Create objects in runtime and work with them

Question

I'm having problem with object(s) created while my program is running

First I create n objects (let's say that n := 3)

for i:=0 to n-1 do
  begin
    With TGauge.Create(Form1) do
      begin
        Parent  := Form1;  // this is important
        Left    := 20;     // X coordinate
        Top     := 20+i*45;     // Y coordinate
        Width   := 250;
        Height  := 20;
        Kind    := gkHorizontalBar;
        Name    := 'MyGauge'+IntToStr(i);
        //.... 
        Visible := True;
      end;
  end;

These 3 objects are created and visible in the form. Now I want to alter its' property, but whenever I try to access these created object I only get

EAccessViolation

for example when I try to get name of one object

g := Form1.FindComponent('MyGauge0') as TGauge;
Form1.Label1.Caption:=g.Name;

Better store their references into an array, or a list like collection. — TLama
– TLama, Commented Jan 11, 2015 at 14:39
"this is important" I would presume all of your code is important :-) — Jerry Dodge
– Jerry Dodge, Commented Jan 11, 2015 at 18:11

David Heffernan · Accepted Answer · 2015-01-11 14:46:22Z

8

Your code is failing because FindComponent returns nil. That's because the Form1 object does not own a component with that name. Quite why that is so is hard to tell from here.

However, using name lookup is the wrong way to solve your problem. Don't use names to refer to components. Hold their references in an array.

var
  Gauges: array of TGauge;
....
SetLength(Gauges, N);
for I := 0 to N-1 do
begin
  Gauges[i] := TGauge.Create(Form1);
  ....
end;

Then you can refer to the controls using that array.

I would also comment that it is odd that you are referring to the Form1 global object. It would likely be better to do this inside the TForm1 class and so be able to use the implicit Self instance.

edited Jan 11, 2015 at 14:46

answered Jan 11, 2015 at 14:41

David Heffernan

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