Adressing multiple, similar variables/objects in Delphi

Question

I am writing a program that uses many shapes and I need to create a procedure to turn them all white. The shapes in question are named SectorBorder1 to SectorBorder20.

Is there a way to adress the shapes like this or similarly?

SectorBorder[X].brush.color := ClWhite;
Inc(X);

...where X is the number (obviously), instead of having to do:

SectorBorder1.brush.color := ClWhite;
SectorBorder2.brush.color := ClWhite;
...
SectorBorder20.brush.color := ClWhite;

So basically being able to differentiate names through a variable. This is the only way I could think of describing it. (Sorry, could someone also maybe include a better discription?) Any advice would be greatly apreciated.

You can use an array for this. Or a list.

Andreas Rejbrand
– Andreas Rejbrand

2021-04-28 13:34:18 +00:00
Commented Apr 28, 2021 at 13:34 — Andreas Rejbrand
– Andreas Rejbrand, Commented Apr 28, 2021 at 13:34

Remy Lebeau · Accepted Answer · 2021-04-28 14:26:54Z

4

Use an array

private
  SectorBorders: array[1..20] of TShape;

procedure TMyForm.FormCreate(Sender: TObject):
begin
  SectorBorders[1] := SectorBorder1;
  ..
  SectorBorders[20] := SectorBorder20;
end;

procedure TMyForm.SetAllToWhite;
var
  X: Integer;
begin
  for X := Low(SectorBorders) to High(SectorBorders) do
    SectorBorders[X].Brush.Color := clWhite;
end;

answered Apr 28, 2021 at 14:26

Remy Lebeau

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Comments

Rob Lambden · Accepted Answer · 2021-04-28 20:58:51Z

As an alternative to an array you can use a List. If you use the TList from System.Generics.Containers you can easily pass through all elements of the list.

You use it like this:

interface

uses  System.Generics.Collections;   // you need this to get the TList, you also need your other refereces of course

  ...

  protected
    pShapes:  TList<TShape>;

  procedure TMyForm.FormCreate(Sender: TObject):
  var
    nLoop: Integer;
  begin
    Self.pShapes:=TList<TShape>.Create;
    nLoop:=0;
    while(nLoop<Self.ComponentCount) do
    begin
      if(Self.Components[nLoop] is TShape) then
        pList.Add(TShape(Self.Components[nLoop]));
      Inc(nLoop);
    end;
  end;

  procedure TMyForm.SetAllToWhite;
  var
    pShape:  TShape;
  begin
    for pShape in Self.pShapes do 
      pShape.Brush.Color := clWhite;
  end;

Choosing whether you want to use an array or a TList will be partially down to preference, but also down to what else you may want to do with the collection of TShapes and how they are managed within the object.

Michael Warreyn · Accepted Answer · 2021-04-29 00:41:26Z

1

You can use the FindComponent method of the form.

shape:= FindComponent('SectorBorder' + IntToStr(i)) as TShape;
if shape <> nil then 
   pShape.Brush.Color := clWhite;

See http://docwiki.embarcadero.com/CodeExamples/Sydney/en/FindComponent_(Delphi)

answered Apr 29, 2021 at 0:41

Michael Warreyn

913 bronze badges

3 Comments

HeartWare Over a year ago

Please beware, that if you have a non-TShape component named "SectorBorder99" you'll get an exception at the "as" stage. Safer to first find the component and then check (using "is") if the component you have found is a TShape (or child thereof).

Andreas Rejbrand Over a year ago

Also, in most cases, FindComponent (and referring to components by string names in general) is an antipattern.

HeartWare Over a year ago

Yes - you risk a later developer coming in and renaming/making a new component that suddenly makes your program crash due to an assumption you've put in that (s)he wasn't aware of.

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