Duplicating components and their children at runtime

The following code provides a function called DuplicateComponents that duplicates any given component and its child components at run time. It tries to emulate copying and pasting a component at design time. The new component is created with the same parentage and owner as the original and all new component names are similar (but different) to their original. This is provided as is and may have bugs that I haven't found yet. It is provided because it contains techniques that are not commonly known and may be of use to people struggling with similar problems.

This procedure is very useful when you want to design a section of an interface once that will appear n times at run time. You just design it once visually all on a TPanel or other component as a parent, and then do "newpanel := DuplicateComponents(designedpanel)".

uses

SysUtils, Windows, Messages, Classes, Graphics, Controls,

Forms, Dialogs, ExtCtrls, StdCtrls, IniFiles, TypInfo, Debug;

type

TUniqueReader = Class(TReader)

LastRead: TComponent;

procedure ComponentRead(Component: TComponent);

procedure SetNameUnique(

Reader: TReader;

Component: TComponent;

var Name: string

);

end;

implementation

procedure TUniqueReader.ComponentRead(

Component: TComponent

);

begin

LastRead := Component;

end;

procedure TUniqueReader.SetNameUnique( // sets the name of the read

component to something like "Panel2" if "Panel1" already exists

Reader: TReader;

Component: TComponent; // component being read

var Name: string // Name to use and modify

);

var

i: Integer;

tempname: string;

begin

i := 0;

tempname := Name;

while Component.Owner.FindComponent(Name) <> nil do begin

Inc(i);

Name := Format('%s%d', [tempname, i]);

end;

function DuplicateComponents(

AComponent: TComponent // original component

): TComponent; // returns created new component

procedure RegisterComponentClasses(

AComponent: TComponent

);

var

i : integer;

begin

RegisterClass(TPersistentClass(AComponent.ClassType));

if AComponent is TWinControl then

if TWinControl(AComponent).ControlCount > 0 then

for i := 0 to

(TWinControl(AComponent).ControlCount-1) do

RegisterComponentClasses(TWinControl(AComponent).Controls[i]);

end;

var

Stream: TMemoryStream;

UniqueReader: TUniqueReader;

Writer: TWriter;

begin

result := nil;

UniqueReader := nil;

Writer := nil;

try

Stream := TMemoryStream.Create;

RegisterComponentClasses(AComponent);

try

Writer := TWriter.Create(Stream, 4096);

Writer.Root := AComponent.Owner;

Writer.WriteSignature;

Writer.WriteComponent(AComponent);

Writer.WriteListEnd;

finally

Writer.Free;

end;

Stream.Position := 0;

try

UniqueReader := TUniqueReader.Create(Stream, 4096); // create reader

// should probably move these routines into theconstructor

UniqueReader.OnSetName := UniqueReader.SetNameUnique;

UniqueReader.LastRead := nil;

if AComponent is TWinControl then

UniqueReader.ReadComponents(

// read in components and sub-components

TWinControl(AComponent).Owner,

TWinControl(AComponent).Parent,

UniqueReader.ComponentRead

)

else

UniqueReader.ReadComponents(

// read in components

AComponent.Owner,

nil,

UniqueReader.ComponentRead

);

result := UniqueReader.LastRead;

finally

UniqueReader.Free;

end;

finally

Stream.Free;

end;