TQueue.Clear Method

Empty queue.

Pascal

procedure Clear;

C++

__fastcall Clear();

Description

Clear removes all entries from the queue. Count is set to 0. This does not change the capacity. This is a O(n) operation where n is the length of the queue.

Note: Clear does not free the items as they are dequeued. If you need to free them, use the OnNotify event, which occurs for every item dequeued and provides the dequeued item.

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;