When we click on TextField  keyboard lifts up but if our text field is at bottom then we are not able to see it so with the help of NSNotificationCenter we can solve this issue.

Add one TextField in ViewController, give bottom constraint to it and make the outlet of textfield and bottom constraint. In viewDidLoad write below line of code.

- (void)viewDidLoad {
    [super viewDidLoad];
    
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillShow:)
                                                 name:UIKeyboardWillShowNotification
                                               object:self.view.window]; //addObserver is used to receive the notifications.
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillHide:)
                                                 name:UIKeyboardWillHideNotification
                                               object:[[self view] window]];

   
}

As in NSNotificationCenter we declare a method name keybaordWillShow so now we have to define it by using below code.

- (void)keyboardWillShow:(NSNotification *)notification{
    
      NSDictionary* userInfo = [notification userInfo]; 
    NSLog(@"user Info is %@",userInfo);
    
    CGSize keyboardSize = [[userInfo objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size; //here we will got the keyboard size and with the help of this we can uplift the textfiled with the keyboard
    NSLog(@"keyboard size %f",keyboardSize.height);
    
    [UIView animateWithDuration:0.5 animations:^{
        _bottomConstraints.constant = keyboardSize.height;// _bottom constraint is the bottom constraint of the textfiled.
        [self.view layoutIfNeeded];
    }];
    
}

Now in keyboardWillHide method write below code

- (void)keyboardWillHide:(NSNotification *)notification{
    
     [UIView animateWithDuration:0.5 animations:^{
        _bottomConstraints.constant = 97;
        [self.view layoutIfNeeded];
    }];
}