass; const AListenerMethod: TMessageListenerMethod): TMessageSubscriptionId; overload; virtual;
C++
virtual TMessageSubscriptionId __fastcall SubscribeToMessage(const System::TClass AMessageClass, const _di_TMessageListener AListener)/* overload */;
virtual TMessageSubscriptionId __fastcall SubscribeToMessage(const System::TClass AMessageClass, const TMessageListenerMethod AListenerMethod)/* overload */;
Contents
Properties
| Type | Visibility | Source | Unit | Parent |
|---|---|---|---|---|
| function | public | System.Messaging.pas System.Messaging.hpp |
System.Messaging | TMessageManager |
Description
Subscribes a listener to a message.
Call SubscribeToMessage to subscribe message-handling methods to specific types of messages on a message manager.
To unsubscribe a previously-subscribed method from a message type, call Unsubscribe.
Example
The example below shows how to subscribe an anonymous method. The example subscribes the anonymous method to messages containing an Unicode string. When a message of this type is sent to the message manager, the anonymous method shows a dialog box displaying the string from the message.
In Delphi:
// var SubscriptionId: Integer;
SubscriptionId := MessageManager.SubscribeToMessage(TMessage<UnicodeString>, procedure(const Sender: TObject; const M: TMessage)
begin
ShowMessage((M as TMessage<UnicodeString>).Value);
end);
In C++:
- 1. Define a method in your class with the following signature:
void __fastcall TForm1::ShowReceivedMessage(System::TObject* const Sender, System::Messaging::TMessage* const M)
{
TMessage__1<UnicodeString>* Message = dynamic_cast<TMessage__1<UnicodeString>*>(M);
if (Message)
ShowMessage(Message->Value);
}
- 2. Then subscribe this method as follows:
TMessageManager* MessageManager = TMessageManager::DefaultManager;
TMetaClass* MessageClass = __classid(TMessage__1<UnicodeString>);
TMessageListenerMethod ShowReceivedMessagePointer = &(this->ShowReceivedMessage);
int SubscriptionId = MessageManager->SubscribeToMessage(MessageClass, ShowReceivedMessagePointer);
See Also
- System.Messaging (Delphi) code example
- System.Messaging (C++) code example