TQueue.Enqueue Method

Add item to end of queue.

Pascal

procedure Enqueue(const Value: T);

C++

__fastcall Enqueue(const T Value);

Description

Enqueue adds the given item Value to the end of the queue. You can enqueue nil. Count is incremented by 1. If Count is at capacity, the queue size is automatically increased. Count is incremented by 1.

An OnNotify event occurs indicating an item was added to the queue.

This is a O(1) operation, unless the capacity must increase. In this case, it is O(n), where n is Count.

Delphi Examples:

Copy Code

{
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;