iOS9提示框的正确使用方式

但是在实际的工程开发中，我们有这样一个“潜规则”：要把每一个警告（warning）当做错误（error）。所以为了顺应苹果的潮流，我们来解决这个warning，使用UIAlertController来解决这个问题。代码如下：

#import "LoginViewController.h"

@interface LoginViewController ()
@property (weak, nonatomic) IBOutlet UITextField *passWord;

@property (weak, nonatomic) IBOutlet UITextField *userName;


@property (weak, nonatomic) IBOutlet UIButton *login;
- (IBAction)loginOnClick:(UIButton *)sender;

@end

@implementation LoginViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  //获取通知中心
  NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
  //注册通知
  [center addObserver:self selector:@selector(textChange) name:UITextFieldTextDidChangeNotification object:self.userName];
  [center addObserver:self selector:@selector(textChange) name:UITextFieldTextDidChangeNotification object:self.passWord];

}

-(void)textChange
{
  //当用户名框和密码框同时有内容时，登录按钮才可以点击
  self.login.enabled = (self.userName.text.length > 0 && self.passWord.text.length > 0);

}


//点击登录按钮执行的事件
- (IBAction)loginOnClick:(UIButton *)sender {

  if ([self.userName.text isEqual: @"xiaojin"] && [self.passWord.text isEqual: @"123456"]) {
    NSLog(@"successful");
    [self performSegueWithIdentifier:@"loginIdentifier" sender:nil];
  } else {

    //初始化提示框；
    UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"提示" message:@"用户名或密码出现错误" preferredStyle: UIAlertControllerStyleAlert];

    [alert addAction:[UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
      //点击按钮的响应事件；
    }]];

    //弹出提示框；
    [self presentViewController:alert animated:true completion:nil];
  }
}

@end