UIAlertController的使用

    UIAlertController *alert =[UIAlertController alertControllerWithTitle:@"提醒" message:@"请选择" preferredStyle:UIAlertControllerStyleAlert];    UIAlertAction *action =[UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:nil];    [alert addAction:action];    [self presentViewController:alert animated:YES completion:nil];