#include using namespace Upp; struct App : TopWindow { Thread work; ArrayCtrl list; typedef App CLASSNAME; App(); ~App(); }; App::App() { list.AddColumn("Test"); Add(list.SizePos()); work.Run([=] { for(;;) { Sleep(1); GuiLock __; // After locking GuiLock __, access is allowed to GUI object except opening/closing windows if(IsShutdownThreads()) break; if(list.GetCount() > 100) { bool quit; Ptr p = this; Call([=, &quit] { if(p) // check whether App still exists (e.g. can be closed by close button) quit = PromptYesNo("Quit?"); }); // quit = PromptYesNo("Quit?"); // (but Prompt has this ability already implemented, so direct call would work too) if(quit) { Break(); return; } list.Clear(); } list.Add((int64)Random()); } }); } App::~App() { ShutdownThreads(); } GUI_APP_MAIN { App app; app.Run(); }