RAD Studio VCL Reference
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Remove and return list entry.
function Extract(const Value: T): T;
__fastcall T Extract(const T Value);
Extract removes the entry Value from the list, returning this value. If Value is not in the list, it returns the default value of its type T.
An OnNotify event occurs indicating an entry was removed from the list. Extract is similar to Remove except for the event code indicating an element was extracted rather than removed and is provided so items may be removed without freeing.
Delphi Examples:
{ This example demonstrates the usage of the generic TList class. } procedure TForm3.Button1Click(Sender: TObject); var List: TList<Integer>; FoundIndex: Integer; begin { Create a new List } List := TList<Integer>.Create(); { Register a notification call-back } List.OnNotify := ListChanged; { Add a few values to the list } List.AddRange([5, 1, 8, 2, 9, 14, 4, 5, 1]); MessageDlg('Index of first 1 is ' + IntToStr(List.IndexOf(1)), mtInformation, [mbOK], 0); MessageDlg('Index of last 1 is ' + IntToStr(List.LastIndexOf(1)), mtInformation, [mbOK], 0); MessageDlg('List contains elemnt 100? ' + BoolToStr(List.Contains(100)), mtInformation, [mbOK], 0); { Add another element to the list } List.Add(100); MessageDlg('There are ' + IntToStr(List.Count) + ' elements in the list.', mtInformation, [mbOK], 0); { Remove the first occurence of 1 } List.Remove(1); { Delete a few elements form position 0 } List.Delete(0); List.DeleteRange(0, 2); { Extract the remeining 1 from the list } List.Extract(1); { Set the capacity to the actual length } List.TrimExcess(); MessageDlg('There capacity of the list is ' + IntToStr(List.Capacity), mtInformation, [mbOK], 0); { Clear the list } List.Clear(); { Insert some elements } List.Insert(0, 2); List.Insert(1, 1); List.InsertRange(0, [6, 3, 8, 10, 11]); { Sort the list } List.Sort(); { Binary search for the required element } if List.BinarySearch(6, FoundIndex) then MessageDlg('Found element 6 at index ' + IntToStr(FoundIndex), mtInformation, [mbOK], 0); { Reverse the list } List.Reverse(); MessageDlg('The element on position 0 is ' + IntToStr(List.Items[0]), mtInformation, [mbOK], 0); end; procedure TForm3.ListChanged(Sender: TObject; const Item: Integer; Action: TCollectionNotification); begin { This method is called by the List everytime a change occurs } if Action = cnAdded then MessageDlg('Element added: ' + IntToStr(Item), mtInformation, [mbOK], 0) else if Action = cnRemoved then MessageDlg('Element removed: ' + IntToStr(Item), mtInformation, [mbOK], 0) else if Action = cnExtracted then MessageDlg('Element extracted: ' + IntToStr(Item), mtInformation, [mbOK], 0) end;
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