Determine whether a class exists

We will inevitably use classes not available in earlier versions during development. If we want to make our applications compatible with multiple versions as much as possible, we need to consider what to do if the class we use is not in a lower version. Class pkClass = NSClassFromString (@ "PKAddPassesViewController"); if (pkClass) {NSLog (@ "available"); // if applicable, we can use some features of passkit} else {www.2cto.com NSLog (@ "unavailable"); if not, we should prompt the user, or perform some other processing} NSString * pkClassStr = NSStringFromClass ([PKAddPassesViewController class]); if (pkClassStr) {NSLog (@ "available"); // if applicable, we can use some passkit functions} else {NSLog (@ "unavailable"); if not, we need to prompt the user or perform some other processing}