在窗体上移动按钮时发生Delphi访问冲突

Question

I am trying to move 2 buttons on the form using a while loop checking for the buttons left property, but I have an Access Violation. I am exeting the procedure with CreateThread()

The code:

procedure AnimButton1();
var ImageCount: integer;
var b1, b2: integer;
begin

  try

       while (b2 <> 187) do
       begin
           b2 := frmNotification.btnBuzina2.Left;
           frmNotification.btnBuzina2.Left := b2 - 1;

       end;

       while (b1 <> 256) do
       begin
           b1 := frmNotification.btnBuzina.Left;
           frmNotification.btnBuzina.Left := b1 - 1;

       end;

  except;
  end;

end;

BUT, when I use a Sleep() with at least 5 miliseconds, I dont have an access violation, like this:

procedure AnimButton1();
var ImageCount: integer;
var b1, b2: integer;
begin

  try

       while (b2 <> 187) do
       begin
           b2 := frmNotification.btnBuzina2.Left;
           frmNotification.btnBuzina2.Left := b2 - 1;
           Sleep(5);
       end;

       while (b1 <> 256) do
       begin
           b1 := frmNotification.btnBuzina.Left;
           frmNotification.btnBuzina.Left := b1 - 1;
           Sleep(5);
       end;

  except;
  end;

end;

Could someone help me to find out why without the sleep I get the access violation and with it I dont?

thx in advance!

Answer 1

I am executing the procedure with CreateThread() .

That is your problem. VCL code must only be called from the main UI thread. Use TThread.Synchronize to invoke the VCL code on the main thread.

That said, a timer might be a more appropriate solution to you problem than a thread.