Updating constraints in textFieldDidBeginEditing method causes text to bounce - ios

Question

I have a UIView which contains another UIView object called contentView. Inside contentView, I have several UITextField objects. So that the current editing UITextField is always visible and not being hidden by the keyboard, I am altering the constraints on the contentView inside the textFieldDidBeginEditing: method. This means the contentView slides up and down inside the parent UIView, and keeps the relevant UITextField visible. This part is working fine, but here is a code fragment:
- (void)textFieldDidBeginEditing:(UITextField *)textField
//offset calculation removed for clarity
NSInteger offset = ....
self.contentViewTopConstraint.constant = -offset;
self.contentViewBottomConstraint.constant = offset;
[self.view setNeedsUpdateConstraints];
[UIView animateWithDuration:0.3 animations:^{
[self.view layoutIfNeeded];
}];
}
I have noticed that if I type some text into the first UITextField, and then tap on the second UITextField, the text in the first UITextField jumps upwards and then back down again. If I disable the animation in the above code fragment, this behaviour goes away. So my guess is that when editing a UITextField, some other constraints are set, which are then altered as focus moves away from that UITextField. As I'm telling the view to update it's constraints in an animated fashion, this causes the text to move around.
Is there some way I can avoid this, but still maintain the animation for moving the contentView up and down?
Edit: Adding an extra [self.view layoutIfNeeded] call before I update any constraints fixed the issue. I'm still not to sure what might have been going on though, or really why this fixed it. Anyone have any insight?

Answer 1

I have since learned that the correct way to animate constraints is like this:
- (void)textFieldDidBeginEditing:(UITextField *)textField
//offset calculation removed for clarity
NSInteger offset = ....
[self.view layoutIfNeeded];
self.contentViewTopConstraint.constant = -offset;
self.contentViewBottomConstraint.constant = offset;
[UIView animateWithDuration:0.3 animations:^{
[self.view layoutIfNeeded];
}];
}
This resolved the issue I was having.

Answer 2

I am not sure what is wrong with your piece of code, more code would be required for me to tell what is wrong in that, But you can use this piece of code, it will work for you
-(void)addObservers
{
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(keyboardIsShowing:)
name:UIKeyboardWillShowNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(keyboardIsHiding:)
name:UIKeyboardWillHideNotification
object:nil];
}
-(void)removeObservers
{
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];
}
- (void)keyboardIsShowing:(NSNotification*)notification
{
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:[notification.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue]];
[UIView setAnimationCurve:[notification.userInfo[UIKeyboardAnimationCurveUserInfoKey] integerValue]];
[UIView setAnimationBeginsFromCurrentState:YES];
int scaleFactor = 0;
if([oldPasswrdField isFirstResponder])
scaleFactor = 20;
else if([newPasswrdField isFirstResponder])
scaleFactor = 76;
else if([confirmPasswrdField isFirstResponder])
scaleFactor = 132;
self.contentView.frame = CGRectMake(self.contentView.frame.origin.x, self.view.frame.origin.y-scaleFactor,self.contentView.frame.size.width, self.contentView.frame.size.height);
[UIView commitAnimations];
}
- (void)keyboardIsHiding:(NSNotification*)notification
{
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:[notification.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue]];
[UIView setAnimationCurve:[notification.userInfo[UIKeyboardAnimationCurveUserInfoKey] integerValue]];
[UIView setAnimationBeginsFromCurrentState:YES];
self.contentView.frame = CGRectMake(self.contentView.frame.origin.x, 0, self.contentView.frame.size.width, self.contentView.frame.size.height);
//self.view.frame = frame;
[UIView commitAnimations];
}
You see the scalefactor in keyboardIsShowing method. It is needed to be set according to the textfield you are editing. If you can, you can just fetch the current responding text field and take it's origin.y and set the scale factor according to that. Also, call addObservers in viewDidAppear and call removeObservers in viewDidDisappear. Or according to your needs, but don't forget to call them both once.
Edit: Tell me if this works for you or if you need further help on the matter, would be glad to assist.