Using controls in the way of inheritance in Delphi

Before writing code, always make the main unit full brim; Now more like the control more independent function as a unit, overwriting properties, overloaded methods ... Even if only a little bit and the default is different, also like to be independent. Just use the Tlistbox, you need to be able to drag elements, double-click Delete.

Unit ListBox2;
 
Interfaceuses
  system.classes, Vcl.controls, Vcl.stdctrls, system.types;
 
Type
  TListBox2 = Class (Tcustomlistbox)
  protectedprocedure DragOver (source:tobject; X:integer; Y:integer; State:tdragstate; var 

accept:boolean); Override;procedure DblClick; Override;
  Publicconstructor Create (aowner:tcomponent); Override;procedure DragDrop (source:tobject; X: 

Integer; Y:integer); Override;
  End;
 
implementation{TListBox2}constructor tlistbox2.create (aowner:tcomponent);
Begin
  inherited;
  DragMode: = dmautomatic;
End;
 
Procedure Tlistbox2.dblclick;
Begin
  inherited;
  Items.delete (itemindex);
End;
 
Procedure Tlistbox2.dragdrop (Source:tobject; X, Y:integer);
Begin
  inherited;
  Items.exchange (ItemIndex, Itematpos (Point (X,y), True);
End;
 
Procedure Tlistbox2.dragover (Source:tobject; X, Y:integer; State:tdragstate; var Accept: 

Boolean);
Begin
  inherited;
  Accept: = True;
End;
 
End.

Test:

Uses ListBox2;
 
Procedure Tform1.formcreate (sender:tobject);
Begin with
  tlistbox2.create (self) dobeginparent: = self;
    Align: = Alleft;
    Items.commatext: = ' a,b,c,d,e,f,g ';
  End;
End