How to see if a Delphi component already exists in your application?

Question

How does one test if a component exists in your current application for example if you create a dynamic radiogroup named radiogroup1 how do you check if there already is a component with the name radiogroup1?

Answer 1

First you'll have to make a list of all forms in the application.

Then you'll have to search each form for your component using FindComponent.
Here's some sample code:

Something like this:

function TForm1.FindMyComponent(Parent: TComponent; Name: string): TComponent;
var
  i: integer;
begin
  if Parent.ComponentCount = 0 then exit(nil);
  Result:= Parent.FindComponent(Name);
  if Assigned(Result) then Exit;
  for i:= 0 to Parent.ComponentCount do begin
    Result:= FindMyComponent(Parent.Components[i], Name);
    if Assigned(Result) then Exit;
  end; {for i}
end;  

If you call it like this:

procedure TForm1.Test;
var
  MyRadioGroup: TComponent;
begin
  MyRadioGroup:= FindMyComponent(Application, 'RadioGroup1');
  ....
end;

It will recursively look though all registered forms in the application for your radiogroup. See: http://docwiki.embarcadero.com/Libraries/XE2/en/System.Classes.TComponent.FindComponent

Note that the search is not case sensitive.

Do your own bookkeeping
Of course this code will be quite slow if you're looking for lots of controls in this manner.
Also as David stated it does not make sense to attach names to controls you create programmatically. Its better to just keep a list of the control names in a Dictionary and refer to them in that way.

type
  TControlClass = class of TControl;

TForm1 = class(TForm)
private
  NewIndex: TDictonary<string, integer>;
  AllControls: TDictonary<string, TControl>;
....

function TForm1.AddControl(NewControl: TControl);
var
  ClassName: string;
  Index: integer;
  ControlName: string;
begin
  ClassName:= NewControl.ClassName;
  if not(NewIndex.TryGetValue(ClassName, Index) then Index:= 0;
  Inc(Index);
  NewIndex.AddOrSetValue(ClassName, Index);
  ControlName:= ControlName + IntToStr(Index); 
  NewControl.Name:= ControlName;                  //optional;
  AllControls.Add(ControlName, NewControl);
end;

Answer 2

type
    TFrameClass=class of  TFrame;

procedure TForm1.LoadFrame(CurrentFrame: TFrameClass; Name:String);
var 
Reference:TFrameClass;
Instance:TFrame;
begin
  Instance:=TFrame(FindComponent(Name));
  if  (Instance=nil)  then
  begin
      Reference:=TFrameClass(CurrentFrame);
      Instance:=Reference.Create(Self);
      Instance.Align := alClient;
      Instance.Parent := ClientPanel;
  end
  else
    begin
          Instance.BringToFront;
    end;
end;

procedure TForm1.scGPCharGlyphButton4Click(Sender: TObject);
var  FrameInternalDistribution:TFrameInternalDistribution;
begin
    LoadFrame(TFrameInternalDistribution, 'FrameInternalDistribution');
end;

procedure TForm1.scGPCharGlyphButton2Click(Sender: TObject);
var
  FrameInboxDistribution:TFrameInboxDistribution;
begin
  LoadFrame(TFrameInboxDistribution, 'FrameInboxDistribution');
end;