Delphi: TImage.Create causes Access violation

4
votes

I apologize in advance for a newbie question, but why do I get "Access violation" error with the code below (on the "Create(SelectorForm);" line)? I tried using the main form as the owner, but it didn't make any difference.

var
  SelectorForm: TSelectorForm;
  ArrayOfImages: Array [1..10] of TImage;

implementation

procedure TSelectorForm.FormCreate(Sender: TObject);
var
  Loop: Byte;
begin
  for Loop := 1 to 10 do
  begin
    with ArrayOfImages[Loop] do
    begin
      Create(SelectorForm);
    end;
  end;
end;
2
delphiarraysdelphi-7access-violation

2 Answers

17
votes

The problem is that you are effectively doing this:

var
  imageVariable: TImage;
begin
  imageVariable.Create (ParentForm);
end;

Which is wrong because "Create" method is being called on the variable which hasn't been assigned yet.

You should do this:

var
  imageVariable: TImage;
begin
  imageVariable := TImage.Create (ParentForm);
  try
    //use the object
  finally
    FreeAndNil (imageVariable);
  end;
end;

Or more specifically in your code:

for Loop := 1 to 10 do
begin
  ArrayOfImages[Loop] := TImage.Create (Self);
end;

Don't forget to free the objects

EDIT: Accepting @andiw's comment and taking back the tip of freeing objects. EDIT2: Accepting @Gerry's comment and using Self as owner.

0
votes

There are a lot of problems with the above code. (don't use the "With" like that for a start, don't use a Byte for your loop var)

My assumption is that you ultimately want an array of instances of TImage's created with a form as the parent.

so based on that assumtion...you want something like (untested)

var
  ArrayOfImages: Array [0..9] of TImage;  
  i : integer;
begin
  for i := 0 to 9 do
  begin
    ArrayOfImages[i] := TImage.Create(theForm);
  end;

end;

Now note, you will be responsible for cleaning up the array when you are finished using it, you will need to call free on each of the Image instances.