Add option to prevent application shutdown

This update allows the application shutdown to be cancelled. It implements the shouldQuit function, which can prevent the application from quitting if it returns false. Additional checks have been added to ensure cleanup and quit processes are performed only if required. The darwin delegate and linux and windows applications were modified to include this new functionality.

v3/pkg/application/application.go

@@ -297,6 +297,7 @@ type App struct {
 
 	// Shutdown
 	performingShutdown bool
+
 	// Shutdown tasks are run when the application is shutting down.
 	// They are run in the order they are added and run on the main thread.
 	// The application option `OnShutdown` is run first.
@@ -617,12 +618,11 @@ func (a *App) OnShutdown(f func()) {
 	a.shutdownTasks = append(a.shutdownTasks, f)
 }
 
-func (a *App) Quit() {
+func (a *App) cleanup() {
 	if a.performingShutdown {
 		return
 	}
 	a.performingShutdown = true
-	// Run the shutdown tasks
 	for _, shutdownTask := range a.shutdownTasks {
 		InvokeSync(shutdownTask)
 	}
@@ -639,13 +639,15 @@ func (a *App) Quit() {
 		}
 		a.systemTrays = nil
 		a.systemTraysLock.Unlock()
-		if a.impl != nil {
-			a.impl.destroy()
-			a.impl = nil
-		}
 	})
 }
 
+func (a *App) Quit() {
+	if a.impl != nil {
+		InvokeSync(a.impl.destroy)
+	}
+}
+
 func (a *App) SetIcon(icon []byte) {
 	if a.impl != nil {
 		a.impl.setIcon(icon)
@@ -867,3 +869,10 @@ func (a *App) Environment() EnvironmentInfo {
 		Debug: a.isDebugMode,
 	}
 }
+
+func (a *App) shouldQuit() bool {
+	if a.options.ShouldQuit != nil {
+		return a.options.ShouldQuit()
+	}
+	return true
+}