Question

I have a Delphi7 Project with about 10 windows. The MainWindow gets loaded when the program starts. After a while, the MainWindow accesses another window of the project to add listview items and updates them about ever 1-2 seconds. However this window seems to freeze and doesn’t show the listview at all after I opened it.

It works if I have in the OnShow Procedure of my MainWindow the following commands:

SecondWindow.Show;
SecondWindow.Close;

It works without problems but it seems unprofessional. Any Ideas how I could draw the window without getting showed?

EDIT: CODE (I use Indy9)

procedure TMainWindow.ServerSocketExecute(AThread: TIdPeerThread);
begin
 /....
 if Buffer = 'additem' then begin
    Window2.ListView1.Items.Add;
    Exit;
    // .....
 end;
end;

That’s it. I removed all the timers off Window2 and it seems still to freeze.
Either the mainWindow freezes instantly if an items gets added or when I try to open the 2nd Windows for the first time.

Answer 1

Your problem is that you are calling VCL methods from outside the main GUI thread, i.e. in TMainWindow.ServerSocketExecute. This event executes in a worker thread. Calling VCL/GUI code from a worker thread is simply against the rules of the game. All VCL code must execute in the main GUI thread.

So, solve the problem by making sure that all VCL/GUI code executes in the GUI thread. Use the TIdPeerThread.Synchronize() method, or the TIdSync or TIdNotify class to achieve this.

_{Thanks to @Remy for supplying the details that I did not know.}