RAD Studio VCL Reference
|
Remove top queue item.
function Dequeue: T;
__fastcall T Dequeue();
Dequeue removes and returns the top element of the queue. Count is decremented by 1. If Count is already 0, an error is raised.
An OnNotify event occurs indicating an item was removed from the queue. Dequeue is the same as Extract except for the event code indicating an element was removed rather than extracted.
Dequeue functions similarly to Peek except that Dequeue removes an element from the queue.
This is a O(1) operation.
Delphi Examples:
{ This example demonstrates the usage of the generic TQueue class. } procedure TForm3.Button1Click(Sender: TObject); var Queue: TQueue<String>; begin { Create a new Queue } Queue := TQueue<String>.Create(); { Register a notification call-back } Queue.OnNotify := QueueChanged; { Enqueue some items up the Queue } Queue.Enqueue('John'); Queue.Enqueue('Mary'); Queue.Enqueue('Bob'); Queue.Enqueue('Anna'); Queue.Enqueue('Erica'); { Show the last enqueued element without modifying the Queue } MessageDlg('First enqueued element is: "' + Queue.Peek() + '".', mtInformation, [mbOK], 0); { Extract the top element: "Erica" } Queue.Extract(); { Reduce the capacity } Queue.TrimExcess(); { The remaining count of elements } MessageDlg('The queue contains ' + IntToStr(Queue.Count) + ' elements.', mtInformation, [mbOK], 0); { Show the last enqueued element by modifying the Queue } MessageDlg('First enqueued element is: "' + Queue.Dequeue() + '".', mtInformation, [mbOK], 0); { Clear the Queue } Queue.Clear(); { Destroy the Queue completely } Queue.Free; end; procedure TForm3.QueueChanged(Sender: TObject; const Item: String; Action: TCollectionNotification); begin { This method is called by the List everytime a change occurs } if Action = cnAdded then MessageDlg('Element added: ' + Item, mtInformation, [mbOK], 0) else if Action = cnRemoved then MessageDlg('Element removed: ' + Item, mtInformation, [mbOK], 0) else if Action = cnExtracted then MessageDlg('Element extracted: ' + Item, mtInformation, [mbOK], 0) end;
Copyright(C) 2009 Embarcadero Technologies, Inc. All Rights Reserved.
|
What do you think about this topic? Send feedback!
|