准备工作（以下代码不用写）

typedef NS_ENUM(NSInteger, UIAlertControllerStyle) {
   UIAlertControllerStyleActionSheet = 0,// 从底部弹出
   UIAlertControllerStyleAlert// 从中心弹出
} NS_ENUM_AVAILABLE_IOS(8_0);

typedef NS_ENUM(NSInteger, UIAlertActionStyle) {
   UIAlertActionStyleDefault = 0,
   UIAlertActionStyleCancel,
   UIAlertActionStyleDestructive
} NS_ENUM_AVAILABLE_IOS(8_0);

上干货

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"文本对话框" message:@"登录和密码对话框" preferredStyle:UIAlertControllerStyleAlert];

UIAlertAction *OKAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
    // 停止监听文本改变通知
    [[NSNotificationCenter defaultCenter]removeObserver:self name:UITextFieldTextDidChangeNotification object:alertController.textFields.lastObject];
    // 打印第一个文本框的内容
    NSLog(@"%@",alertController.textFields.firstObject.text);
    
}];
[alertController addAction:OKAction];

UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:nil];
[alertController addAction:cancelAction];

 UIAlertAction *destructiveAction = [UIAlertAction actionWithTitle:@"警告" style:UIAlertActionStyleDestructive handler:nil];
[alertController addAction:destructiveAction];

[alertController addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {
    textField.backgroundColor = [UIColor redColor];
    textField.placeholder = @"请输用户名";   
}];

[alertController addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {
    textField.backgroundColor = [UIColor redColor];
    textField.placeholder = @"请输入密码";
    textField.secureTextEntry = YES;// 以圆点格式显示
    // 设置监听
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(handleTextDidChangeNotification:) name:UITextFieldTextDidChangeNotification object:textField];
    
}];

// 将OK按钮禁用
OKAction.enabled = NO;
self.alertAction = OKAction;//存储OK按钮

[self presentViewController:alertController animated:YES completion:nil];

从底部弹出提示框

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"OK/取消" message:@"请你登陆！" preferredStyle:UIAlertControllerStyleActionSheet];

UIAlertAction *OKaction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:nil];

UIAlertAction *cancleAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:nil];

UIAlertAction *destructiveAction = [UIAlertAction actionWithTitle:@"警告" style:UIAlertActionStyleDestructive handler:nil];

[alertController addAction:OKaction];
[alertController addAction:cancleAction];
[alertController addAction:destructiveAction];

[self presentViewController:alertController animated:YES completion:nil];