创建IOS的alert界面

////  MyViewController.m//  Demo6_Alert警告框////  //#import "MyViewController.h"@interface MyViewController ()@end@implementation MyViewController- (IBAction)buttonClick:(id)sender {    //需要弹出警告框    //1.创建UIAlertController实例    UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"title" message:@"message" preferredStyle:UIAlertControllerStyleAlert];    //2.创建意图按键    UIAlertAction *actionYES = [UIAlertAction actionWithTitle:@"YES" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {        //把AlertController中所有的 textField取出        NSArray *fields = alert.textFields;        //把 第一个添加的 textField取出        UITextField *userNameField = fields[0];        //把 第二个添加的 textField取出        UITextField *pwdField = fields[1];        //判断用户名是否是 abc  密码 是否是 123        if ([userNameField.text isEqualToString:@"abc"] && [pwdField.text isEqualToString:@"123"]) {            //点钟action后做什么事情            NSLog(@"登录成功");            //重新弹出一个对话框， title 提示  message 登录成功  action 确定        }else {            NSLog(@"登录失败");                    }    }];                UIAlertAction *actionNO = [UIAlertAction actionWithTitle:@"NO" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {        NSLog(@"actionNO 被点中");    }];    //3.将 alertAction 添加到 AlertController中    [alert addAction:actionYES];    [alert addAction:actionNO];        //4.向AlertController中添加textField    [alert addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {        //在bolck中可以设置 今天添加的textField进行设置        //设置 占位符        textField.placeholder = @"请重新输入用户名";    }];    [alert addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {        textField.textColor = [UIColor redColor];         textField.placeholder = @"请重新输入密码";        textField.secureTextEntry = YES;//密码样式    }];                        //5.显示AlertController    [self presentViewController:alert animated:YES completion:nil];    }- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view from its nib.}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}/*#pragma mark - Navigation// In a storyboard-based application, you will often want to do a little preparation before navigation- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {    // Get the new view controller using [segue destinationViewController].    // Pass the selected object to the new view controller.}*/@end